Onabotulinum Toxin A Is a Viable Intervention for Bladder Neck Obstruction in Women: A Prospective Pilot Study of Patient Reported Outcomes.

[INTRODUCTION] Primary bladder neck obstruction (BNO) occurs when the bladder neck fails to open during voiding. The cause of BNO is not fully understood but may be related to smooth muscle hypertrophy, increased collagen deposition, or sympathetically mediated high-tone smooth muscle of the urethra. As there is symptom overlap with other urinary pathology, diagnosis is challenging, and there are limited treatments with a paucity of data. Onabotulinum toxin A (BoNT-A) to the bladder neck has shown improvement in symptoms caused by BNO in women in a small retrospective study. We aimed to prospectively analyze the therapeutic efficacy of BoNT-A to the bladder neck as a treatment option for women with BNO.

[MATERIALS AND METHODS] We performed a pilot study recruiting female patients with pelvic pain and BNO from September 2023 to July 2024. Patients were diagnosed with BNO using the urodynamic Nitti Criteria, patient symptoms of hesitancy, straining, and/or dysuria, and cystoscopic evidence suggesting BNO. Patients were assessed prior to BoNT-A injection to the bladder neck and 4-6 weeks post-procedure. The procedure consisted of 100 units of BoNT-A reconstituted to 2 mL of Marcaine or saline with 0.5 mL injected cystoscopically at 10, 2, 5, and 7 o'clock in the bladder neck. The primary outcome was the change in the Female Genitourinary Pain Index Scale (Female GUPI, scores range from 0 to 44, lower scores are better). Secondary outcomes pre-procedure versus post-procedure included the Pelvic Floor Distress Index-20 (PFDI-20, scores range from 0 to 300, lower scores are better), a pain visual analogue scale (VAS, ranging from 0-no pain to 10-worst pain), and post-void residual (PVR) volumes. The Global Response Assessment (GRA, -3 to +3, +3 better) was included post-procedure. Data were analyzed using descriptive statistics, and outcomes were compared using the Wilcoxon signed-rank test.

[RESULTS] Twenty-two female patients with BNO were recruited to our study. Patients had significant improvement in the Female GUPI with a decrease in scores from a median of 34.5 (IQR 31-36) pre-bladder neck BoNT-A to 26 (20.3-29.8) post-procedure (p = 0.002). The Pain, Urination, and Quality of Life subscales of the Female GUPI all demonstrated significant improvement (all p < 0.05). Median improvement on the GRA was 1.4 (SD 1.4). Compared to baseline, there was improvement in the Urinary Distress Index-6 (UDI-6) subscale (p = 0.012) but not in overall PFDI-20 total scores, which includes prolapse and bowel symptoms in addition to the UDI-6 (p = 0.161). The median PVR prior to treatment was 126 mL (IQR 50-193), and after treatment decreased to 28 (14-59) (p = < 0.001).

[CONCLUSIONS] BNO in women encounters limited therapeutic options. BoNT-A to the bladder neck may be considered. BoNT-A to the bladder neck demonstrated improvement in pain, lower urinary tract symptoms (LUTS), and PVR volumes in those with refractory BNO.