Which statement best describes the pathophysiology of stress urinary incontinence?

• A. Leakage occurs due to detrusor overactivity.
• B. Leakage occurs due to motor neuron disease.
• C. Leakage occurs due to urethral hypermobility or intrinsic sphincter deficiency when intra-abdominal pressure rises.
• D. Leakage occurs due to high bladder capacity.

Answer: (C)

Stress incontinence leaks happen when the urethral closure mechanism can’t keep urine in during moments that raise abdominal pressure, like coughing or lifting. The usual culprits are urethral hypermobility, where the pelvic floor doesn’t support the urethra well, and intrinsic sphincter deficiency, where the sphincter itself isn’t able to maintain a tight seal. When intra-abdominal pressure rises, the bladder neck and urethra are pushed downward; if the closure pressure from the sphincter and pelvic support isn’t enough, urine leaks despite the bladder not contracting. This is different from urge incontinence, which stems from detrusor overactivity, causing leakage with little or no pressure rise. High bladder capacity isn’t the mechanism here. So the best description is leakage due to urethral hypermobility or intrinsic sphincter deficiency when intra-abdominal pressure increases.