When using sacral neuromodulation (SNM) for overactive bladder (OAB), an at least 50% improvement in urinary symptoms is needed to justify progressing from the 1st stage/test phase (St1) to implantation of the device in the 2nd stage (St2). We sought to determine if this 50% improvement threshold is adequate for longer term efficacy of the device by comparing patients with a 50-75% symptom improvement after St1 who had a subsequent St2 implant to those with a >75% improvement after St1.

We conducted a retrospective review of 213 patients who underwent SNM for OAB by two surgeons from 2005 – 2018. Patients were divided into cohorts (50-75% and >75% improvement) based on symptom improvement using a combination of patient-reported degree of improvement (0-100%), symptom questionnaires, bladder diary and pad usage. Patient demographic and clinical variables were compared between the cohorts using chi-squared and t-test analyses. Cox proportional hazard regression was performed to assess for associations between these variables, reported improvement after St1, and long-term success after St2

Of 213 OAB patients who underwent St1i, 84 (39.4%) reported 50-75% improvement and 75 (90.4%) of those progressed to St2i (group 1) whereas 69 patients (32.3%) reported >75% and 60 (86.9%) of those progressed to St2i (group 2). Baseline characteristics (comorbidities, symptom scores, bladder diaries, pad usage and urodynamic parameters) were not significantly different between groups except that neuropathy was more prevalent in group 1 (29% vs 13%, p=0.01). After SNSt, improvements in symptom scores and diary/pad usage were not significantly different between groups apart from a greater improvement in AUASS bother score in group 2 (3.43 vs. 1.6, p=0.04). After St2, group 2 patients were more likely to report a >75% improvement (71.2% vs 34.2%, p<0.01). With a mean follow-up of 46 months, 24/75 group 1 patients and 31/60 group 2 patients still had a functioning device providing symptomatic benefit (p=0.06) with no significant difference found between groups on regression (OR=0.481,95% CI: 0.217 – 1.063, p=0.07).

We found no significant differences in the majority of baseline characteristics and clinical data between patients who had a 50-75% improvement and those with >75% improvement after SNM. As well, there was no statistically significant difference between groups with respect to patients with longer term device efficacy. This suggests the current threshold of an at least 50% improvement during SNM testing is adequate to progress to implantation of the device. However, the lack of a statistically significant difference between groups might be a reflection of the patient numbers and therefore these results should be interpreted with caution. It is noteworthy that the degree of bother was lower after SNM testing and the subjective degree of improvement significantly greater after stage 2 implant in the group who had >75% improvement after SNM testing. Additional study and followup is warranted to more reliably determine if we need to modify the threshold for a successful SNM test.

Based on the lack of a statistically significant difference between groups, a >50% symptom improvement threshold during SNM testing for progression to stage 2 implant seems reasonable. However, better long-term results might be achievable with a higher threshold.