Botulinum toxin A used for urinary incontinence is administered by injection into which structure?

• A. Detrusor muscle
• B. External urethral sphincter
• C. Trigon of bladder
• D. Ureteral orifice

Answer: (A)

Botulinum toxin A treats overactive bladder by directly dampening the bladder’s smooth muscle activity. Injecting into the detrusor muscle delivers the toxin right where involuntary contractions originate, and it blocks acetylcholine release from the nerve endings to detrusor fibers. This reduces involuntary contractions during filling, increases bladder capacity, and lowers urgency and leakage.

Injecting into the external urethral sphincter would lower sphincter tone, which could worsen leakage or cause retention rather than improve incontinence. Targeting the trigone or ureteral orifice isn’t the typical approach for detrusor overactivity and wouldn’t directly address the main source of urge contractions. Therefore, the detrusor muscle is the appropriate structure for this treatment.