The Efficacy of Intradetrusor Onabotulinumtoxin A Injection for Refractory Overactive Bladder Syndrome—A Single-Center Prospective Study

<b>Background/Objectives:</b> Intradetrusor botulinum toxin injection is a well-established third-line therapy for patients with refractory overactive bladder (OAB) and detrusor overactivity (DO). Botulinum toxin type A (BoNT-A) is most commonly used due to its prolonged therapeutic duration. We aimed to evaluate the effectiveness of intradetrusor BoNT-A injection therapy in managing refractory OAB by performing a urodynamic study (UDS). <b>Methods</b>: The patients were prospectively enrolled between February 2020 and March 2021. The patients received treatment regimens comprising behavioral modification therapy, pelvic floor muscle physiotherapy, and/or OAB medications for at least three months. The UDS procedure was carried out by a single examiner, in accordance with the International Continence Society standards for good urodynamic practice. A total of 100 units of BoNT-A was dissolved in 10 mL of saline, and 0.5 mL (5 units) was injected at 20 sites on the posterior wall of the bladder. The primary endpoint was the change in DO, which was measured using the UDS from the baseline to two months after treatment with BoNT-A. <b>Results</b>: Prior to treatment initiation, DO was observed in all the patients during the UDS. The occurrence of DO during the filling phase demonstrated a significant decrease following treatment, with DO no longer identified in 27.3% of the patients. The first sensation of bladder filling, maximum cystometric capacity, DO, and terminal DO all demonstrated significant improvement after intradetrusor BoNT-A injection, based on the UDS. The OAB symptom scores also significantly decreased after BoNT-A therapy. <b>Conclusions</b>: The present study demonstrated that intradetrusor BoNT-A injection significantly improved symptoms in patients with OAB who had been unresponsive to various treatments. This study also demonstrated the usefulness of performing a UDS before and after treatment to prove the efficacy of BoNT-A.