Influence of sacral neuromodulation on electrosensation of the lower urinary tract

We prospectively investigated whether neuromodulation of the S3 root influences the sensory threshold to electrical stimulation in the lower urinary tract.

The study included 7 women and 3 men receiving S3 neuromodulation at 210 msec. and 25 Hz. with the Interstim PNE system for a mean of 5 days. Neuromodulation was done unilaterally in 6 cases and bilaterally in 4. The sensory threshold was determined by electrodes placed randomly against the mucosa of the empty bladder on the left and right sides, in the urethra in women, and in the prostatic and penile urethra in men. Thresholds were measured at each location with neuromodulation on and off.

With bilateral neuromodulation on all 4 patients had a lower bladder threshold than with neuromodulation off. In unilateral neuromodulation the threshold was significantly lower during neurostimulation on the ipsilateral side. There was no effect on the threshold on the arm or in the urethra. The effect was noted in patients in whom neuromodulation was and was not clinically successful.

Neuromodulation on S3 influences the nervous system involved in electrosensation of the bladder but not the skin afferent innervation or the nerves involved in urethral electrosensation. These data support the hypothesis that S3 neurostimulation is effective mainly through the afferent nervous system in the pelvic nerves.