Long-term Outcomes of Periurethral Sphincter Botulinum Toxin in Female Chronic Urinary Retention

Purpose: Nonneurogenic chronic urinary retention is an uncommon problem in young female individuals, and a well characterised causes is Fowler syndrome (primary disorder of urethral sphincter relaxation). Intermittent catheterisation is often challenging, and gold standard treatment sacral neuromodulation is not widely available. Urethral sphincter botulinum toxin injection has been shown to be effective cross-sectionally, however little is known about long-term outcomes. Methods: Female individuals presenting with urinary retention due to Fowler syndrome were reviewed retrospectively from a single tertiary referral centre over an 11-year period (2010-2021). One hundred units of onabotulinum toxin A (BoTX-A) was injected into the striated urethral sphincter in a divided dose by the periurethral approach. Efficacy and side effects were assessed 4 weeks after injection. Results: Thirty-three female individuals with a mean age of 40.1 +/- 14.1 years received 165 unique urethral sphincter BoTX-A injections over 11 years. Nineteen individuals (57.6%) presented in acute urinary retention, and 28 (84.8%) were reliant on catheterisation. Twenty-one individuals (64%) responded to BoTX-A injections and had a significantly raised baseline maximum urethral closure pressure (MUCP), compared to nonresponders (114.6 cm H2O, P= 0.012). Side effects were reported following 19 injections (11.5%) however, were mild and transient. Fifteen individuals received more than 1 botulinum toxin injection (median, 3 injections), with a median interval of 112 days (interquartile range) and efficacy persisted following repeat injections and no safety concerns were seen. Conclusions: Sphincter botulinum toxin through the periurethral approach is safe and effective following repeat injections, and offers a low-cost, minimally invasive alternative to managing female chronic urinary retention due to Fowler syndrome, particularly when there was a high baseline MUCP.