Sacral neuromodulation effects on periurethral sensation and urethral sphincter activity.

AIMS To characterize the effect of sacral neuromodulation (SNM) on urethral neuromuscular function. METHODS Following IRB approval, women with refractory overactive bladder (OAB) underwent standardized urethral testing prior to and after Stage 1 SNM implantation. Periurethral sensation was measured using current perception thresholds (CPT). Striated urethral sphincter activity was quantified using concentric needle electromyography (CNE) and Multi-Motor Unit Action Potential (MUP) analysis software. Nonparametric analyses were used to characterize pre/post changes with intervention. Baseline CPT and CNE findings were compared between SNM responders and non-responders. RESULTS Twenty-seven women were enrolled in this pilot study with a mean age of 61 ± 13 years. Twenty of 26 women (76.9%) responded to SNM and went to Stage 2 permanent implantation. Four (14.8%) withdrew after Stage 1 implantation; three of the four withdrawals had not had therapeutic responses to SNM. CPT and CNE parameters did not significantly differ from baseline 2 weeks after SNM. Pre-SNM urethral sensation was not significantly different between responders and non-responders. However, responders had larger amplitude, longer duration and more turns and phases at baseline approaching significance, reflecting more successful urethral reinnervation, than non-responders. CONCLUSIONS SNM does not alter urethral neuromuscular function 2 weeks post Stage 1 implantation.