Therapeutic effect of urethral sphincter onabotulinumtoxinA injection for urethral sphincter hyperactivity

Urethral sphincter hyperactivity resulting in voiding dysfunction is frequently encountered. Medical treatment might not achieve a satisfactory result. OnabotlinumtoxinA urethral sphincter injection relaxes sphincter tonicity and possibly resumes efficient voiding. This study analyzed the treatment outcomes and predictor for successful onabotulinumtoxinA treatment on these patients.

Patients with voiding dysfunction due to urethral sphincter hyperactivity and treated with injections of 100 U onabotulinumtoxinA into the urethral sphincter were retrospectively reviewed. Treatment outcomes were assessed 1 month after injection using the Global Response Assessment and were analyzed by demographic and baseline video-urodynamic characteristics.

Of the 95 patients included, satisfactory outcomes were reported in 58 (61.1%) patients. Treatment outcome was not related to age, gender, or voiding dysfunction subtype. Patients with satisfactory outcomes had a significantly smaller volume at first sensation of filling (P = 0.046), greater detrusor pressure (P = 0.027), higher maximum flow rate (P = 0.017), and smaller post-void residual (P = 0.006). In multivariate analysis, an open bladder neck during voiding was the only predictor for successful outcome (88% in satisfactory outcome, 12% in failure outcome, P < 0.001). Patients with non-neurogenic voiding dysfunction had a significantly longer therapeutic duration than those with neurogenic voiding dysfunction (9.55 ± 4.18 vs 7.44 ± 2.91 months, P = 0.033). Increased urinary incontinence was reported in 18 patients, including 6 with stress urinary incontinence and 12 with urgency urinary incontinence.

Subjective improvement was reported in 61.1% of patients with voiding dysfunction due to urethral sphincter hyperactivity after onabotulinumtoxinA urethral sphincter injection. An open bladder neck during voiding at baseline predicts a successful outcome.