Urethral Sphincter Nerve
and Muscle Damage: What You Should Know

Intrinsic sphincter deficiency is a condition in which the urethral sphincter is unable to close enough to retain urine in the bladder. The anatomic support of the urethra may be normal.

Intrinsic sphincter deficiency (ISD) is due to reduced blood or nerve supply bladder neck and proximal urethra. The urethral sphincter may become weak after pelvic surgery (eg, failed bladder suspension surgery and hysterectomy) because of nearby nerve damage or excessive scarring of the urethra and surrounding tissues. Childbirth can cause damage to any of these structures. Additional causes of urethral dysfunction include pelvic radiation or neurologic injury.

Women with severe intrinsic sphincter deficiency do not always have the usual urethral excessive movement during the bearing-down process. The urethra remains open at rest. Whenever intra-abdominal pressure exceeds urethral pressure, involuntary urine loss ensues. Because the urethra cannot remain closed, the patient experiences almost continuous urinary loss.

Estrogen influences the function of the female urethra. The lack of estrogen at menopause leads to thinning of the vaginal and urethral tissue with reduced blood supply. Lack of estrogen is a risk factor for developing intrinsic sphincter deficiency, but estrogen replacement may reverse its effects.