Abstract: PD54-01
Sources of Funding: Medtronic Unrestricted Research Grant

Introduction

Sacral nerve stimulation(SNS) is used for refractory overactive bladder(OAB). Its mechanism of action is unknown, but likely involves spinal reflexes and afferent signaling to the brain. This study used functional magnetic resonance imaging(fMRI) to measure real-time SNS effects on brain activity in OAB.

Methods

Following IRB approval, women with non-neurogenic refractory OAB who responded to SNS via InterStim II device, had a stable program for 3 or more months, and received no adjuvant OAB treatment were recruited. Enrolled patients completed pre-fMRI validated symptom and quality of life instruments[UDI-6, IIQ-7, PGI-S, Perceived Urgency Intensity(PUI)]. Stimulus settings were recorded, devices switched off for a 5-day washout, and instruments repeated. Three fMRI scans below, at, and above stimulus sensory threshold were done. Images were 2-dimensional gradient echo-planar imaging blood oxygenation level dependent contrast(EPI-BOLD) acquired over 5 stimulator-off and 4 on cycles of 42 seconds each. Output images use single voxel p-value 0.05 with false positive error of 0.05 (cluster-analysis determined).

Results

A total 13 patients were enrolled (3 did not undergo fMRI, 4 were excluded for poor OAB symptom control or low image quality), 6 completed fMRI. The sample had a median age 52[36-64] years. Urinary bother significantly worsened with 'washout' while symptoms worsened with a trend toward significance. Voiding diary data supported this. _x000D_ An overall pattern of brain activation generally progressed with increasing stimulation, but activation of the right inferior frontal gyrus remained stable, while deactivation of the pons and periacqueductal gray matter was only noted with sub-sensory stimulation. Sensory stimulation activated the insula but deactivated the medial and superior parietal lobes. Suprasensory stimulation activated multiple structures and the expected S3 sensory region. All devices had normal impedances after fMRI and PUI(p0.36) nor PGI-S(p0.36) changed from baseline.

Conclusions

Varying SNS stimulus influences fMRI signal intensity. These results suggest sacral nerve stimulation may have a centrally-mediated mechanism of action.

Funding

Medtronic Unrestricted Research Grant