Is a 50% improvement threshold adequate to justify progression from sacral neuromodulation testing to implant?

A ≥50% subjective improvement in urinary symptoms during sacral neuromodulation testing (SNM-I) is currently used as the indication for progression to second-stage implantation (SNM-II). While most patients will have successful SNM-I and proceed to SNM-II, deterioration in efficacy over time has been reported. It remains unclear if the durability of efficacy is related to the initial symptom reduction. We sought to determine if the degree of improvement after SNM-I is sufficient to predict long-term success.

The records of all patients who underwent sacral neuromodulation (SNM) for overactive bladder were reviewed. Subjects were divided into those who reported 50%-75% improvement (Group 1) and more than 75% improvement (Group 2) after SNM-I. Differences in clinical variables and long-term device efficacy were compared between groups.

Of 213 patients who underwent SNM-I, 137 underwent permanent device implantation. A total of 76 (55%) and 61 (45%) patients reported 50%-75% (Group 1) and more than 75% (Group 2) symptomatic improvement, respectively. With a mean follow-up of 46 months, 44% of Group 1 patients and 68% of Group 2 patients still had a functioning device providing the symptomatic benefit (p = 0.007). Univariate analyses identified the presence of stress urinary incontinence at baseline and having a more than 75% improvement after SNM-I as predictors of long-term functional success.

Compared to patients reporting 50%-75% symptomatic reduction after SNM-I, individuals with a more than 75% improvement during SNM-I were more likely to maintain device efficacy over time. Additional study is warranted to determine if the improvement threshold for progression to SNM-II should be increased.