**3. Results**

#### *3.1. Subject Characteristics in ME/CFS and Non/ME/CFS Patients*

Overall, there were 55 patients diagnosed with ME/CFS—with or without comorbidities. As regards results in these two groups, most of the respondents (58%) had been having fatigue for the last year or last two years (29%), whereas the minority—for the last six months (10%). In comparison, patients not diagnosed with ME/CFS reported having fatigue for the last year (60%) or the last six months (40%).

Asked about the onset of fatigue, most patients in the ME/CFS groups considered that emotional (24%) or physical (22%) stress is a contributing factor, whereas 16% reported that it developed gradually with a progression of an underlying chronic disease and 15%— because of sleep disturbances. In the group without ME/CFS on the other hand, most of the patients (60%) reported that they could not remember or identify the onset or the reason for fatigue and none reported that it begun together with a progression of a chronic disease. Emotional stress (30%) was considered a cause for fatigue in more cases than physical stress (15%) in the non-ME/CFS group.

Most patients in both groups with ME/CFS (65%), as well as patients in the non-ME/CFS (50%) group stated that fatigue is constant and invariable throughout the day, whereas for 16% of respondents in both of the ME/CFS groups, compared to none in the non-ME/CFS group fatigue was more severe in the mornings.

Regarding the core symptoms, apart from fatigue with PEM (100%), myalgia (96%), headache (87%), arthralgia (86%) and difficulty concentrating (84%) are the five most common ones in the two groups with ME/CFS, whereas in the non-ME/CFS group those are: headache (91%), myalgia (73%), difficulty concentrating (64%), neck stiffness (64%) and fatigue (55%). All of the symptoms are listed in the Table 1. A graphical representation of the differences regarding symptoms is shown in the Figure 1. It shows that fatigue, myalgia, arthralgia and sleep disturbances are the main symptoms, which have a tendency to differ in ME/CFS patients compared to non-ME/CFS patients.

**Table 1.** Clinical signs of ME/CFS, ME/CFS with comorbidities and non-ME/CFS patients.


In most cases (93%) our respondents in both of the ME/CFS groups could not identify any first-degree relatives having similar symptoms of fatigue, but if such a tendency was reported (7%), then in all of the cases the relative was mother.

Considering the effect fatigue has on the employment status, almost all respondents (82%) in both—the ME/CFS and ME/CFS with comorbidities groups had reduced their workload or become unemployed.

Regarding comorbidities presenting together with ME/CFS, the overall prevalence was 66%. Fibromyalgia, chronic hepatitis and Lyme disease occurred in 20%, 9% and 5%, respectively. EBV, enterovirus infection each occurred in 5% of cases, whereas lymphadenopathy and anaemia were registered in 4% of cases. The schematic representation of all diagnosis can be assessed in the Figure 2, where comparison of two diagnostic groups can be seen—the group with ME/CFS (*n* = 19) and the one with ME/CFS and at least one comorbidity (*n* = 36). It must be noted that all infectious or inflammatory diseases were not in their acute phase at the time of the research.

Comparing self-reported treatment methods to decrease the symptoms of fatigue, in the non-ME/CFS group almost none of the respondents (90%) had found any solutions to decrease fatigue, whereas in both groups with ME/CFS 38% reported using help-self strategies, including physical activities, sleep hygiene, physiotherapy and walking, 38% had not found any solutions and 24% reported using pharmacological drugs, the most commonly used being non-steroidal anti-inflammatory drugs (90%).

The VAS score was also calculated for each individual and the average result was seven in both—the ME/CFS and ME/CFS with comorbidities group compared to six in the non-ME/CFS group.

**Figure 2.** Representation of the proportion of ME/CFS (*n* = 19) and ME/CFS + comorbidities (*n* = 36)

#### Chronic*3.2. Characteristic Differences in the Three, Previously Defined Groups*

 obstructive pulmonary disease.

 COPD:

in the study population;

As shown in the Figure 3 there is a mild but significant increase of the overall scores of the pattern of fatigue, showing the lowest mean score in the patient group with non-ME/CFS diagnosis in comparison to ME/CFS (Figure 3a), however the level of the highest individual scores was established among those patients with ME/CFS with at least one comorbidity, indicating that comorbidities might be associated with a more severe course of the disease (Figure 3b).

**Figure 3.** The overall scores of characteristics of fatigue expressed in %: (**a**)—in non-ME/CFS and all ME/CFS patients; (**b**)—in non-ME/CFS, ME/CFS and ME/CFS with at least one comorbidity patients. \*—significance level *p* < 0.05 (**a**)—Unpaired *t*-test, (**b**)—Brown-Forsythe and Welch ANOVA tests with Dunnett's T3 multiple comparison test as post-hoc procedure.

Comparing the correlation coefficients in all three groups (Figure 4), those respondents in the non-ME/CFS group, who tend to identify more causes for fatigue and whose duration of fatigue was longer show an increased number of current symptoms (r = 0.59, r = 0.30, respectively). Additionally, more symptoms were identified in older patients (r = 0.30) and females (r = −0.48). In the ME/CFS group without comorbidities, on the other hand, more symptoms were identified in younger patients (r = −0.43) and in those who tend to mention less possible causes for their fatigue (r = −0.30). In both—non-ME/CFS and ME/CFS group without comorbidities more consequences of fatigue were identified by men than women (r = 30, r = 32, respectively).

**Figure 4.** Presented correlograms showing the covariance of the studied variables in all three diagnostic groups—non-ME/CFS, ME/CFS and ME/CFS+comorbidities. The values in the squares represent Spearman's rank correlation coefficients, showing the strength and direction of associations and the more pronounced ones are indicated by coloured circles (red—negative association, green—positive).

Regarding VAS, there was a tendency for the VAS to be higher in younger patients (r = −0.55) and a negative correlation was found regarding an increase in VAS and the duration of fatigue in the ME/CFS group without comorbidities (r = −0.31). No correlations regarding VAS and previously mentioned parameters were found in the other two groups.

Only one correlation was found between the ME/CFS and the comorbidity group, showing that there is a tendency for the duration of fatigue to increase as the age increases (r = 0.40), as well as with an increasing age people tend to identify more possible causes for their fatigue (r = 0.32).

As to the correlation analysis in all of the groups together, only one correlation was identified, showing a tendency for the age to increase in the first (non-ME/CFS), the second (ME/CFS) and the third (ME/CFS + comorbidities) groups, respectively (r = 0.34).
