There are over 30 studies of PTNS in the published literature; the earliest are case series or single arm efficacy studies [
3,
7••,
23], three are randomized, controlled trials (RCT) [
2,
5••,
6••], and two are long-term follow-up studies of patients who were responders in the OrBIT and SUmiT Trials [
4••,
26••]. Over half of the patients receiving PTNS therapy in the SUmiT trial, a randomized, double-blinded, sham controlled study, reported moderate or marked improvement in bladder symptoms (54.5 % PTNS patients vs. 20.9 % sham, p < 0.001) [
5••]. In addition, PTNS reduced the number of voids per day from 12.3 at baseline to 9.8 at 12 weeks, a mean reduction of -2.4 vs. a reduction of -1.5 in the sham group (p < 0.001). Urge incontinence episodes per day decreased from 3/day at baseline to 0.3/day at 12 weeks vs. 1.8/day at baseline to 1.0/day for sham (p < 0.001) [
5••]. In a randomized, controlled study, Finazzi-Agro et al. report that PTNS significantly increased voided volume compared to sham treatment (150 mL to 186 mL in the PTNS treatment group vs. 146 mL to 150 mL in the sham group, p <0.001) [
2]. In a urodynamic study, Klingler et al. report that PTNS increased mean total bladder capacity from 197 mL at baseline (range 35–349) to 252 ml (range 78–384 mL, p < 0.01) after 12 weeks of therapy [
22]. When PTNS was compared against tolterodine extended release in the OrBIT study, both therapies demonstrated statistically significant improvements in incontinence episodes, voids per day, and nocturia [
6••]. Although the gains in voided volume appear to be equivalently modest for both PTNS and for antimuscarinics, these gains are associated with significant improvements in subjective measures (see below), underscoring that these changes are clinically meaningful. The demonstrated increase in voided volume potentially represents an additional hour of bladder capacity.