What causes stress incontinence: Fallacies, fascias and facts

Abstract

The traditional view of the pathophysiology of stress urinary incontinence (SUI) was that a loss of urethral support was the primary abnormality present. Recent research has challenged this hypothesis, demonstrating that impaired urethral function plays the key causative role. Improving our understanding of the underlying pathologic mechanisms is important to identifying the cause of treatment failures and for developing novel therapies to treat SUI. O ver the last century, several hypotheses have been proposed to explain the pathophysiology of stress urinary incontinence (SUI). These theories have largely been based on uncontrolled clinical observations or comparing women with stress incontinence to women undergoing urodynamics that did not have stress incontinence (i.e., urge incontinence), focusing on loss of urethral support and an open vesical neck as the primary causative abnormalities. This traditional view of SUI causation has, however, been challenged by recent research investigating the potential role of urethral function in SUI using asymptomatic volunteers for comparison. ROSE studyThe Research On Stress incontinence Etiology (ROSE) study compared measurements of urethral support and function in women with primary SUI to asymptomatic volunteers. 1 This was a casecontrol study involving 103 women with SUI and 108 asymptomatic controls matched for age, race, parity and hysterectomy. The key variables analyzed were maximum urethral closure pressure (MUCP), urethral and pelvic organ support, levator ani muscle function, and intravesical pressure.The study showed that the mean MUCP was 42% lower among women with primary SUI (40.8 cm H 2 O vs. 70.2 cm H 2 O; Fig. 1). MUCP was found to be, by far, the strongest predictor of SUI; the effect size (1.47) was substantially higher than that of any other single predictor. In fact, after adjusting for body mass index (BMI), MUCP alone correctly classified 50% of cases. No measure of urethral support had an effect size greater than 0.6. Ultrasound investigationThe investigators of the ROSE study were surprised by their findings that MUCP was the most powerful predictor, with an effect size so much greater than any of the urethral mobility variables assessed in the study. To alleviate concerns that they had not included the correct urethral mobility parameter in their assessments, they subsequently performed a secondary analysis of ultrasound videos of the ROSE subjects' urethral mobility during coughing. 2 This was carried out by a panel of international experts who were asked to identify which patterns they felt were most likely to be associated with stress incontinence.The investigators were surprised to discover that none of the experts were able to consistently discern which women were stress incontinent and which were continent based on review of the ultrasounds alone. Indeed, the mean accuracy of these evaluators was 57.4% (i.e., only 7% better than the success rate one would expect by random chance). This finding further supports the concept that ure...