1. Introduction
Urinary incontinence is an involuntary leakage of urine that can cause symptoms in a wide range of severity and affect the patient’s quality of life. Symptoms could force major changes in the way the patient lives their life, including changes in the patient’s physical and mental health. The cost to treat urinary incontinence, either medically or surgically, is well over
$10 billion per year [
1].
The International Association of Urinary Control defined involuntary urinary leakage, in the presence of both urgent and increased abdominal pressure, as mixed urinary incontinence (MUI) [
2].
Among women with urinary incontinence, approximately one-third have mixed incontinence, that is, an issue across all age groups with symptoms of both stress and urgency incontinence [
3].
Stress incontinence is the involuntary loss of urine following increased intra-abdominal pressure or physical exertion (coughing, sneezing, jumping, lifting, exercising, etc.). Pseudo urgency syndrome is a specific type of MUI. It refers to a MUI with stress urinary incontinence (SUI) as the main pathological feature but presents as urge urinary incontinence (UUI) within a normal cystometrogram. Urge incontinence is the involuntary loss of urine preceded by a sudden and severe desire to pass urine. Bladder contractions may be stimulated by a change in body position (from supine to upright) or with sensory stimulation. The pathophysiology of urge incontinence is uninhibited bladder contractions caused by irritation or the loss in neurologic control of bladder contractions.
MUI may be urge predominant, stress predominant, or equal. The pathophysiology and treatment of MUI has lacked attention and in-depth research, especially in regard to treatment strategy. Urinary incontinence, particularly the mixed type, is an issue across all age groups. The purpose of this study, therefore, is to explore the causes of UUI symptoms in MUI patients and to analyze the treatment methods of MUI.
4. Discussion
Urinary incontinence is a kind of disease that can seriously trouble the daily life of many women. The most common forms of urinary incontinence are SUI and UUI. Among them, SUI patients often have UUI symptoms, which is to say MUI. Compared with simple SUI, the mixed urgent symptoms of MUI have a more serious impact on the psychological distress and daily life of patients [
6]. However, there are still many disputes about the etiology and treatment strategy of MUI.
The prevalence of MUI ranges from 0.6% to 59.2% [
7], while in SUI cases, the incidence rate of UUI symptoms can be as high as 69.3% [
8]. In this group of cases, 40 patients were clinically diagnosed with MUI, accounting for 57.1% of all patients with SUI symptoms. If MUI was diagnosed only by urodynamic bladder compliance, low volume, and uninhibited contraction then the proportion was only 17.1%. It can now be seen that there is a great difference between the subjective symptom diagnosis of patients and the prevalence of MUI as diagnosed by urodynamics. Some studies believe that this difference is caused by different research objects, or differences in patient statements, diagnostic standards, or even other factors [
9]. However, the high prevalence of UUI caused by this difference is obviously unconvincing.
In this study, after urodynamic examination of 40 enrolled MUI patients, only 12 patients had MUI urodynamic changes such as unstable bladder contraction. The urodynamics of the remaining 28 patients showed negative signs of MUI, which indicated that most of the MUI patients diagnosed by symptoms had normal bladder compliance, suggesting that they may have urgent symptoms caused by mental factors of the patients that could be caused by SUI. Digesu et al. [
10] performed urodynamic analysis on 1626 patients with UUI and SUI. These patients had symptoms such as frequent urination and urgency of urination; it was found, however, that only 18% of the patients’ urodynamic test results suggested the presence of UUI, which could be diagnosed as MUI. Lin et al. [
11] performed urodynamic examination on 340 patients with lower urinary tract symptoms and found that only one patient could be diagnosed as possessing MUI. These results are consistent with our study. The reason for these type of results may be related to the lower degree of UUI in MUI patients, or in the symptoms of urgency of urination that originate from the urethra, which cannot be detected by urodynamic examination [
12]. However, this latter inference does not seem to fully explain this phenomenon.
In this study, we found that the patients whose clinical symptoms were MUI but whose urodynamic examination was otherwise normal—all had psychological and behavioral UUI symptoms of the fear of urination overflow. That is to say, in order to avoid leakage of urine, SUI patients urinate immediately when they have the intention to urinate for the first time. Thus, this formed a habit of repeated urination, resulting in enhanced self-urination awareness, therefore forming a “pseudo” UUI, following their normal urodynamic examination. In addition, the patient also retrained their bladder due to the fear of repeated urination from urinary incontinence, which further aggravated the symptoms of frequent urination and urgency. Osman et al. [
13] named this symptom of frequent urination and the subsequent urgency to avoid inducing SUI as “pseudo urgency syndrome”. To sum up, we can conclude that the actual proportion of MUI patients who, in reality, have the pathological basis of UUI is low, because of the interference of patients with “pseudo urgency syndrome”. There are great differences in the epidemiological investigation of MUI in different regions, resulting in a higher proportion of MUI patients in SUI. The real cause of MUI is mental UUI caused by SUI.
As the mechanism of simple SUI is mainly stress bladder dysfunction, the most common causes are vaginal delivery and age, which lead to a weak pelvic floor support structure, lax bladder neck closure when abdominal pressure increases, and shorter functional urethra—thus SUI occurs. The pathological basis of UUI is high bladder excitability or detrusor overactivity and poor compliance [
14]. Therefore, it is difficult to explain these with the same pathogenic factor or mechanism, which will inevitably lead to disputes over treatment methods.
Restoring the original anatomical structure of the pelvic floor through surgery is the main method to treat SUI at present, and its short-term cure rate can reach more than 90% [
15]. However, it is still controversial whether MUI patients should undergo surgical treatment first. The 2017 edition of urinary incontinence guidelines in China [
16] advised that patients with MUI should be treated with caution. In particular, those with MUI who are dominated by UUI should be treated with drugs in a conservative manner first, and those who fail to respond to conservative treatment should then be treated with surgery. This is because it has been reported that 40% of patients with MUI will continue to have frequent urination and urgent urination after surgery [
17]. However, recent studies have found that the urinary incontinence symptoms of MUI patients can be greatly improved after surgical treatment, and there is no obvious tendency of deterioration. Natale et al. [
18] treated 86 patients with urinary incontinence with TOT. After an average follow-up of 59 months, they found that the cure rates of SUI and MUI patients could reach 83.7% and 74.4%, respectively. Padmanabhan et al. [
19] treated 487 MUI patients with TOT, and the subjective improvement rate of patients reached 72.8%. A medium and long-term study by Zhang et al. [
12] found that the cure rate of UUI could also reach 76.92% if only TOT was given to MUI patients, and the curative effect remained stable for a long time. The quality-of-life of patients was significantly improved. A 5-year follow-up study by Yonguc et al. [
20] also showed that the effective rate of TOT in treating MUI patients was 83.3%.
In this study, the effective rate of SUI symptom treatment in MUI patients after surgical treatment was similar to that in simple SUI patients, i.e., as high as 85%. It should be noted that 28 patients with urodynamic “Negative” signs of MUI showed significant improvement in UUI symptoms after treatment and did not require long-term drug intervention. Therefore, for patients with “pseudo urgency syndrome”, the real cause is SUI. When SUI is cured, UUI symptoms will naturally be alleviated. Patients with non-inhibitory contractions in other urodynamic examinations can also obtain long-term satisfactory effects through pelvic floor rehabilitation training and drug treatment. Therefore, for MUI patients, surgery should be performed first in order to solve SUI symptoms, so that patients can eliminate the psychological worries of fear of urine leakage. Thus, patients dare to hold their urine, reducing the training stimulation of repeated urination, and improving or even eliminating UUI symptoms.