Pathophysiology of stress incontinence

Stress incontinence is a symptom - the patient's statement of involuntary loss of urine when exercising physically; a sign - the observation of involuntary loss of urine from the urethra immediately upon an increase in abdominal pressure; and a condition (Bates et al, 1977). Genuine stress incontinence (GSI) (Figure 1) occurs when the intravesical pressure, as a result of an increase in intra-abdominal pressure, exceeds the resistance by the urethral closure mechanisms, in the absence of bladder activity. Other forms of incontinence may be confused with GSI because of the similarity in symptoms and the ability to elicit the clinical sign of urinary loss with stress manoeuvres (coughing, straining, etc). Disorders associated with detrusor contraction (detrusor instability), elevated intravesical pressure (poor compliance), or increased residual urine (overflow incontinence), may have associated 'stress-induced' symptoms. Urethral instability results from the reflex relaxation of the urethra without a detrusor contraction. These disorders should not be confused with GSI which is the focus of this chapter.