*Article* **Higher Ventricular-Arterial Coupling Derived from Three-Dimensional Echocardiography Is Associated with a Worse Clinical Outcome in Systemic Sclerosis**

**Francesco Tona 1,\*,†, Elisabetta Zanatta 2,†, Roberta Montisci 3, Denisa Muraru 1, Elena Beccegato 1, Elena De Zorzi 2, Francesco Benvenuti 2, Giovanni Civieri 1, Franco Cozzi 2, Sabino Iliceto <sup>1</sup> and Andrea Doria <sup>2</sup>**


**Abstract:** Primary myocardial involvement is common in systemic sclerosis (SSc). Ventricular-arterial coupling (VAC) reflecting the interplay between ventricular performance and arterial load, is a key determinant of cardiovascular (CV) performance. We aimed to investigate VAC, VAC-derived indices, and the potential association between altered VAC and survival free from death/hospitalization for major adverse CV events (MACE) in scleroderma. Only SSc patients without any anamnestic and echocardiographic evidence of primary myocardial involvement who underwent threedimensional echocardiography (3DE) were included in this cross-sectional study and compared with healthy matched controls. 3DE was used for noninvasive measurements of end-systolic elastance (Ees), arterial elastance (Ea), VAC (Ea/Ees) and end-diastolic elastance (Eed); the occurrence of death/hospitalization for MACE was recorded during follow-up. Sixty-five SSc patients (54 female; aged 56 ± 14 years) were included. Ees (*p* = 0.04), Ea (*p* = 0.04) and Eed (*p* = 0.01) were higher in patients vs. controls. Thus, VAC was similar in both groups. Ees was lower and VAC was higher in patients with diffuse cutaneous form (dcSSc) vs. patients with limited form (lcSSc) (*p* = 0.001 and *p* = 0.02, respectively). Over a median follow-up of 4 years, four patients died for heart failure and 34 were hospitalized for CV events. In patients with VAC > 0.63 the risk of MACE was higher (HR 2.5; 95% CI 1.13–5.7; *p* = 0.01) and survival free from death/hospitalization was lower (*p* = 0.005) than in those with VAC < 0.63. Our study suggests that VAC may be impaired in SSc patients without signs and symptoms of primary myocardial involvement. Moreover, VAC appears to have a prognostic role in SSc.

**Keywords:** heart failure; 3D-echocardiography; ventricular function; outcome; systemic sclerosis; ventricular-arterial coupling

#### **1. Introduction**

Systemic sclerosis (SSc) is a chronic systemic autoimmune disease characterized by widespread vascular lesions and fibrosis of skin and internal organs [1]. Although often clinically silent [2,3], primary cardiac involvement is one of the main causes of death in SSc [4,5]. Thus, a yearly transthoracic echocardiography is recommended in patients with SSc to assess systolic pulmonary artery pressure as well as diastolic and systolic function of the left ventricle (LV) [6]. In this regard, some measurements such as end-diastolic diameter, fractional shortening, or LV ejection fraction (LVEF) are routinely used in clinical

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**Citation:** Tona, F.; Zanatta, E.; Montisci, R.; Muraru, D.; Beccegato, E.; De Zorzi, E.; Benvenuti, F.; Civieri, G.; Cozzi, F.; Iliceto, S.; et al. Higher Ventricular-Arterial Coupling Derived from Three-Dimensional Echocardiography Is Associated with a Worse Clinical Outcome in Systemic Sclerosis. *Pharmaceuticals* **2021**, *14*, 646. https://doi.org/10.3390/ph14070646

Academic Editors: Francesco Salton, Barbara Ruaro and Paola Confalonieri

Received: 2 March 2021 Accepted: 2 July 2021 Published: 5 July 2021

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**Copyright:** © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

practice. However, these indices are load-dependent and do not systematically reflect the contractile state of the myocardium [7]. The interplay between cardiac function and arterial system—commonly defined as ventricular-arterial coupling (VAC)—is a major determinant of ventricular performance as it reflects global cardiovascular (CV) efficiency [8], and can be mathematically expressed as the ratio between arterial elastance (Ea) and end-systolic elastance (Ees) of the LV. VAC has been recently recognized as a key determinant of cardiovascular performance, and in fact, ventricular-arterial uncoupling which occurs in various clinical conditions, may predict morbidity and mortality [9–11].

The advantages of three-dimensional echocardiography (3DE) vs. 2-dimensional echocardiography (2DE) lie in its better accuracy, precision, and reproducibility for volume measurements [12], and consequently for VAC assessment [13].

We aimed to investigate VAC by 3DE in SSc patients, as well as potential differences in VAC values and VAC-derived indices by comparing patients with a limited and diffuse cutaneous form of SSc (lcSSc and dcSSc, respectively). Moreover, we set out to evaluate a potential association between altered VAC and survival-free from major adverse cardiovascular events (MACEs) in SSc.

#### **2. Results**

#### *2.1. Echocardiography and Pressure-Volume Curve Parameters in SSc Patients and Controls*

Baseline characteristics of the 65 patients enrolled in the study are shown in Table 1. LV diastolic dimension, wall thickness, and mass index were comparable in patients and in controls. Regional contractility was normal in all patients and controls. Left ventricular end-systolic volume (LVESV), LV end-diastolic volume (LVEDV), stroke volume (SV), and LVEF were similar in both groups. Systolic and diastolic blood pressure were comparable in patients and controls. E/e' was higher in patients vs. controls (10.02 ± 4.3 vs. 6.5 ± 2.2, *p* < 0.0001). Ees and Ea were higher in patients vs. controls (3.95 ± 1.8 vs. 2.99 ± 0.7 mmHg/mL, *p* = 0.002; 2.28 ± 0.11 vs. 1.73 ± 0.07 mmHg/mL, *p* = 0.001, respectively), whereas VAC was comparable in both groups (0.60 ± 0.1 vs. 0.62 ± 0.2, *p* = 0.59). Diastolic elastance (Eed) was higher in patients (0.23 ± 0.01 vs. 0.16 ± 0.03 mmHg/mL, *p* = 0.001). Stroke work (SW), potential energy (PE), pressure-voulme area (PVA) and LV efficiency indicating mechanical energy exerted by the left ventricle were similar in both groups.

**Table 1.** Clinical and Echocardiographic Features in SSc Patients with and without VAC > 0.63.


#### **Table 1.** *Cont.*


BMI, body mass index; DT, E-wave deceleration time; ET-1, endothelin 1; E/A, ratio of early transmitral diastolic flow velocity (E) and flow velocity during atrial contraction (A); HRCT, high resolution computed tomography; ILD, interstitial lung disease; IVS, interventricular septum; LV, left ventricle; LVEDD, left ventricular enddiastolic diameter; LVEDV, left ventricular end-diastolic volume; LVEF, left ventricular ejection fraction; LVESV, left ventricular end-systolic volume; PAH, pulmonary arterial hypertension; PAP, pulmonary arterial pressure; PW, posterior wall; RP, Raynaud phenomenon; RVEDD, right ventricular end-diastolic dimension; SSc, systemic sclerosis; SV, stroke volume; TAPSE, tricuspid annular plane excursion. Values are mean ± SD or median (IQR).

#### *2.2. Echocardiography and Pressure-Volume Curve Parameters According to VAC Value*

Patients in the higher VAC group (>0.63) had significantly higher LVESV (*p* < 0.0001) with reduced LVEF (*p* < 0.0001) than those with lower VAC (≤0.63). Ees was lower in patients with VAC > 0.63 (*p* < 0.0001) whereas Ea was similar in both groups (Table 1). Disease duration was longer (*p* = 0.03) and the prevalence of diffuse cutaneous SSc (dcSSc) was higher (*p* = 0.03) in patients with VAC > 0.63. Ongoing medications were comparable between the two groups.

#### *2.3. Echocardiography and Pressure-Volume Curve Parameters in dcSSc and lcSSc Patients*

Table 2 shows the differences between patients with dcSSc vs. lcSSc. In particular, LVEDV (*p* = 0.004), LVESV (*p* = 0.001), and SV (*p* = 0.03) were higher in dcSSc patients and LVEF was lower, albeit within the normal range (*p* = 0.01). Ea (*p* = 0.01) and Ees (*p* = 0.001) were lower in dcSSc patients. VAC was significantly higher in dcSSc patients (*p* = 0.02). PE was higher in dcSSc (*p* = 0.01) and LV efficiency was lower (*p* = 0.02) (Table 2). Ees correlated with Ea (ρ = 0.851, *p* < 0.0001). However, in dcSSc the correlation line is shifted upward and to the left. For the same Ea value, patients with dcSSc presented a lower Ees, indicative of inadequate contractility (Figure 1).

**Table 2.** Clinical and Echocardiographic Features in dcSSc Patients versus lcSSc Patients.



#### **Table 2.** *Cont.*

Abbreviations as in Table 1. Values are mean ± SD or median (IQR).

**Figure 1.** Scatterplot of the relationship between Ea and Ees in patients with lcSSc and patients with dcSSc. Ees correlates with Ea both in lcSSc (ρ = 0.779, *p* < 0.0001) and, albeit more weakly, in dcSSc (ρ = 0.599, *p* = 0.002).

#### *2.4. Correlations of Pressure-Volume Curve Parameters*

Unlike Ees and VAC (ρ = −0.456, *p* < 0.0001 and ρ = 0.336, *p* = 0.008, respectively), Ea did not correlate with time elapsed from SSc diagnosis (ρ = 0.035, *p* = 0.78). Ea positively correlated with Eed (ρ = 0.857, *p* < 0.0001) and systolic pulmonary arterial pressure (ρ = 0.401, *p* = 0.002), and inversely with TAPSE (ρ = −0.434, *p* = 0.007). Ees positively correlated with Eed (ρ = 0.811, *p* < 0.0001). Eed inversely correlated with TAPSE (ρ = −0.447, *p* = 0.001).

#### *2.5. Association between VAC and Other Clinical Variables*

At univariate linear regression analysis, diagnosis of dcSSc (*p* = 0.009), therapy with prostanoid (*p* = 0.03), disease duration (*p* = 0.01) and age at diagnosis (*p* = 0.02) were determinants of VAC. To further investigate the potential factors involved in VAC alterations, we performed a multivariable linear regression (stepwise) including significant factors at univariate linear regression analysis which revealed that only diagnosis of dcSSc had an independent influence on VAC (Table 3).

**Table 3.** Independent Effects of Clinical Variables on VAC.


Note: Using multivariable linear regression analysis with stepwise method.

#### *2.6. Factors Associated with VAC > 0.63*

In univariable logistic regression VAC > 0.63 was associated with time elapsed from diagnosis (*p* = 0.01), age at SSc onset (*p* = 0.04), diagnosis of dcSSc (*p* = 0.03), and LVESV (*p* = 0.002). In multivariable logistic regression, adjusted for age and sex, VAC > 0.63 was associated with LVESV (OR 1.076; 95% CI 1.012–1.144; *p* = 0.02) and time elapsed from diagnosis (OR 1.057; 95% CI 1.008–1.127; *p* = 0.04).

#### *2.7. Major Adverse Cardiac Events*

During a 4-year median follow-up (IQR, 2–10 years), 38 patients (58.5%) developed major adverse cardiac events (MACEs). Four patients (6%) died from heart failure, 16 (24%) were hospitalized for heart failure and 18 (28%) for angina (n = 12, 67%; nine without coronary epicardial stenosis and three with epicardial coronary stenosis), or myocardial infarction (n = 6, 33%). Twelve out of 16 (75%) of the heart failure episodes were with low ejection fraction (HFrEF). No heart failure episode was of right-sided origin. There were non-cardiovascular death or events during the follow-up period.

Differences between patients with and without MACEs are shown in Table 4. Time from SSc diagnosis was longer and LVEF was lower in patients with MACEs (*p* = 0.03 and *p* = 0.01, respectively). LVESV tended to be greater in patients with MACEs (*p* = 0.06). Ea was similar in patients with and without MACEs (*p* = 0.52). Ees was lower (*p* = 0.01) and VAC was higher (*p* = 0.008) in patients with MACEs. LV efficiency was lower in patients with MACEs (*p* = 0.01). VAC was >0.63 in 23/38 (60%) patients with MACEs and in 8/27 (29%) patients without MACEs (*p* = 0.01). Figure 2 shows the cumulative survival free from MACEs according to VAC value.


**Table 4.** Clinical and Echocardiographic Features in Patients with and without MACEs.



Abbreviations as in Table 1. Values are mean ± SD or median (IQR).

**Figure 2.** Kaplan Meier estimate of survival free from hospitalizations of patients with VAC ≤ 0.63 (in black), and patients with VAC > 0.63 (in yellow).

#### *2.8. Risk Factors for MACEs in the Study Cohort*

In univariable Cox regression analysis, MACEs were associated with VAC > 0.63 (*p* = 0.008), LVEF < 62% (*p* = 0.02), LV efficiency < 76% (*p* = 0.02) and disease duration (*p* = 0.01). In the final multivariable regression model, also adjusted for age, sex, pulmonary hypertension, dcSSc and interstitial lung disease, VAC > 0.63 was independently associated with MACEs (HR 2.5; 95% CI 1.13–5.7; *p* = 0.01) (Table 5). The C statistic for multivariable model increased from 0.82 to 0.92 when adding VAC > 0.63 (*p* = 0.001) (Figure 3).

**Table 5.** Univariate and Multivariable Predictors of MACEs.



**Table 5.** *Cont.*

CI. confidence interval; HR, hazard ratio; HRCT, high resolution computed tomography; ILD, interstitial lung disease; LVEDV, left ventricular end-diastolic volume; LVEF, left ventricular ejection fraction; LVESV, left ventricular end-systolic volume; MACE, major adverse cardiac events; PAH, pulmonary arterial hypertension; PAP, pulmonary arterial pressure; SV, stroke volume; TAPSE, tricuspid annular plane excursion.


**Figure 3.** Receiving operating curves in model 1 and model 2 (including VAC > 0.63) for MACEs. C-statistic improves adding VAC > 0.63 in the multivariable model \* *p* value is derived from comparison of model 1 to model 1 plus VAC > 0.63 (model 2).

#### *2.9. Incremental Value of VAC for Predicting Adverse Cardiac Events*

To assess the incremental prognostic value of VAC, global chi-square scores were calculated (Figure 4). The addition of VAC > 0.63 (global chi-square: 13.1) significantly increased the global chi-square score (19.2; *p* = 0.02).

**Figure 4.** Incremental prognostic value of VAC > 0.63 when added to LVEF, LV efficiency, disease duration, age, sex, pulmonary hypertension, dcSSc and interstitial lung disease (Model 1).

#### *2.10. Intra and Interobserver Reproducibility of VAC by 3D*

Intraobserver reproducibility was high (r = 0.98, SEE = 0.12); the mean difference was −0.02 and the upper and lower limits of agreement between the measurements were +0.14 (95% CI, +0.08 to +0.2) and −0.19 (95% CI, −0.26 to −0.13), respectively; intraclass correlation coefficient was 0.986. Interobserver reproducibility was also high (r = 0.96, SEE =0.18); the mean difference was 0.01 and the upper and lower limits of agreement between the 2 measurements were +0.36 (95% CI, +0.26 to +0.45) and −0.33 (95% CI, −0.43 to −0.23), respectively; intraclass correlation coefficient was 0.966.

#### *2.11. Ventricular-Arterial Coupling by 2D and 3D Echo Modalities*

Table 6 presents the comparison between 2D and 3D parameters. Although Ea and VAC were similar between 2D and 3D echocardiography, Ees was lower by 3D echocardiography.

**Table 6.** Arterial elastance, End-systolic elastance and Ventricular-arterial coupling by 2D and 3D echocardiography (*n* = 65).


Figure 5 presents a linear regression plot (left panel) and Bland–Altman analysis (right panel) for VAC computed by 2D- and 3D-echocardiography.

**Figure 5.** Linear regression (**left**) and Bland-Altman analysis (**right**) for VAC between 2D and 3D-echocardiography. Scattergram (**left** panel) showing the correrelation plot between VAC obtained by 2D- and 3D echocardiography. Plot of the difference (**right** panel) between the VAC measurements against their mean is shown. Medial line represents bias while the upper and lower red dotted lines the levels of agreement Dotted lines represent boundaries of means ± 2 SD, from −1.96 to +1.96. Relative mean error was calculated by the ratio of absolute difference of two values over their average.

#### **3. Discussion**

Standard transthoracic measurements derived from echocardiography such as enddiastolic diameter, fractional shortening, or LVEF are routinely used in clinical practice. However, these indices are load-dependent and do not systematically reflect the contractile state of the myocardium.

Our main findings indicate that: (1) VAC by 3DE may be significantly higher in dcSSc patients than in lcSSc patients, despite normal LVEF and worsen in relation to disease duration; (2) VAC by 3DE may predict major cardiovascular events in SSc.

As LV and arterial system are anatomically continuous, their interaction is a crucial determinant of cardiovascular function [14,15]. Notably, and to the best of our knowledge, this is the first study to assess LV pressure-volume relationship and VAC by 3DE in SSc. 3DE allows for a more precise evaluation of LV volumes than 2D echocardiography [12] and this is paramount for a correct assessment of VAC. Comparison with two-dimensional measurements was beyond the scope of our study. Nevertheless, in our 65 patients we found a Pearson correlation r = 0.87 between 2D and 3D echocardiography (*p* = 0.0001) (data not shown).

In our study, the traditional indices of the LV (i.e., LVEDV, LVESV and LVEF) in SSc patients were similar to that observed in controls and SV tended to be lower (*p* = 0.07) in the former. However, Ea was higher and Ees was significantly higher in SSc patients. Thus, VAC was similar in SSc patients and controls. Eed was higher in patients, indicating high filling pressure. This hemodynamic arrangement is peculiar to heart failure with preserved ejection fraction (HF*p*EF) [11,14], one of the typical and prognostically negative clinical manifestations of cardiac involvement in SSc. We corroborated previous reports indicating high frequencies of impaired diastolic function in SSc. A recent study conducted on a large and unselected SSc cohort showed more frequent and severe diastolic dysfunction (2016 guidelines definition) during the disease course and a high impact on mortality in SSc [16].

Many studies have reported a low prevalence of systolic dysfunction in SSc patients [3,17,18]. However, we hypothesize that conventional echocardiography may cause LV systolic dysfunction to be underestimated. Although we found no differences in the diastolic function between dcSSc and lcSSc, as previously reported [16], there appears to be significant hemodynamic differences between the two main subgroup of SSc patients with different cutaneous form. In fact, our findings point to a predominant intrinsic LV systolic dysfunction in dcSSc and LV inability to compensate higher afterload, rather than important differences in load. The higher afterload in SSc may be attributable to increased arterial stiffness from deposition of collagen and other matrix components [19]. This is supported by the higher Ea value found in our study and correlates with a worse prognosis. In fact, in the recent consensus on the role of VAC [11] the Authors highlighted that extracellular matrix and cytoskeleton regulation processes are biochemical pathways that concomitantly affect cardiac and arterial structure and function through replacement or reactive fibrosis, which typically occurs in in SSc patients. The same Authors note that the measurement of VAC may be useful for not only SSc patients but also for patients with other cardiovascular diseases [11].

The inability of the contractile function of the myocardium to adapt to the afterload is evident from our results, mostly in patients with dcSSc. Impaired contractility and ventricular-arterial uncoupling may stem from coronary microvascular dysfunction and remodeling [20]. Moreover, VAC may be associated with future risk of coronary events due to microvascular dysfunction rather than coronary epicardial atherosclerotic stenosis. Endothelial-derived nitric oxide, oxidative stress and cytokines are main regulators of myocardial microcirculation, as well as aortic vasoreactivity. Furthermore, the decreased autonomic nervous system activity in SSc individuals may result in significant impairment of LV structure, function and mechanics [21]. Finally, as above mentioned, myocardial fibrosis could also play a prominent role [1]. In this regards, the imbalance between extracellular matrix synthesis and degradation by metalloproteinases has been highlighted as a prominent mechanism underlying impaired VAC.

Pulmonary arterial hypertension (PAH) typically affects the right ventricle, whereas the presence of LV abnormalities due to PAH is very uncommon (less than 1% of patients). In this regards, some studies have demonstrated the occurrence of right ventricular-arterial uncoupling in PAH but, to the best of our knowledge, no study have investigated or demonstrated the presence of high left VAC in PAH, due to the absence of a pathophysiological rationale. Moreover, the values of PAPs in our SSc patients with PAH are quite low (mean 34 mmHg), so the possibility of an impact on the left heart is highly unlikely. In line with this rationale, our study patients with VAC > 0.63 did not shown higher rate of PAH or higher level of pulmonary pressure values. Moreover, PAH was not a determinant of VAC in our linear regression analysis. Considering all this aspects, we did not consider useful to exclude these patients, which would considerably reduce the sample size of the study and its relevance.

VAC has been recently recognized as a key determinant of cardiovascular performance and its prognostic role has been demonstrated in various conditions [11]. For the first time, we provided data on the prognostic role of VAC in SSc, thus contributing to clarify the prognostic significance of subclinical cardiac alterations detected by imaging, one of the main unresolved issues in SSc. Our findings support a possible role for VAC in stratifying SSc patients with a major cardiovascular risk. Further prospective studies on larger cohorts are warranted to corroborate our findings.

While specific therapies for SSc cardiomyopathy are still lacking, vasoactive drugs have proven effective in mitigating myocardial perfusion and function abnormalities using conventional techniques. In addition, even low-dose acetylsalicylic acid has been recently associated with a lower incidence of distinct primary myocardial disease manifestations in SSc [22,23]. In this scenario, VAC evaluation may help identify patients who would most benefit from an early and more aggressive treatment with vasodilators and acetylsalicylic acid, to prevent myocardial dysfunction and reduce future MACEs. In this regards it is worth mentioning that—according to emerging evidences—even subclinical inflammation seems play a role in SSc cardiomyopathy. Given that systemic inflammation has been recognized as another potential pathogenetic mechanisms underlying VAC, its assessment might be useful in the longitudinal evaluation of SSc patients ad it pertains the potential benefit of immunosuppressants on subclinical myocardial dysfunction in SSc, as it has been suggested for rheumatoid arthritis.

As a limitation of the study, we should mention the relatively small sample size and monocentric nature of our study. Although statistically significant differences were observed, we acknowledge that our study may be slightly underpowered. A post-hoc power analysis (assuming α = 0.05) estimated that with 34 patients with VAC ≤ 0.63 and

31 patients with VAC > 0.63, with an event incidence of 44% in patients with VAC ≤ 0.63 and 74% in patients with VAC > 0.63, we reject the null hypothesis of equal survival with 75% power. In addition, we were not able to demonstrate the exact mechanisms underlying the subtle changes in myocardial contractility, based on other methods, such as cardiac magnetic resonance imaging. Myocardial fibrosis, which is a potential mechanism of myocardial dysfunction in SSc, was not investigated. Although we did not perform coronary angiography to exclude coronary heart disease, all patients were asymptomatic and the pre-test probability was low based on atherosclerotic risk factors, and there were no significant differences vs. controls. Moreover, we did not measure the global longitudinal strain (GLS) and therefore we do not have data of correlation between GLS and LV elastance. Therefore, because LGS is an early and well proved indicator of LV systolic dysfunction, it would be useful for identification of LV dysfunction in SSc patients.

#### **4. Materials and Methods**

#### *4.1. Study Population*

We conducted a retrospective cohort study that comprised patients attending the Rheumatology Unit of Padova University Hospital. The study population was retrieved from the database of our Echocardiography Laboratory. Overall, three hundred fifty patients underwent echocardiogram between January 2014 and March 2016 [24].

• Inclusion and Exclusion Criteria

Among the 350 patients, only those patients who were evaluated by 3DE were included (Figure 6). All patients were affected with SSc according to ACR/EULAR classification criteria [24].

Exclusion criteria were as follows: patients undergoing only 2DE (*n* = 250); patients (*n* = 35) with evidence of structural heart diseases (cardiomyopathy of any origin, significant valvular heart disease, coronary artery disease or myocardial infarction), atrial fibrillation, diabetes mellitus or systemic arterial hypertension grade II/III according to the European Society of Hypertension/European Society of Cardiology 2018 guidelines [25]; glomerular filtration rate <30 mL min−<sup>1</sup> per 1.73 m2, cancer in the past 5 years, end-stage ILD and dyslipidemia.

**Figure 6.** Study flow diagram. SSc, Sytemic Sclerosis.

Ultimately, we enrolled 65 SSc patients (54 female; age 56 ± 14 years) with no signs and symptoms of primary myocardial involvement (Figure 6), according to the available echocardiogram, and to clinical history, physical examination and ECG reported in clinical records within the previous six months.

Baseline evaluation included physical examination, gathering demographic and clinical data, and echocardiographic features (Table 1). Several disease features (e.g., cutaneous form, digital ulcers) and other organ involvement (e.g., interstitial lung disease, ILD) were recorded.

A series of 30 age- and sex-matched subjects satisfying the same exclusion criteria were evaluated by 3DE as controls. Given the retrospective nature of the study the written informed consent had been obtained by all patients at time of 3DE examination: this was a generic consensus to the acquisition of 3D images, beyond 2D standard Echocardiography.

#### *4.2. Echocardiography*

Echocardiography was performed using Vivid 7 ultrasound systems (GE Healthcare, Horten, Norway) with a 2.5-MHz transducer by 2 experienced cardiologists (F.T. and D.M.). All participants were examined with conventional 2-dimensional echocardiography and color tissue Doppler (TDI). All echocardiograms were stored on magneto-optical disks and an external FireWire hard drive (LaCie, France) and analyzed off line with commercially available software (EchoPac version 2008; GE Medical, Horten, Norway). Measurements of LV internal dimensions and LV mass index (LVMI) were performed and calculated according to European and American recommendations [26]. LV mass/body surface area ≤116 g/m<sup>2</sup> in men and ≤104 g/m<sup>2</sup> in women was considered normal. None of the patients suffered from significant valvular disease. In each subject, LVEF was measured and diastolic dysfunction was defined according to the American Society of Echocardiography criteria [27]. We considered abnormal an E/e > 14, and sign of diastolic dysfunction.

Echocardiographic parameters of diastolic function including the ratio between early (E) and late (A) peak velocities of the mitral inflow, E/A, and pulsed-wave tissue Doppler velocities of the mitral annulus in early diastole in the lateral wall (e ) were used as surrogates of LV diastolic relaxation and compliance and the deceleration time (DT) as a surrogate of early LV stiffness, and E/e as surrogate estimate of LV filling pressure [28]. All measures were averaged over 3 heart cycles.

#### 4.2.1. Transthoracic Real-Time 3D Imaging

Three-dimensional echocardiography data set acquisition of the LV was performed by the same examiner at the end of the standard 2DE examination using a 3Volume matrixarray transducer (GE Healthcare). A full-volume scan was acquired using second-harmonic imaging from apical approach, and care was taken to encompass the entire LV cavity in the data set. Consecutive four- to six-beat ECG-gated subvolumes were acquired during an end-expiratory apnoea to generate the full-volume data set. The quality of the acquisition was then verified in each patient by selecting twelve-slice display mode available on the machine to ensure that the entire LV cavity is included in the 3DE full volume, and, if unsatisfactory, the data set was re-acquired. Data sets were stored digitally in raw-data format and exported to a separate workstation equipped with commercially available software for offline analysis of LV volumes and LVEF from 3DE data sets: 4D AutoLVQ™ (EchoPac 202, GE Vingmed, Horten, Norway).

#### 4.2.2. Left Ventricular Volume Measurements

Left ventricular analysis was performed in several steps [29,30]:

(1) Automatic slicing of LV full-volume data set. The end-diastolic frames needed for contour detection were automatically displayed in quad-view: apical four-, twochamber, long-axis views and LV short-axis plane. Each longitudinal view was color-coded and indicated on the short-axis image at 60◦ between each plane. Both

reference frames in the end-systole and end-diastole could be also manually selected, if necessary.


The intra- and inter-observer reproducibility for systolic function parameters in 20 randomly selected patients were good. Concordance between two raters using the Kappa statistic was 0.95 (*p* < 0.0001).

#### 4.2.3. Variables Derived from Left Ventricular Pressure-Volume Relations

To noninvasively quantify ventricular contractility, we calculated Ees as end-systolic pressure (ESP) divided by LVESV. LVEDV is an index of LV size and quantifies the degree of cardiac remodeling. The end-systolic pressure volume relationship (ESPVR) provides a load-independent measure of contractile function. The ESPVR is typically assumed to be linear and is therefore defined by a slope and an intercept. Although many studies focus on the slope alone, both the slope (end-systolic elastance [Ees]) and the intercept (V0) are required to describe the contractile state of the left ventricle. Ees quantifies ventricular elastance (stiffness) at end-systole, and V0 is a measure of ventricular volume at a theoretical end systolic pressure of 0 mm Hg. Because V0 is an extrapolated value obtained at a nonphysiological pressure, the LVESV at a systolic pressure of 100 mm Hg (V100) is also often described. For arterial load, Ea was the ratio of ESP to stroke volume (SV), and VAC was defined as the ratio of Ea to Ees. For these equations, LVESV and SV were obtained from 3DE results. ESP was defined as 0.9 x systolic blood pressure determined by noninvasive blood pressure measurement at the same time as 3DE. As recommended by the ESC guidelines on hypertension, patients were seated comfortably in a quiet environment for 5 min before beginning blood pressure measurements. Three blood pressure measurements were recorded, 1–2 min apart, and additional measurements only if the first two readings differed by >10 mmHg. We used a standard bladder cuff (12–13 cm wide and 35 cm long) for all patients and controls. End-diastolic elastance (Eed) was the ratio of left ventricular end-diastolic pressure (EDP) to LVEDV. We estimated EDP with a formula using the E/e' ratio (11.96 + 0.596 E/e') [31].We estimated mechanical energy including SW, PE, PVA, and LV mechanical efficiency [32]. (Figure 7).


**Figure 7.** Pressure-volume loops of the left ventricle (**left**). Measurement of parameters derived from a pressure-volume loop of the left ventricle (**right**). End-systolic elastance (Ees) represents the slope of the end-systolic pressure volume relationship (ESPVR) where ESP denotes end-systolic pressure, and Ees represents the noninvasively derived single-beat estimation of this parameter. LVEDV is the end-diastolic volume, and LVESV is the end-systolic volume. V0 is the intercept of the ESPVR at an end-systolic pressure of 0 mm Hg, and V100 is the point on the end-systolic pressure volume line at an end-systolic pressure of 100 mm Hg. Effective arterial elastance (Ea) represents the negative slope joining the end-systolic pressure volume point to the point on the volume axis at end-diastole, where SV represents stroke volume.

#### *4.3. Primary Study Endpoint: Major Adverse Cardiovascular Events (MACEs) during Follow-up*

The primary study endpoint was a composite endpoint of MACEs during follow-up. MACEs were defined by the occurrence of death for heart failure or hospitalization from CV causes (i.e., angina, myocardial infarction or heart failure). Angina and myocardial infarctions were defined according to ESC guidelines [33,34]. Two physicians (E.Z. and E.B.) blinded to 3DE findings reviewed all the medical records of included patients, regularly follow-up every 6 months—as per usual protocol at our Rheumatology Unit. In addition, further information were also obtained by evaluating hospital discharge cards and the personal status (i.e., alive/dead) that is recorded in the medical information system of our region.

#### *4.4. Statistical Analysis*

Continuous variables with no/mild skew were presented as mean ± SD; skewed measures were represented as median with first and third quartiles (Q1-Q3). Discrete variables were summarized as frequencies and percentages. The distribution of the data was analysed with a 1-sample Kolmogorov-Smirnov test. Categorical variables were compared by the χ2 test or the Fisher exact test as appropriate. Continuous data were compared using the 2-tailed unpaired t test (for normally distributed data sets) or the Mann-Whitney U test (for skewed variables). Time-dependent receiver operating characteristic curves were used to determine the optimal cutoffs for the primary composite endpoint based on the Youden index. Bivariate correlations were assessed by the Spearman coefficient (ρ). In unadjusted and multivariable-adjusted linear regression analyses, we expressed association between VAC and other clinical variables. Logistic regressions with odds ratios (ORs) and 95% confidence intervals (CIs) were applied to investigate associations between

VAC > 0.63 and clinical characteristics. Event rates are plotted in Kaplan-Meier curves for the primary composite end point and cardiovascular death, and groups were compared using the log-rank test. Univariate and multivariable Cox proportional hazards models were performed to identify the independent determinants of the primary composite end point. Variables with *p* < 0.05 at univariate analysis were included as covariables in multivariable models. Multivariable analyses were performed using a backward-conditional selection procedure on the remaining variables demonstrated a *p* value < 0.05. Pulmonary hypertension, dcSSc and interstitial lung disease, which have proven important in systemic sclerosis, were forced into the multivariable models, because model's adjustments should take into account factors with well-established clinical relevance. Moreover, VAC was introduced separately in the multivariable analysis to compare incremental value in predicting outcome. To assess the incremental value of VAC in addition to other risk factors for predicting adverse events, we calculated the improvement in global χ<sup>2</sup> value. Multivariable Cox models were discriminated by the C-index (values > 0.7 were deemed acceptable). The agreement between 2D-or 3D-echocardiography was tested by the Bland-Altman method and by the concordance correlation coefficient comparing the mean differences between the two methods of measurements and 95% limits of agreement as the mean difference. Intraobserver and interobserver reproducibilities of VAC were evaluated by linear regression analysis and expressed as correlation of coefficients (*r*) and standard error of estimates (SEE), and by the intraclass correlation coefficient. Reproducibility is considered satisfactory if the intraclass correlation coefficient is between 0.81 and 1.0. Intraobserver and interobserver reproducibility measurements were calculated in all 65 patients. All tests were two-sided and statistical significance was accepted if the null hypothesis could be rejected at *p* < 0.05. Data were analyzed with SPSS software version 24.0 (SPSS, Inc., Chicago, IL, USA). The study was approved by the institutional ethics committee.

#### **5. Conclusions**

In conclusion, our results may help better identify primary cardiac involvement in SSc. We provided the first evidence that VAC may be impaired in SSc and, importantly, that it seems to play a prognostic role in these patients. Our results also suggest that patients with dcSSc present an intrinsic LV systolic dysfunction, which seems to worsen over time and is responsible for the LV inability to compensate higher afterload. Further prospective studies are warranted to ascertain whether early intervention can improve outcomes in patients with "abnormal" VAC.

**Author Contributions:** Conceptualization, F.T. and E.Z.; data curation, F.T. and R.M.; investigation, D.M., E.B., E.D.Z., F.B., G.C.; resources, F.C.; supervision, S.I. and A.D. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Institutional Review Board Statement:** The study was conducted according to the guidelines of the Declaration of Helsinki, and approved by the Institutional Review Board (or Ethics Committee) of AOU of Padova (protocol number 3487/AO/15—13/7/2015 updated number 4895/AT/20— 23/7/2020).

**Informed Consent Statement:** Informed consent was obtained from all subjects involved in the study.

**Data Availability Statement:** The data sets used and/or analyzed during the current study are available from the corresponding author on reasonable request.

**Conflicts of Interest:** The authors declare no conflict of interest and have no known competing financial interests or personal relationships that may have influenced the work reported in this paper.

#### **References**


### *Article* **The Effect of Transcutaneous Vagus Nerve Stimulation in Patients with Polymyalgia Rheumatica**

**Jacob Venborg 1, Anne-Marie Wegeberg 2, Salome Kristensen 3,4, Birgitte Brock 5, Christina Brock 2,3 and Mogens Pfeiffer-Jensen 1,6,7,\***


**Abstract:** (1) Polymyalgia rheumatica (PMR) is an inflammatory disease characterised by pain, morning stiffness, and reduced quality of life. Recently, vagus nerve stimulation (VNS) was shown to have anti-inflammatory effects. We aimed to examine the effect of transcutaneous VNS (t-VNS) on PMR. (2) Fifteen treatment-naïve PMR patients completed the study. Patients underwent a 5-day protocol, receiving 2 min of t-VNS stimulation bilaterally on the neck, three times daily. Cardiac vagal tone (CVT) measured on a linear vagal scale (LVS), blood pressure, heart rate, patient-reported outcome, and biochemical changes were assessed. (3) t-VNS induced a 22% increase in CVT at 20 min after initial stimulations compared with baseline (3.4 ± 2.2 LVS vs. 4.1 ± 2.9 LVS, *p* = 0.02) and was accompanied by a 4 BPM reduction in heart rate (73 ± 11 BPM vs. 69 ± 9, *p* < 0.01). No long-term effects were observed. Furthermore, t-VNS induced a 14% reduction in the VAS score for the hips at day 5 compared with the baseline (5.1 ± 2.8 vs. 4.4 ± 2.8, *p* = 0.04). No changes in CRP or proinflammatory analytes were observed. (4) t-VNS modulates the autonomic nervous system in patients with PMR, but further investigation of t-VNS in PMR patients is warranted.

**Keywords:** polymyalgia rheumatica; vagus nerve stimulation; inflammatory response; PMR; t-vns

#### **1. Introduction**

Polymyalgia rheumatica (PMR) is an inflammatory rheumatic disease of unknown aetiology characterised by muscle pain and morning stiffness in the shoulders, pelvic girdle, and neck. PMR is rarely seen in persons below the age of 50, and can occur independently or alongside giant cell arteritis [1,2]. Typically, PMR will "burn out" after approximately 2 years and it is not associated with increased mortality [3–5]. Nevertheless, ordinary daily activities become immensely difficult and painful to accomplish; consequently, PMR patients often describe a great decline in quality of life. Finally, the disease is associated with increased usage of primary healthcare [6], and thus effective treatment restoring quality of life is of paramount importance to patients with PMR and their families. The first-choice treatment is systemically administered low doses (initially 12.5–25 mg/day) corticosteroids [7]. Although this treatment provides quick and efficient recovery, the adverse effects are typically numerous and severe [8]. Among these, osteoporosis, skin thinning, cushingoid appearance, weight gain, myopathy, and mood disorders are common [9]; as such, effective treatments with less negative and unwanted side effects are warranted. Biological anti-inflammatory drugs are frequently used within rheumatology. Recent studies

**Citation:** Venborg, J.; Wegeberg, A.-M.; Kristensen, S.; Brock, B.; Brock, C.; Pfeiffer-Jensen, M. The Effect of Transcutaneous Vagus Nerve Stimulation in Patients with Polymyalgia Rheumatica. *Pharmaceuticals* **2021**, *14*, 1166. https://doi.org/10.3390/ ph14111166

Academic Editors: Barbara Ruaro, Francesco Salton, Paola Confalonieri and Réjean Couture

Received: 15 August 2021 Accepted: 28 October 2021 Published: 16 November 2021

**Publisher's Note:** MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.

**Copyright:** © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

have demonstrated that PMR patients had increased serum levels of interleukin 6 (IL-6) in comparison with healthy controls, suggesting that IL-6 was part of the pathogenesis of PMR [10,11]. This is supported by the efficient use of monotherapy with IL-6 inhibitors in PMR patients [12–15]. However, treatment with biological drugs is still associated with side effects, such as the increased the risk of infection, fever, and rash.

It is generally accepted that the autonomic nervous system regulates neuro-immune communication primarily through the vagal nerve. In vitro studies have shown the inhibition of macrophage cytokine release in lipopolysaccharide-stimulated human macrophage cultures enriched with the cholinergic neurotransmitter acetylcholine [16]. Moreover, direct electrical stimulation of the vagus nerve in rats diminished serum levels of tumour necrosis factor-alpha (TNF-α) [17]. Vagal nerve stimulation (VNS) is also believed to diminish levels of pro-inflammatory cytokines, such as IL-1 and IL-6, the latter of which is of great interest in PMR patients [18]. In studies of healthy humans, transcutaneous vagus nerve stimulation (t-VNS) was shown to modulate the inflammatory response by increasing the cardiac vagal tone (CVT) and decreasing the systemic level of TNF-α [16,19]. Finally, t-VNS has reduced disease activity scores in patients with well-controlled psoriatic arthritis (PsA) and rheumatoid arthritis (RA) with no reported adverse effects [20,21]. However, a knowledge gap remains, as no studies have previously investigated the effect of t-VNS as an exclusive treatment in treatment-naïve patients with diseases characterised by high-grade inflammation.

Thus, we aimed to investigate the effect of 5-day t-VNS in treatment-naïve patients with PMR. We hypothesised that t-VNS would increase CVT and consequently reduce the inflammatory response, leading to clinical improvement in patients with PMR. Thus, the aims of this proof-of-concept study were to assess (1) the acute and 5-day CVT response to t-VNS; (2) the effect of 5-day t-VNS on cardiac-derived parameters, such as blood pressure (BP) and heart rate (HR); (3) the effect of t-VNS on inflammatory biomarkers; and (4) patient-reported inflammatory pain.

#### **2. Results**

Fifteen of the twenty enrolled patients completed the study. The baseline characteristics of the population are shown in Table 1. The intention-to-treat approach was used, and due to the investigation of various parameters, some datapoints may be missing in a subgroup of patients either because they were extreme values or because the assays were performed incorrectly. Consequently, such values were excluded from further analyses. No adverse events were reported. On average, each patient received 24 stimulations, which means they received fewer than planned (26).


**Table 1.** Demographic and General Population Characteristics.

Data are given as mean ± SD or no. (%) unless stated otherwise.

#### *2.1. Changes in Primary Outcome: Cardiac Vagal Tone*

One patient had faulty CVT recordings at all visits; consequently, these measurements were excluded. Another patient showed an extreme value of CVT on day 2; thus, this single measurement was excluded. Only measurements of CVT were excluded; the other parameters were not.

An acute 22% increase in CVT was observed 20 min after the initial t-VNS (3.4 ± 2.2 LVS vs. 4.1 ± 2.9 LVS, *p* = 0.02). However, no changes in CVT were observed on day 2 (3.4 ± 2.2 LVS vs. 3.9 ± 2.7 LVS, *p* = 0.50) nor on day 5 (3.4 ± 2.2 LVS vs. 4.2 ± 2.9, *p* = 0.20). The results are shown in Table 2.



Data are given as mean ± SD or median (interquartile range) unless otherwise stated. The *p*-values are a comparison between baseline and day 5. \* Comparison between baseline and 20 min.

#### *2.2. Changes in Secondary Outcomes*

#### 2.2.1. Changes in Cardiac-Derived Parameters

An acute decrease of 4 BPM in resting HR was observed 20 min after initial t-VNS (73 ± 11 BPM vs. 69 ± 9, *p* < 0.01). No changes in resting HR were observed on day 2 (73 ± 11 BPM vs. 74 ± 11 BPM, *p* = 0.77) or on day 5 (73 ± 11 BPM vs. 70 ± 14, *p* = 0.27). No changes in systolic or diastolic BP were observed 20 min after initial t-VNS, on day 2, or on day 5. The results are shown in Table 2 and Figure 1.

#### 2.2.2. Changes in CRP and Proinflammatory Analytes

Two patients were diagnosed obs. pro PMR but had no concomitant increase in markers of CRP; consequently, they were excluded from the analysis of changes in CRP. Furthermore, a single patient showed extreme values for CRP due to an infection and was excluded for analysis.

No changes in CRP were observed in response to t-VNS on day 2 (32.3 ± 19.7 mg/L vs. 32.4 ± 19.3, *p* = 0.94) or on day 5 (32.3 ± 19.7 mg/L vs. 35.9 ± 24.6 mg/L, *p* = 0.33) in comparison with the baseline. The results are shown in Table 2 and Figure 1. No changes were observed in any of the investigated analytes.

#### 2.2.3. Changes in Patient-Reported Outcome

A 14% reduction in the VAS score for the hips was shown on day 5 in comparison with baseline (5.1 ± 2.8 vs. 4.4 ± 2.8, *p* < 0.05). No significant changes were observed in MHAQ scores, VAS score of PMR influence, global VAS score, or duration of morning stiffness on day 2 or on day 5. The results are shown in Table 2 and Figure 1.

**Figure 1.** Raw data points, mean, and 95% CI of selected outcomes.

#### **3. Discussion**

To our knowledge, this is the first report of response to t-VNS in patients with PMR. We demonstrated that t-VNS caused an acute increase in CVT alongside a decrease in HR in treatment-naïve patients with PMR as a response to bilateral stimulation, indicating that an acute modulation of the autonomic nervous system was obtained. Furthermore, we demonstrated pain relief related to the hips in response to t-VNS.

In this study, we found lower mean values of CVT at baseline and on day 5 when compared with healthy individuals of similar age [22]. However, although this is the first preliminary report on CVT values in patients with PMR, it is consistent with low CVT values in patients with chronic pancreatitis and diabetes mellitus type 1 [23,24]. Furthermore, impaired parasympathetic activity has been demonstrated in patients with Crohn's disease [25]. Thus, our findings seem to support that the autonomic nervous system regulates neuro-immune communication and the activation of the cholinergic antiinflammatory reflex. A true increase in CVT following 5 days of stimulation may exist; however, this result may subsequently be hampered by the presence of a type 2 error due to low power.

PMR is a clinical diagnosis that may be difficult to establish with certainty due to the heterogeneity of the disease [26]. In 2012, The European League Against Rheumatism (EULAR) in collaboration with the American College of Rheumatology (ACR) developed provisional classification criteria for PMR in order to make the process of diagnosis more consistent [27]. However, these criteria are not meant for diagnostic purposes. Patients were eligible for inclusion if the doctor's putative diagnosis was PMR or obs. pro. PMR, and thus, the diagnoses were not definitive at the point of enrolment.

We observed a 14% decrease in VAS score of the pain related to the hips, and similar trends were shown for the rest of the parameters. This suggests that t-VNS might reduce pain. Furthermore, although PMR is not associated with increased mortality, patients with PMR typically describe an immense loss in quality of life. To evaluate the patient's selfreported function and quality of life, MHAQ score, VAS scores, and duration of morning stiffness were evaluated but were not altered in response to t-VNS.

We did not observe any decrease in the objective biochemical profile, including CRP and IL-6, which are of particular interest in PMR. This contrasts with findings in other inflammatory diseases, such as rheumatoid and psoriatic arthritis, where t-VNS resulted in decreased levels of CRP [21]. These contrasting findings may be due to the high-grade inflammation in PMR patients. Koopman et al. demonstrated inhibited levels of TNF-α and improved disease scores in response to VNS stimulation for 42 days with an implanted device in patients with RA, suggesting the long-term activation of the cholinergic antiinflammatory reflex [28]. In contrast, we applied stimulation three times per day over 5 days with a handheld, non-invasive device, and the treatment was mostly patientadministered. Thus, this study might underestimate the potential benefit of VNS on proand anti-inflammatory cytokines in PMR.

#### *Limitations*

This study is the first of its kind to investigate the effect of transcutaneous vagal nerve stimulation in patients with PMR characterised by high-grade inflammation. It is, however, an open-label, proof-of-concept study and thus has inherent limitations. First, as we did not have a sham control group, we cannot make firm conclusions on the observed changes in response to VNS. Second, as the study was open-label, all patients were aware of any beneficial effect and may have influenced subjective outcomes. However, all patients were examined by the same two researchers; thus, instructions on how to use the gammaCore were standardised, which minimised the risk of difference in the quality of the stimulation. Third, the study may be underpowered as we aimed to include 20 patients, but only 15 completed the protocol. Therefore, the sample size was small and vulnerable to inducing error. However, similar explorative pilot studies have been able to show differences in response to t-VNS in patient groups with established rheumatoid diagnoses [20,21]. Fourth, the intervention length of 5 days may have been insufficient for t-VNS to alter the disease activity. However, as these patients were treatment-naïve and suffered from pain, we did not believe it ethical to prolong this explorative treatment. Consequently, all patients in the study went on to be treated with prednisolone. Nonetheless, we cannot rule out the possibility that a longer intervention might have produced pronounced effects. Fifth, it has been questioned whether 5 min CVT was a reliable biomarker of parasympathetic activation, but the measure has been shown to perform better than heart rate variability measures [29]. Lastly, with only three out of the total 26 stimulations being supervised, we could not ensure the quality of each stimulation.

#### **4. Materials and Methods**

#### *4.1. Study Design*

This study was an open-label, proof-of-concept experimental pilot study investigating the effect of t-VNS in patients with inflammatory diseases. Two centres were used for inclusion: Mech-Sense, Aalborg University Hospital, and Department of Rheumatology, Aarhus University Hospital. A 5-day protocol was used, which was believed to be of adequate length to demonstrate our hypothesis, but did not unnecessarily delay treatment with glucocorticoids.

#### *4.2. Cohort*

Forty-two patients did not meet any exclusion criteria and were eligible for screening by a trained doctor to confirm the diagnosis of either (1) a well-established diagnosis of PMR (certain diagnosis) or (2) a putative PMR diagnosis, where no alternative pathology could explain the case better (obs. pro PMR). Exclusion criteria were any corticosteroid treatment within 5 weeks prior to inclusion, age < 18 years, known cardiovascular disease, hypotension (<100 mmHg systolic and <60 mmHg diastolic), pregnancy (positive U-HCG) or current lactation, and non-compliance with the protocol. Inclusion criteria were newly diagnosed, treatment-naïve PMR patients. No drugs were used besides NSAIDs and paracetamol; while the usage of NSAIDs during the protocol was not disallowed, it was recommended that patients did not use it.

If the eligible patients agreed to participate, they signed an informed consent form. Twenty patients were included; however, 5 patients dropped out before completion, leaving 15 patients for analysis. Reasons for drop-out were: non-compliance with the protocol (n = 1), withdrawal of consent (n = 2), and did not show (n = 2).

#### *4.3. Vagus Nerve Stimulation*

t-VNS was performed using a non-invasive, handheld gammaCore® device (electroCore, Inc., Basking Ridge, NJ, USA) providing transcutaneous low-voltage electric stimulation on the cervical part of the vagus nerve. The signal consisted of five 5000 Hz sine-wave pulses repeated at a rate of 25 Hz. Patients were given clear instructions to place the two gel-covered conductors on top of the common carotid arteries on the neck. The amplitude of the electric signal, ranging from 0 to 40 on an arbitrary scale, could be adjusted via two control buttons on the device. Each stimulation lasted 2 min, after which the device would stop automatically.

On days 1–4, stimulations were carried out bilaterally three times a day (morning, noon, and evening), while on day 5 only one stimulation was carried out. A total of 26 stimulations were planned for each patient. Compliance was assured by counting the remaining stimulations when the device was returned. The patients were given clear instructions to position the device correctly, and the amplitude was to be slowly increased until a mild contraction of the ipsilateral oral commissure was seen or the pain from the stimulation was unbearable. At the second visit, the patients performed a stimulation under the supervision of the investigator to ensure safe and proper usage.

#### *4.4. Outcomes*

#### 4.4.1. Primary Outcome: Resting Cardiac Vagal Tone

The primary outcome was a change in resting CVT between baseline and day 5 (longterm response) and differences between baseline and 20 min after the first stimulation (acute response).

CVT is a non-invasive measure of the efferent parasympathetic cardiac vagal tone, which is computed from a five-minute ECG recording; incoming QRS complexes are compared with a template derived from the initial part of the recording, and changes in R–R intervals are detected via phase shift demodulation [22]. CVT was measured on a linear vagal scale where 0 represents full atropinisation [30]. Resting CVT was assessed via a three-lead ECG (eMotion Faros180◦ portable cardiac monitoring device, Bittium, Oulu, Finland) using Ambu BlueSensor P ECG-electrodes (Ambu, Copenhagen, Denmark), placed on cleaned and dried skin, and assessments were performed in conformity with international recommendations [31]. The recordings were analysed using ProCVT software (ProBiometrics, London, UK) to derive CVT.

On days 1, 2, and 5, five-minute ECG recordings were conducted. On day 1, two recordings were made to evaluate the acute response; one prior to the first stimulation (baseline) and the second after 20 min. On days 2 and 5, a single CVT recording was performed before stimulation. The successful recordings were manually edited if needed, i.e., changes in HR exceeding 15 beats per minute (BPM) between two consecutive heartbeats were treated as artefacts, e.g., coughing or sudden movements. If artefacts were present in the data, the five heartbeats before and after were discarded by the underlying algorithm. 4.4.2. Secondary Outcomes: Cardiac-Derived Parameters, CRP, Proinflammatory Analytes, and Patient-Reported Outcome

Patient-reported outcomes were assessed on days 1, 2, and 5, with each patient completing two questionnaires. Firstly, the modified health assessment questionnaire (MHAQ), which consists of eight questions measuring the ability to perform common daily life activities, such as dressing, arising, eating, walking, hygiene, reaching, and gripping. Each patient was asked to rate their ability to perform these activities on a scale ranging from 1 to 4: 1 = without difficulty, 2 = with some difficulty, 3 = with much difficulty, and 4 = unable to do the requested task. The second questionnaire consisted of three assessments on a validated continuous (0–100 mm) visual analogue scale (VAS scoring) and an evaluation of the duration of morning joint stiffness. For the VAS score, three domains were assessed: (1) general pain, (2) pain related to the hips, and (3) a general, overall assessment of the negative effect and influences caused by PMR.

Measurement of BP and HR was carried out prior to each ECG recording. Each measurement was performed on the upper left arm using an electronic sphygmomanometer (UA-852; A&D Company, Limited, Tokyo, Japan).

Blood samples were drawn on days 1, 2, and 5 prior to other measurements. Samples for routine clinical biochemistry, alongside EDTA-plasma and serum, were drawn on baseline day and day 5 for analysis of proinflammatory analytes IFN-γ, IL-,1β, IL-2, IL-4, IL-6, IL-8, IL-10, IL-13, and TNF-α. Analyses of cytokines were performed via Luminex multiplexing technology using the Inflammation 20-Plex Human ProcartaPlex™ Panel (Invitrogen, Thermo Fisher Scientific, Waltham, MA, USA) and a MAGPIX instrument (Luminex, Austin, TX, USA) in accordance with the manufacturer's protocol. For each analyte, extreme outliers, defined as values above Q3 + 3 × IQR or below Q1 − 3 × IQR, were identified and removed.

#### *4.5. Statistical Methods*

Data were presented as mean ± standard deviation (SD) unless otherwise clarified. All data were evaluated for normality using Shapiro–Wilk test for normality or through visual inspection of QQ plots. For statistical comparison between baseline and visit values, paired *t*-test was used for data of normal distribution, and Wilcoxon signed-rank test was used for data of non-normal distribution. A *p*-value less than 0.05 was considered significant. All data analyses were performed in STATA version 16.0 (StataCorp, TX, USA) and R version 4.0.3 (The R Foundation for Statistical Computing). Likewise, all graphical outputs were produced using the same version of R.

#### **5. Conclusions**

In conclusion, we showed an acute modulation of the autonomic nervous system in patients with PMR as evidenced by increased CVT and decreased HR. Furthermore, we showed alleviation of hip pain in response to a five-day protocol, but this was not reflected in the cytokine profile. Further investigation of t-VNS in PMR patients is warranted, preferably in blinded, randomised, sham-controlled trials, before any firm conclusion is drawn upon the ability to activate the cholinergic anti-inflammatory reflex in this patient group.

**Author Contributions:** Conceptualization, B.B., C.B., M.P.-J.; Methodology, B.B., M.P.-J.; Validation, A.-M.W., B.B., C.B., M.P.-J.; Formal analysis, J.V., C.B.; Investigation, J.V., A.-M.W., S.K.; Data curation, J.V., A.-M.W., C.B.; Writing—original draft preparation, J.V.; Writing—review and editing, J.V., A.- M.W., S.K., C.B., M.P.-J.; Visualization, J.V., C.B.; Supervision, A.-M.W., M.P.-J.; Project administration, B.B., C.B., M.P.-J.; Funding acquisition, J.V., M.P.-J. All authors have read and agreed to the published version of the manuscript.

**Funding:** J. Venborg was financially supported by the Danish Rheumatism Association.

**Institutional Review Board Statement:** The study was conducted in conformity with the Good Clinical Practice Unit (CPMP/ICH/135/95) and approved by the Central Denmark Region Committees on Health Research Ethics (1-10-72-199-16), the Danish Data Protection Agency (1-16-02-442-16), the

Danish Medicines Agency (2016024373), and the European Databank on Medical Devices (CIV-16-03- 015125).

**Informed Consent Statement:** Informed consent was obtained from all subjects involved in the study.

**Data Availability Statement:** Data is contained within the article.

**Acknowledgments:** The gammaCore devices used for intervention were supplied by electroCore, Inc. The authors would like to thank the Department of Clinical Biochemistry, Aarhus University Hospital, for carrying out the blood samples analyses. Additionally, a special thank goes out to all participating patients for making the project possible.

**Conflicts of Interest:** The authors declare no conflict of interest.

#### **References**


### *Review* **Respiratory Manifestations in Systemic Lupus Erythematosus**

**Salvatore Di Bartolomeo 1, Alessia Alunno <sup>2</sup> and Francesco Carubbi 3,\***


**Abstract:** Systemic lupus erythematosus (SLE) is a chronic systemic autoimmune disease characterized by a wide spectrum of clinical manifestations. The respiratory system can be involved in up to 50–70% of patients and be the presenting manifestation of the disease in 4–5% of cases. Every part of the respiratory part can be involved, and the severity can vary from mild self-limiting to life threatening forms. Respiratory involvement can be primary (caused by SLE itself) or secondary (e.g., infections or drug toxicity), acute or chronic. The course, treatment and prognosis vary greatly depending on the specific pattern of the disease. This review article aims at providing an overview of respiratory manifestations in SLE along with an update about therapeutic approaches including novel biologic therapies.

**Keywords:** systemic lupus erythematosus; airway disease; interstitial lung disease; shrinking lung syndrome; diffuse alveolar hemorrhage; pleurisy; infection

**1. Introduction**

Systemic lupus erythematosus (SLE) is a chronic, systemic autoimmune disease with a relapsing–remitting course and characterized by the production of a wide range of autoantibodies. Although people of any age and gender can be involved, females of childbearing age are the most affected, with a female-to-male ratio of about 9:1 [1].

SLE can have a wide range of manifestations, involving virtually every organ or apparatus, and its severity can vary from very mild disease without major organ involvement, to severe life-threatening conditions. Clinical manifestations may include cytopenia, fever, malar and other skin rashes, oral ulcers, polyarthralgia/non erosive arthritis, vasculitis, renal, neurological, cardiac and pleuro-pulmonary involvement [2–4]. Recently, a new set of classification criteria was proposed by American College of Rheumatology/European League Against Rheumatism (ACR/EULAR), designed to increase classification sensitivity and specificity for inclusion in SLE research studies and trials [5]. Furthermore, recommendations on disease management from EULAR were recently updated [6,7].

SLE pathogenesis is multifactorial and not completely understood, and includes an interaction between non-Mendelian genetic predisposition, hormonal and environmental factors, ultimately leading to an alteration in both innate and adaptive immunity. In particular, SLE pathogenesis is characterized by an impaired apoptotic cell clearance by phagocytes, B-cell and T-cell autoreactivity leading to an abnormal production of autoantibodies, and immune complexes (ICs) formation with nuclear and cytosolic antigens. ICs can, in turn, activate the classical pathway of the complement system contributing to inflammation and damage in target organs [4,8].

Although the exact prevalence is unknown, respiratory tract involvement can be present in 50–70% of SLE patients, being the presenting symptom of the disease in 4–5% of cases and more frequent in men [8–10]. Every part of the respiratory tract can be involved:

81

**Citation:** Di Bartolomeo, S.; Alunno, A.; Carubbi, F. Respiratory Manifestations in Systemic Lupus Erythematosus. *Pharmaceuticals* **2021**, *14*, 276. https://doi.org/10.3390/ ph14030276

Academic Editor: Barbara Ruaro

Received: 28 January 2021 Accepted: 16 March 2021 Published: 18 March 2021

**Publisher's Note:** MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.

**Copyright:** © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

upper and lower airways, vessels, pleura, lung parenchyma and respiratory muscles (Figure 1). Respiratory manifestations can be acute or chronic, primary (directly caused by the disease) or secondary (due to concomitant complications such as infections). Interestingly, acute manifestations may be associated with generalized lupus disease activity, while chronic complications may progress independently to general disease activity [10].

**Figure 1.** Overview of respiratory manifestations in systemic lupus erythematosus along with the prevalence and corresponding references.

Respiratory manifestations of SLE are associated with a variable mortality rate, depending to the type of involvement, its extension, and the presence of comorbidities. In particular, pulmonary involvement is associated with higher mortality and with negative effect on patient-reported outcomes, patient-performed outcome and quality of life [11]. Unfortunately, clinical and therapeutic trial data specifically focused on respiratory manifestations of SLE are scarce, so treatment options are based on evidence from other organ involvement in SLE, or from respiratory manifestations in other autoimmune diseases, or based on case reports or small cases series.

In this review, we provide an overview of the scientific literature about the respiratory involvement in SLE, and highlight the progress achieved so far in the understanding of pathogenic mechanisms and in the identification of therapeutic strategies needing to be addressed in future studies. In particular, we designed a comprehensive literature search on this topic, by a review of reported published articles in indexed international journals up until 31st October 2019, following proposed guidelines for preparing a biomedical narrative review [12].

#### **2. Airway Disease**

Laryngeal involvement can occur in 0.3–30% of SLE patients and range from asymptomatic to severe life-threatening upper airway obstruction [13]. Clinical manifestations are non-specific and include hoarseness, cough, dyspnea, and stridor. Mucosal inflammation with erythema and edema is the major manifestation; other findings include vocal cord

paralysis, bamboo nodes of the vocal cords, recurrent laryngeal neuropathy, epiglottitis, rheumatoid nodules [14], vasculitis, inflammatory mass formation and late subglottic stenosis. It usually responds well to corticosteroids (CS) therapy. However, in severe cases of respiratory failure, advanced airway management may be necessary [13,15,16].

Other airway involvement includes upper airway angioedema, necrotic tracheitis and early post-intubation stenosis, bronchial stenosis; small airway obstruction with bronchiolitis is found in the 13% to 21% of patients with the use of high-resolution computed tomography (HRCT) [17] and bronchiectasis as a consequence of direct SLE involvement or as sequelae of bronchopulmonary infections [17–21].

Using pulmonary function tests (PFTs), Andonopoulos et al. found a prevalence of obstructive disorders in 6% of SLE patients and 0% of control group (smokers were excluded) and initial damage of small airways (defined as maximum expiratory flowvolume (MEFV) 25–75 below 60% of predicted value) was present in 24% of SLE patients but the difference was not statistically significant with the control group [22], moreover, surveillance of pulmonary function tests revealed a progressive decline in values indicating small airways damage with time [17].

#### **3. Parenchymal Lung Disease**

#### *3.1. Acute Diseases*

Acute lupus pneumonitis (ALP) and diffuse alveolar hemorrhage (DAH) are acute and uncommon manifestations of SLE [10].

#### 3.1.1. Acute Lupus Pneumonitis

ALP is a rare, probably under-recognized, manifestation of SLE that occurs in 1–8% of SLE patients, in particular younger patients and patients with a recent diagnosis. Moreover, it can be the first manifestation of a previously unrecognized SLE in 50% of cases [10,17,23–25]. Clinical presentation is non-specific and can simulate infectious pneumonia with sudden onset of fever, cough, dyspnea, pleuritic chest pain and occasionally hemoptysis. Physical examination can reveal tachycardia, tachypnoea hypoxemia, hypocapnia and lung crackles. Occasionally, it can present with acute respiratory failure requiring mechanical ventilation. ALP has been described complicating SLE during pregnancy [10,17,23–26]. Chest X-ray can show multiple, bilateral patchy infiltrations, predominantly in the lower lobes, with or without pleural effusion. However, chest X-ray can be normal, especially in the initial phases or shows only lung nodules. Although these findings are non-specific, CT scan can show ground glass opacities and areas of consolidation, predominantly in the lower lobes [10,23]. Histologically, ALP presents diffuse alveolar damage (DAD) with inflammatory cell infiltration, damage and necrosis of alveolar-capillary unit, edema, hyaline membrane formation and alveolar hemorrhage. Capillaritis and thrombosis have also been described. Alveolar damage may be mediated by the deposition of ICs and complement fractions. However, there are not diagnostic and/or pathognomonic findings specific for ALP. Some data highlight a pathogenetic role of anti-Ro/SSA antibodies, due to an association between ALP and these autoantibodies [10,17,23–26]. Since there are no specific clinical or imaging findings in ALP, the diagnosis is of exclusion and a comprehensive differential diagnosis must be considered with infections, organizing pneumonia, malignancy, DAH, pulmonary edema, lung drug toxicity [23,24]. Infections must always be ruled out, since they may have a similar clinical picture and immunosuppressive treatments needed to treat ALP, could have a deleterious effect on the infection course. In this setting, bronchoscopy with bronchoalveolar lavage fluid (BALF) analysis should be performed and followed by microbiological tests for common and opportunistic pathogens [23]. It seems that the presence of eosinophilia or neutrophilia on BALF carries worse prognosis than lymphocytosis. A marked elevation in C-reactive protein (CRP) and procalcitonin levels in the serum may suggest an infection. Lung biopsy is rarely necessary [23,24,27]. Prognosis is severe, with a high mortality risk; in particular, Matthay et al. reported a mortality rate of 50% among 12 patients treated

for ALP [28] while more recently Wan et al. found a mortality of 40% [29]. High doses of CS are the mainstay of treatment. In severe cases daily pulses of methylprednisolone (up to 1000 mg/day for 3 days) can be used, followed by 1–2 mg/kg per day of prednisone and a subsequent tapering according to clinical response. Immunosuppressants such as cyclophosphamide (CYC) and azathioprine, biologics drugs such as rituximab (RTX), intravenous immunoglobulins (IVIg) or plasma exchange can be added in severe refractory cases, but the evidence on their efficacy is scarce. A broad-spectrum antibiotic coverage should be started until an infection is ruled out, and then prophylaxis against opportunistic pathogens (e.g., Pneumocystis jirovecii) can be considered during immunosuppressive treatment [10,17,23–25,28,29]. Factors that seem to contribute to poor outcome include intercurrent infections, aspiration, diaphragmatic dysfunction, cardiac and renal failure, drug and oxygen toxicity [7,29–31]. Of those who recover from the acute episode, 50–100% may eventually develop chronic interstitial pneumonia so a thorough follow-up is advisable [10,31].

#### 3.1.2. Diffuse Alveolar Hemorrhage

DAH, first described by Dr. William Osler in 1904, is a rare, but very severe and potentially fatal complication of SLE [8,32]. It is not exclusive to SLE, occurring in several other conditions such as anti-neutrophil cytoplasmic autoantibody (ANCA)-associated vasculitis, antiphospholipid syndrome (APS), other connective tissue diseases, infections, bone marrow transplantation, and drug toxicity [33,34].

DAH prevalence among SLE patients ranges from 0.5–0.6% to 5.4–5.7% with a femalto-male ratio of approximately 6:1. DAH was described as initial manifestation of SLE in 11–20% of cases; some autoptic studies in SLE patients have found the presence of red blood cells in the lungs of 30–66% of cases maybe due to the presence of either unidentified or subclinical, paucisymptomatic forms of DAH [10,33]. Mean age of presentation is 27 years, but it can occur at an early stage of the disease [17]. Some patients may have recurrent episodes [33,35].

The clinical picture of DAH is characterized by the sudden onset, within hours or a few days, of dyspnea, hypoxemia with possible acute respiratory failure and need for mechanical ventilation in more than 50% of cases, fever, cough, hemoptysis with a rapid fall in hemoglobin levels, and appearance of new alveolar or interstitial infiltrates. Some patients can present chest pain. Hemoptysis can be of variable severity, dramatic in some cases, or initially absent in up to 33% of cases [8,10,33,36].

Chest X-ray can be normal or show bilateral, rarely unilateral, airspace opacities (patchy, focal or diffuse). CT scan may show diffuse, bilateral and patchy alveolar infiltrates, also asymmetrical, ground glass opacities or diffuse nodular opacities and it is more accurate than chest X-ray to evaluate the extent of the disease. BALF is usually hemorrhagic, and the presence of 20% or more hemosiderin-laden macrophages in BALF is a criterion for DAH diagnosis [8]. However, this pattern can appear only after 48–72 h from symptom onset. BALF culture is mandatory to exclude an infection as a cause of DAH; many pathogens such as Legionella pneumophila, Strongyloides stercoralis and Cytomegalovirus can be associated with DAH [8]. Secondary infections, mainly nosocomial, can complicate the course of DAH thereby worsening the disease prognosis. Zamora et al. found a mortality rate of 100% in 3 patients with secondary infections (1 infected with Aspergillus, 1 with Escherichia coli and 1 with both methicillin-resistant Staphilococcus aureus and Candida) [37]; in a study by Rojas-Serrano et al., bronchoscopic assessment performed during the first 48 h of admission in 13 SLE patients demonstrated infections in 57% of cases including Pseudomonas aeruginosa, Serratia marcescens, Citrobacter freundii, and Aspergillus fumigates [38].

Lung biopsy is rarely necessary, and critically ill patients might not tolerate this invasive procedure. Histologic findings are non-specific with the presence of mild blood extravasation. More severe cases present capillaritis with neutrophil infiltration of alveolar septa [8,10,33,35,36]. Laboratory findings can show a rapid drop in hemoglobin levels, along with other characteristics of an active SLE, such as low complement levels, thrombocytopenia and autoantibodies. A rapid fall in hematocrit levels must alert clinicians to DAH [8]. An increase of carbon monoxide diffusing capacity (DLCO) of 30% or more over baseline values or an absolute elevation over 130% of predictive value is supportive to the diagnosis of DAH, due to the enhanced uptake of carbon monoxide by hemoglobin present in the alveoli [8,10,39].

DAH pathogenesis is not completely known, but it is characterized by an immune mediated damage of small vessels and alveolar septa, with deposition of ICs and complement fractions in the alveolar capillaries. A neutrophil interstitial infiltration with alveolar and capillary walls necrosis (capillaritis) has also been demonstrated. Neutrophils may play a pathogenetic role by the release of neutrophils extracellular traps (NETs) and cytotoxic proteins that contribute to the local damage. The loss of integrity of the alveolarcapillary wall results in the leakage of red blood cells into the alveolar space [8,10,36]. Other proposed mechanisms include: increased apoptosis of the alveolar wall cells with monocyte-macrophage infiltration, diffuse alveolar damage with edema of alveolar septa and formation of hyaline membranes, and fibrinoid necrosis. B-lymphocytes may play a pivotal role in autoantibodies formation [8,36].

Risk factors for the development of DAH include: history of thrombocytopenia, low C3 fraction, high titers of anti-double-stranded (ds)DNA, leucopenia, coexisting neuropsychiatric lupus, high disease activity (e.g., SLE Disease Activity Index (SLEDAI) score >10) and the presence of active renal disease (in particular class III and IV lupus nephritis) [8,10,36].

DAH treatment is based on case reports, expert opinion or derived from other conditions [36]. The treatment's mainstay is the early administration of high dose iv methylprednisolone (usually 1 g/day iv for 3 or more days up to 4–8 g total dose) with subsequent tapering according to clinical evolution. CYC can be added in severe forms but data on its efficacy are contrasting with an increased mortality in the study of Zamora et al. [37], when compared to the beneficial effect in the study of Sun et al. [40]. However, a recent meta-analysis did not confirm an association with CYC and survival [41]. Other immunosuppressants have been used, such as cyclosporine, azathioprine, tacrolimus, mycophenolate mofetil (MMF), without any conclusive evidence. Among biologic drugs, RTX has shown some good results and different schemes and dosages has been used, mainly 375 mg/m<sup>2</sup> weekly × 4 or fortnightly × 2 or 1 g 2 weeks apart, generally in association with CS. In the majority of reports, one course of therapy was sufficient; however, in refractory cases, maintenance therapy with RTX can be needed [8,36,42–46]. The potential role of belimumab remains unknown [8,36].

Plasmapheresis is generally used in patients with refractory and more severe disease, with contrasting results in literature [41]. Adverse events can occur in up to 10% of cases, are more frequent in the first procedure and are generally mild or moderate, including access site or device problems, hypotension and syncope, tingling, urticaria, nausea/vomiting, chills, fever, arrhythmia [47].

Other therapeutic options include IVIg, intrapulmonary administration of recombinant factor VIIa, and umbilical cord mesenchymal stem cell transplantation [36]. Supportive and resuscitative treatments must be guaranteed, in particular in the context of respiratory failure in which patients may require mechanical ventilation up to extracorporeal membrane oxygenation support in more severe cases. Broad spectrum antimicrobic therapy is mandatory, since infections can both initiate or complicate the course of DAH [8,36].

Prognosis is poor, with a mortality rate of up to 70–92%, (average 50%); however, a trend in the reduction of mortality was observed in the recent years, likely due to a better knowledge of the disorder, a more rapid diagnosis and a precocious introduction of novel, targeted therapies [8]. Older age, longer lupus disease duration, acute massive hemoptysis, requirement of mechanical ventilation and plasmapheresis treatment, thrombocytopenia (not universally accepted) and infections are associated with an increased risk of mortality [8,10,41]. However, severe diseases rendered the requirement of plasmapheresis treatment and mechanical ventilation are themselves associated with poor outcome. The

presence of other comorbidities must also be considered. Among survivors, 70–90% can eventually develop pulmonary fibrosis therefore a strict follow-up is mandatory [10,41]. Randomized trials of therapeutics are needed to determine the most efficacious strategies for SLE-associated DAH for better management of this life-threatening complication.

#### *3.2. Chronic Diseases*

Chronic interstitial lung disease (ILD) in SLE seems to be less frequent in comparison to other connective tissue diseases (CTDs), and it is rarely severe [10,48–50]. The exact prevalence is probably underestimated, because older studies performing chest X-ray have shown the presence of ILD in 6–24% of SLE patients, while in those using a more sensitive method such as HRCT, ILD was found in up to 70% of cases, suggesting that the condition is frequently subclinical [10,49,51]. Risk factors for ILD include older age, late-onset SLE, illness duration (≥1 year), tachypnea, low levels of anti-dsDNA, high level of C3 and male gender [48–52]. The presence of Raynaud's phenomenon, swollen fingers, sclerodactyly, telangiectasia, nailfold capillary abnormalities among SLE patients was associated with a higher prevalence of restrictive deficit and reduced DLCO, probably in the context of overlap syndromes that seem to carry a worse lung prognosis. Some associations were found with anti-U1 RNP, anti-SSB, anti-Scl70 and anti-SSA antibodies and sicca syndrome [10,49–53].

The most common pattern, histologically and radiologically, is non-specific interstitial pneumonia (NSIP); however, usual interstitial pneumonia (UIP) is not uncommon [52]. Lian et al. reported that the most frequent findings were ground glass opacities (84.4%), followed by consolidation (21.1%), honeycombing (15.6%), and traction bronchiectasis (12.8%) [53].

Clinically, ILD can evolve as a consequence a disease with acute onset (ALP or DAH) or follow a more insidious onset with chronic non-productive cough, exertional dyspnea and non-pleuritic chest pain. The mean age of onset is earlier when following an acute condition (mean 38 years) compared to the chronic form (46 years). Patients with a radiologically documented ILD can also be asymptomatic [10,51]. Inspiratory fine crackles may be heard upon physical examination, while the presence of digital clubbing is rare. Pulmonary function tests can show a restrictive pattern with reduced DLCO [10]. The severity of ILD does not correlate with SLE serologic markers [49].

Prognosis for SLE-associated ILD seems more favorable when compared to idiophatic pulmonary fibrosis or RA-associated ILD [50,52,54,55]. Toyoda et al. found a five-year survival rates of 92.9% calculated from the time ILD was diagnosed and the survival rate did not significantly differ between the patients with and without ILD [52].

Lymphocytic interstitial pneumonia (LIP) can complicate many autoimmune conditions and has been described in SLE patients in particular when associated with Sjögren's Syndrome. LIP is characterized by the formation of lung cysts, an infiltration of the interstitium with polyclonal lymphocytes and lymphocytic alveolitis [10,49,56,57]. Prognosis is variable. Approximately 50–60% of patients respond to corticosteroids with stabilization or improvement of the disease, but in others there is progressive decline in pulmonary function and development of honeycomb lung. In general, death occurs in approximately 33 to 50% of patients within 5 years of diagnosis [56,57].

Organizing pneumonia (OP) has also been described as initial manifestation of SLE and regardless of SLE activity [10,49,58–60]. On HRCT, OP shows ground glass opacities, consolidations and peribronchovascular opacities. OP has also been described in rhupus syndrome [61]. CS are the treatment of choice. In the majority of cases patients recover within days of weeks after treatment introduction and radiographic findings show improvement in 50–86% of patients. Spontaneous resolution may occur. However, in a minority of cases, the disease may persist, and up to 30% may have a relapse after treatment withdrawal [62]. Several immunosuppressant agents, such as azathioprine, MMF, cyclosporin, CYC and plasmapheresis, have been used in various case reports. [58–62]. Finally, an association between SLE and pulmonary sarcoidosis has been described [10,63–66]. According

to Rajoriya N et al., patients with sarcoidosis have an OR of 8.33 (2.71 to 19.4) for the development of SLE [64].

Placebo-controlled trials to guide the treatment of SLE-associated ILD are lacking. CS are, generally, the mainstay of treatment and patients usually show a good response. Immunosuppressants such as CYC, azathioprine, or MMF can be added in refractory more severe cases [10,23]. Among biologics, RTX can be used in some cases [67].

Treatments are generally well tolerated; with CYC, immuno- and myelosuppression, as well as IgG levels decreased can occur with subsequent infections that are generally non-life-threatening and do not necessitate stopping treatment [68,69]. In particular, in the study of Okada et al., only two sessions of CYC infusions among a total of 141 were postponed because of upper respiratory infections [69]. Interestingly, cumulative data show a higher frequency of adverse events, including hemorrhagic cystitis, premature ovarian failure, herpes zoster and cancer, with the oral administration, in comparison with pulse intravenous infusion of CYC, as found in the lupus nephritis [68–70]. Concerning the use of MMF in SLE-ILD, only one of ten patients with CTD-ILD had a diagnosis of SLE in the case series by Saketkoo et al. [71], while Fisher et al. included four patients with SLE-ILD in their retrospective study [72]. The most common side effects reported in these studies were diarrhea and leucopenia.

#### **4. Vascular Diseases**

#### *4.1. Acute Reversible Hypoxemia Syndrome*

First described in 1991 by Abramson [73], acute reversible hypoxemia syndrome is characterized by the acute onset of dyspnea, chest pain and hypoxemia. Pleural involvement may be present. It is frequently associated with a flare of SLE. Pulmonary imaging is generally normal, while PFTs may show reduction in vital capacity and DLCO [17,51]. Pathophysiology is not completely understood. An association between endothelium activation, with a high expression of vascular adhesion cell molecule-1 (VACM-1) and intercellular adhesion molecule-1(ICAM-1), and activated neutrophil and platelet sludging mediated by complement activation has been postulated as a pathogenic mechanism. These alterations can ultimately lead to endothelial dysfunction, vascular lumen occlusion by leukocyte aggregates and subsequent hypoxemia [17,51,73,74].

This condition rapidly responds to low doses of CS, usually insufficient to control SLE flares, when present together, so higher doses may be needed. Combination of high doses of aspirin can be useful [17,51], and most cases respond to therapy with rapid improvement of gas exchanges [9].

#### *4.2. Pulmonary Embolism*

SLE patients are at increased risk of developing deep vein thrombosis (DVT), occurring in up to 10% of patients [75], and pulmonary embolism (PE) with a 3-fold increased risk in comparison to general population [76]. Vein thromboembolism (VTE) represents the third most common cardiovascular (CV) event after myocardial infarction and stroke [77,78]. PE has a high mortality rate of up to 15%. Many risk factors have been investigated besides "classical" risk factors such as obesity, hyperglycemia and hyperlipidemia [77]. Moreover, You et al. found the following risk factors associated with PE: high body max index, hypoalbuminemia, positivity for anti-phospolipid antibodies (aPL), high levels of high sensitivity CRP and high doses of CS (>0.5 mg/kg/day) [78]. Finally, SLE patients with APS are at increased risk of DVT and PE. The prevalence of APS among SLE patients is about 30% [79].

APS can cause a hypercoagulable state by interacting and activating platelets, neutrophils and endothelial cells [78]. In particular, a metanalysis found that SLE patients with APS have a six times greater risk of developing PE than SLE patients without APS [79]. Moreover, patients with the positivity for lupus anticoagulant (LA) and high titers of IgG anti-cardiolipin (aCL) are at increased risk [80,81].

Clinical manifestations depend on the severity of vasculature occlusion, ranging from asymptomatic small vessels occlusion to massive PE with sudden right ventricular failure and acute circulatory collapse. Other symptoms of PE include pleuritic chest pain, dyspnea, hemoptysis, crepitations, tachypnea and tachycardia. Chronic PE can progress to secondary pulmonary arterial hypertension (PAH) due to the reduction of pulmonary vascular tree [49]. In addition to PAH, other non-thrombotic intrathoracic manifestations of APS associated with SLE are: DAH, adult respiratory distress syndrome (ARDS) and valvular heart disease (e.g., Libman-Sacks endocarditis) [49,82]. A rare, potentially fatal, manifestation of APS is the catastrophic APS (CAPS). CAPS is characterized by the diffuse occlusion of small vessels in three or more organs [81–85]. It generally develops in APS patients in association with a trigger such as infections, neoplasm or surgery. Respiratory failure is often present and can rapidly progress to acute respiratory distress syndrome (ARDS) [81–85].

Treatment of APS includes anticoagulation with the vitamin K antagonists (VKA), to maintain an international normalized ratio (INR) range of 2.0 to 3.0, for a definite period in a first provoked episode, indefinitely in recurrent episodes or in patients with a high-risk profile [81,85]. In patients with recurrent arterial or venous thrombosis, a higher INR range 3.0–4.0 or the addition on low dose aspirin should be considered. Common CV risk factors should be corrected, concurrently. In high-risk anti-phospholipid antibodies (aPL) carriers without history of thrombosis, prophylactic treatment with low dose aspirin can be adopted [81,85]. Hydroxychloroquine may reduce thrombotic risk both in APS and non-APS SLE patients due to its pleiotropic effects but evidence in this regard is still scarce [78,85]. Treatment of CAPS includes: elimination of triggers (e.g., infections), combination therapy with heparin, glucocorticoids and plasma exchange or intravenous immunoglobulins. B-cell depletion (e.g., RTX) or complement inhibition (e.g., eculizumab) can be considered in refractory cases. Supportive treatments in the intensive care unit may be necessary [81,85]. Recent systematic literature reviews and meta-analyses investigating direct oral anticoagulants have recommended against their use in these patients [86,87].

#### *4.3. Pulmonary Arterial Hypertension*

Pulmonary hypertension (PH) is classified into five major categories, according to its clinical characteristics and etiology and pulmonary arterial hypertension (PAH) associated with connective tissue diseases (CTDs) belongs to the first group and it is the second most frequent form after idiopathic PAH [88,89]. PAH is defined by the presence of an increase in mean pulmonary arterial pressure (mPAP) ≥ 25mmHg at rest (assessed by right heart catheterization (RHC)) with a normal pulmonary capillary wedge pressure (≤15 mmHg) and increased pulmonary vascular resistance (PVR) > 3 wood units (WU) [73]. Less frequently, SLE patients can present PH secondary to chronic pulmonary thromboembolism (group 4), mitral stenosis due to Libman-Sacks endocarditis (group 2), pulmonary venoocclusive disease (group 1), ILD-associated PH (group 3) [88–92].

According to the REVEAL registry (Registry to Evaluate Early and Long-term Pulmonary Arterial Hypertension disease management), SLE patients display the second highest prevalence of PAH after systemic sclerosis (SSc) [93,94]. The real prevalence of PAH among SLE patients is unknown. Past studies have reported different results due to the method used for diagnosis (right heart catheterization (RHC) versus transthoracic echocardiography (TTE)) and the cut-off value used for the diagnosis [94]. The majority of patients are women with a mean age at PAH diagnosis of about 45 years, and with its prevalence and severity increasing with time from SLE onset. PAH can occasionally be the first manifestation of SLE. Usually, PAH tends to be moderate with systolic PAP of 40–60 mmHg and PVR between 5 and 15 WU [93–95]. Some possible risk factors for PAH are Raynaud's phenomenon, active renal disease, vasculitic manifestations, pleuritis, pericardial effusion, ILD, SLEDAI ≤9, lack of rash, low erythrocyte sedimentation rate (ESR) ≤ 20 mm/h. Among immunological parameters associated with PAH: aPL, Anti-U1-RNP and anti-SSA/Ro have been described [94]. The pathogenesis of SLE-PAH is

probably multifactorial and is not completely understood. Multiple factors such as genetic predisposition, environmental stimuli and immune system dysfunction could lead to an imbalance between vasoconstrictor and vasodilator mediators resulting in an increase in PVR [94,96]. aPL, anti-endothelial cells and anti-endothelin receptor antibodies, vasculitis, vasospasm, inflammation, decreased oxygen saturation, apoptosis and smooth muscle cell proliferation contribute to the development of the typical lesions of idiopathic PAH, such as plexiform lesions, smooth muscle cell hypertrophy, intimal proliferation, and collagen deposition [94,96]. Moreover, in SLE-associated PAH, there is an involvement of pulmonary veins and perivascular inflammatory infiltration [94,96,97].

Clinical presentation is non-specific, progressive and related to right ventricle dysfunction and includes dyspnea, dry cough, fatigue, weakness, exercise intolerance, angina, syncope, and hemoptysis; hoarseness due to recurrent laryngeal nerve compression, wheeze caused by large airway compression, and exercise-induced vomiting can be present in advanced cases. Symptoms are initially exercise-related, but in advanced cases occur at rest. With progression of right ventricle failure, lower limb edema, liver enlargement, abdominal distention and ascites may develop. Exceptionally, severe dilatation of pulmonary artery may complicate with its rupture or dissection leading to a cardiac tamponade. Physical findings may include: accentuated pulmonary component of the second heart sound, left parasternal lift, right ventricle third sound, murmurs indicative of tricuspid and/or pulmonary regurgitation, wheeze, and crackles; elevated jugular pressure may be present in advanced cases [88,94]. The gold standard for the diagnosis is RHC that can show some rough etiologic characterization. TTE is a non-invasive and low-cost method for the screening and follow-up of PAH patients. Other ancillary investigations may be used, such as HRCT of the lungs for the diagnosis of ILD, ventilation/perfusion scintigraphy for the assessment of chronic thromboembolism, pulmonary function tests that may show an isolated reduction of DLCO [88,94].

Early aggressive treatment aimed at normalizing PAP can improve survival. Vasodilators (e.g prostacyclin analogues), endothelin receptor antagonists (ERAs) (e.g., bosentan), phosphodiesterase 5 inhibitors (PDE-5Is) (e.g., sildenafil), guanylate cyclase stimulants (e.g., riociguat), prostacyclin IP receptor agonist (e.g., selexipag) and calcium channel blockers (CCB) (in those with a positive response to acute vasodilator testing) have shown good results. In more severe and/or refractory forms a combination with two or more different classes of drugs can be considered [49,88,94,98–105].

Side effects are in part shared by vasodilators agents. Limiting factors for CCB dose increasing are generally lower limb peripheral oedema and systemic hypotension. In the group of ERAs, ambrisentan and bosentan are associated with abnormal liver function tests (in the 0.8–3% for the former and in the 10% for the latter) with ambrisentan also associated with peripheral oedema [88,100,103]. Macitentan is not associated with liver toxicity, but a reduction in hemoglobin levels ≤8 g/dL was observed in 4.3% of patients in the study of Pulido et al. [88,106]. PDE-5Is side effects are mainly related to vasodilation such as headache, flushing and epistaxis and are mild to moderate [88]. The most frequent adverse events with riociguat were hypotension, dizziness, peripheral oedema, vomiting and anemia [105]. With beraprost the most adverse events (common with other prostanoids) are headache, flushing, jaw pain and diarrhea [88], while epoprostenol also carries the risk of a long-term intravenous catheter [88,102,104]. According to the GRIPHON study, most frequent adverse events with the use of selexipag are similar with therapies that target the prostacycline pathway (e.g., headache, diarrhea, nausea, dizziness) and are more frequent during the titration period [98].

Some studies have reported a beneficial effect of immunosuppressive therapy in SLEassociated PAH. Among immunosuppressants, CYC +/− glucocorticoids showed good response; other small studies evaluated RTX, MMF and cyclosporine. Immunosuppressants can be combined with vasoactive agents in more severe forms. Supportive treatments such as diuretics, anticoagulants and oxygen may be beneficial [88,94,107–110].

PAH affects quality of life and survival of SLE patients. Data from REVEAL registry reveal that CTD-associated PAH has a worse prognosis compared to idiopathic PAH; however, among CTDs-associated PAH, SLE patients seem to have a better prognosis, with a 1-year survival rate of 94% vs. 82% of SSc [93,94,111]. Cardiac failure and arrhythmias are the most frequent causes of death in patients with SLE-PAH [9,94].

#### **5. Pleural Disease**

Pleuritis is the most frequent lung manifestation in patients with SLE, occurring, often in association with pericarditis, in about 40–60% of patients during the course of the disease, although in autoptic studies up to 83% of patients can show signs of pleural involvement [10,112]. Of note, it is the only SLE manifestation of the respiratory system included in the diagnostic criteria [5]. Pleuritis, with or without pleural effusion, can be the first manifestation of SLE in the 3% and 1% of SLE patients, respectively [113,114]. Pleural involvement can be present also in overlap syndromes like rhupus syndrome [115]. The clinical picture can vary from asymptomatic, incidental findings on imaging, to pleuritic chest pain that is increased with deep inspiration, dyspnea, dry cough, fever and other systemic manifestations. Pleural effusion can be uni- or bilateral, usually mild to moderate, rarely massive. Occasionally pleuritis can be dry [10,49]. Pathogenesis of pleural effusion is thought to be due to ICs deposition on pleural surfaces. Histopathologic studies have shown the presence of a non-specific lymphoplasmacytic infiltration with rare evidence of IC-mediated vasculitis [115]. Pleuritic fluid is sterile, exudative, and yellow-tinged, but occasionally it can be turbidous or seroematic. It contains inflammatory cells such as neutrophils, but it can show a predominance of mononuclear lymphocytic cells, especially in longstanding cases. It also contains glucose levels similar to those of plasma (60– 95 mg/dL), increased levels of adenosine deaminase, decreased levels of complement and ANA, in particular with titer ≥ 1:160. It has a greater pH (>7.35) and lower lactate dehydrogenase (LDH) levels (<500 IU/L or <2 times upper limit of normal for serum) than in patients with RA or tuberculosis. LE cells can be seen showing a low sensibility (about 40%) and a specificity of 80%. However, none of these characteristics are specific to SLE pleuritis [10,49,113,115–117]. Differential diagnosis may be difficult, since SLE patients can have pleural effusions for many reasons including infections, renal and cardiac failure, pulmonary embolism, and rarely malignancies. It is interesting to note that in SLE pleuritis CRP can be elevated also in the absence of infections [116]. Pleural biopsy can occasionally be necessary, only to rule out tuberculosis or malignancy [116]. Prognosis is usually favorable, with a good and rapid response to CS at medium dosage, although development of progressive pleural fibrosis leading to fibrothorax has been described. Nonsteroidal anti-inflammatory drugs (NSAIDs) can be used for milder cases and spontaneous resolution can also occur. In more severe cases CS can be used (in patients already on steroid therapy an increase of dosages may be needed). In chronic forms, hydroxychloroquine can be used as a glucocorticoid-sparing agent. Major immunosuppressants (e.g., CYC and azathioprine) are not used, unless in the case of a concomitant systemic involvement. An association of IVIg and cyclosporine has been used in chronic, refractory pleural effusion. Chest drainage, pleurodesis and/or pleurectomy are rarely necessary in severe refractory cases [51,113,117–119].

#### **6. Infections**

SLE patients are at high risk of severe infections, by either common or opportunistic pathogens, the majority of which are lung infections, but also urinary tract, soft tissue and skin. Bacteria are the most commonly implicated agents, followed by viruses and fungi [120]. In the EuroLupus cohort, 36% of patients developed an infection and about 30% of deaths were related to infections in the five-year follow-up [121]. In addition, SLE patients have a higher incidence of respiratory failure and a high mortality rate for the ones admitted to the intensive care unit (ICU) with pneumonia as the most common cause of death. It is estimated that up to half of SLE patients develop major infections during the course of the disease [121–123].

Different causes accounting for this increased risk have been postulated. A genetic, non-Mendelian predisposition has been hypothesized, since the risk for severe infections seems to be increased prior to the development of SLE and a great number of genetic polymorphisms have been studied. Immunologic dysfunctions can involve both adaptive and innate immunity, in particular: complement deficiency, Ig deficiency, functional asplenia, altered cytokine production, impaired chemotaxis and phagocytosis are the major alterations thought to be involved [97,120–124]. SLE patients can present underlying structural alterations in the respiratory tract, such as respiratory muscle weakness, parenchymal disease, bronchiectasis, atelectasis with impaired local mucociliary clearance and defense against infections [97,120–124].

Immunosuppressants are well known risk factors for infections, both traditional (e.g., CYC, azathioprine) and new biologic agents (e.g., RTX and belimumab). CS are an oftenunderestimated cause of immunosuppression, especially when used in long term courses (>3 weeks), at relatively high dosage and in association with other immunosuppresants. On the contrary, antimalarials seem to have a protective role against infections both by allowing the reduction of CS dosage and by exerting a direct antimicrobial activity. It is also interesting to note that the risk of infections parallels disease activity [120].

Many pathogens can cause infections in SLE patients: Streptococcus pneumoniae is the most frequent cause of respiratory tract infections. Along with Salmonella, it is also associated with bacteriemia in the context of functional asplenia. Among fungal pathogens, Pneumocystis jiroveci, Criptococcus neoformans, Candida albicans, Aspergillus have been identified in SLE patients. Viral infections have been reported in particular with cytomegalovirus and varicella zoster virus, often in the context of a disseminated infection. SLE patients are also at increased risk for tuberculosis and infections with non-tuberculous mycobacteria [120–126]. Protozoa infections, also with rare pathogens such as Lophomonas blattarum, have been reported [127].

Diagnostic workup for infections in SLE patients may be challenging; infections can have an atypical course due to immunosuppression, moreover lung infections can simulate a lupus flare. In this context, infections must be always ruled out in a SLE patient with lung complaints and/or the appearance of a new infiltrate prior to increase the immunosuppressive therapy. Bronchoscopy with BALF analysis may be very useful for the isolation of pathogens and start of a targeted therapy [120,122]. A reduction of the immunosuppressive therapy for a short period may be necessary in severe cases during antimicrobial therapy in order to improve the immune response.

Prevention of infections can be adopted with seasonal influenza and pneumococcal vaccination and with Pneumocystis jirovecii prophylaxis in at risk patients [128–130].

#### **7. Miscellanea**

#### *Shrinking Lung Syndrome*

Shrinking lung syndrome (SLS) is a rare manifestation of SLE affecting less than 1% of SLE patients [131], with about 100 cases described to date [132]. Older papers reported a higher prevalence of 18–27%, while a prevalence of up to 7% has been described among patients with refractory SLE [132–134]. It was described for the first time in 1965 by Hoffbrand and Beck [135], and subsequently it has occasionally been described in other autoimmune diseases (e.g., systemic sclerosis, primary Sjögren's syndrome, RA and undifferentiated arthritis) [136,137]. It is characterized by progressive exertional dyspnea, pleuritic chest pain and, less frequently, cough. It can be observed in every phase of the disease but usually it occurs in long standing disease, often as the only main organ involvement of SLE, with women more often affected than men. There is no correlation with SLE activity. Physical findings are often normal, sometimes bibasilar rales can be heard. Chest X-rays show reduced lung volumes, elevated hemidiaphragms (also monolateral) and less commonly basilar atelectasis due to poor chest expansion, pleural effusions and pleural thickening. CT scan is usually negative for parenchymal disease. Ultrasound and fluoroscopy have been proposed to study diaphragm mobility. PFTs show a restrictive pattern (reduced forced expiratory volume in the 1st second, forced vital capacity and total lung capacity) with a deterioration compared to previous tests, while carbon monoxide transfer corrected for lung volume (KCO) is normal. Echocardiography does not show any signs of PAH. No specific association was found between serologic markers and the disease, it was suggested an association with Anti-Ro/SSA. Since there are no specific diagnostic criteria, the diagnosis is one of exclusion [131,132,138–141]. The pathogenesis of this condition is not known, and several mechanisms have been proposed in recent years: micro-atelectasis with surfactant deficiency, phrenic nerve neuropathy, primary respiratory muscle myopathy, diaphragmatic fibrosis, steroid induced myopathy, pleural adhesions, and pleuritic chest pain with reduced chest expansion by an inhibitory reflex [135,140,142–145].

The majority of patients received high dose of CS, even with iv pulses, with improvement occurring in several weeks, but in some cases even in 48 h [140,141]; anecdotal data support the use of immunosuppressive agents such CYC, azathioprine, methotrexate, MMF after CS failure or as CS-sparing agents [132,139,141]. RTX has been shown to improve lung function and pain in some cases [146]. Choudhury et al. reported improvement of one patient treated with belimumab [132]. Theophylline has shown to improve diaphragmatic strength and improve PFT [147], beta-agonists could reduce diaphragmatic fatigue thanks to their positive inotropic effect [148], theophylline and beta agonists may be more efficacious if combined with CS [141]. An improvement in PFT after hematopoietic stem cells transplantation has also been described [149]. Physiotherapy could be useful to improve lung volumes and prevent impaired chest wall expansion, but it could be limited by pain [141]. Antalgic agents may be considered in the initial phase [140], while in severe respiratory weakness ICU admission and mechanical ventilation may be required [141]. Prognosis seems favorable, with a rapid improvement of symptoms, and progressive improvement, stabilization or only minor deterioration of PFTs, although full recovery is rare. Pain can persist for a long time, despite improvement in PFT. Death, due to respiratory failure is unusual [133,140,141]. In this regard, an early diagnosis and an appropriate treatment is mandatory.

#### **8. Conclusions**

SLE can affect any part of the respiratory tract, with various degrees of severity and at any phase of the disease course. Respiratory manifestations may display acute and/or chronic course and since most respiratory signs and symptoms are non-specific, differential diagnosis is often challenging. However, the early recognition and management of SLErelated respiratory manifestations is essential to prevent complications and the worsening of disease prognosis.

**Author Contributions:** Writing—Original Draft Preparation, S.D.B.; Writing—Review & Editing A.A.; Writing—Review & Editing F.C. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Data Availability Statement:** No new data were created or analyzed in this study. Data sharing is not applicable to this article.

**Conflicts of Interest:** The authors declare no conflict of interest.

#### **References**


### *Review* **Pharmacological Interventions for Pulmonary Involvement in Rheumatic Diseases**

**Eun Ha Kang <sup>1</sup> and Yeong Wook Song 2,\***


**Abstract:** Among the diverse forms of lung involvement, interstitial lung disease (ILD) and pulmonary arterial hypertension (PAH) are two important conditions in patients with rheumatic diseases that are associated with significant morbidity and mortality. The management of ILD and PAH is challenging because the current treatment often provides only limited patient survival benefits. Such challenges derive from their common pathogenic mechanisms, where not only the inflammatory processes of immune cells but also the fibrotic and proliferative processes of nonimmune cells play critical roles in disease progression, making immunosuppressive therapy less effective. Recently, updated treatment strategies adopting targeted agents have been introduced with promising results in clinical trials for ILD ad PAH. This review discusses the epidemiologic features of ILD and PAH among patients with rheumatic diseases (rheumatoid arthritis, myositis, and systemic sclerosis) and the state-of-the-art treatment options, focusing on targeted agents including biologics, antifibrotic agents, and vasodilatory drugs.

**Keywords:** rheumatic; interstitial lung disease; pulmonary arterial hypertension; targeted therapy
