What is intrinsic sphincter deficiency?

• A. Inadequate urethral closure due to weak or absent sphincter function, leading to leakage with minimal stress.
• B. Overactivity of the detrusor muscle causing strong contractions.
• C. Urinary obstruction causing retention.
• D. Increased bladder capacity.

Answer: (A)

Intrinsic sphincter deficiency refers to a failure of the urethral sphincter itself to maintain closure. In this problem, the key idea is that the sphincter mechanism is weak or absent, so the urethra cannot stay closed even with only small increases in abdominal pressure. The intrinsic sphincter (the part of the sphincter not dependent on support structures) normally maintains a baseline closure pressure and augments closure during stress. When its function is impaired, the urethral closure pressure drops below the pressure exerted on the bladder, leading to leakage with minimal or even no provocation.

This is distinct from situations where leakage occurs because of poor urethral support (hypermobility) while the sphincter itself may still close adequately, or from other types of incontinence like detrusor overactivity, which presents with urge-related leakage due to involuntary bladder contractions. Intrinsic sphincter deficiency is often associated with conditions that damage the sphincter mechanism or its innervation, such as aging, prior pelvic surgery, radiation, or neuropathy, and on testing may show a low maximum urethral closure pressure.