Predictors of success for first stage neuromodulation: Motor versus sensory response

Purpose: We investigated whether intraoperative motor or sensory response is more predictive of successful sacral neuromodulation using the InterStim (R) system. Materials and Methods: A total of 35 patients with medically refractory frequency, urgency and urge incontinence were enrolled in the study. All patients underwent lead placement for quadripolar test stimulation under local anesthesia with intravenous sedation. Confirmation of correct lead placement was by observation of known motor and sensory responses that result from third sacral nerve stimulation. Motor and sensory responses were documented intraoperatively. Patients had a 1-week trial of stimulation, and those who had greater than 50% improvement in symptoms had placement of the implantable pulse generator. Those without at least 50% improvement in their symptoms had the quadripolar lead removed. Results: Of the 35 patients enrolled 21 had successful quadripolar test stimulation and went on to permanent implantable pulse generator placement. Of the patients who had successful quadripolar test stimulation 95% demonstrated positive intraoperative motor response whereas only 21.4% of patients with unsuccessful quadripolar test stimulation demonstrated positive motor response. If only a positive sensory response was elicited, patients had only a 4.7% chance of having a positive quadripolar test stimulation. Conclusions: A positive quadripolar test stimulation (greater than 50% improvement in symptoms) with InterStim (R) sacral neuromodulation is more likely when intraoperative lead placement results in positive motor response vs only sensory response.