Neurourology and Urodynamics 26:1020–1023 (2007) CASE REPORT Pudendal Nerve Stimulation Evokes Reflex Bladder Contractions in Persons With Chronic Spinal Cord Injury Paul B. Yoo,* Stephen M. Klein, Neil H. Grafstein, Eric E. Horvath, Cindy L. Amundsen, George D. Webster, and Warren M. Grill Departments of Biomedical Engineering, Urology, Anesthesiology and Surgery, Duke University, Durham, North Carolina Aims: Although electrical stimulation of the pudendal nerve has been shown to evoke reflex micturition-like bladder contractions in both intact and spinalized cats, there is little evidence to suggest that an analogous excitatory reflex exists in humans, particularly those with spinal cord injury (SCI). We present two cases where electrical activation of pudendal nerve afferents was used to evoke excitatory bladder responses. Subjects and Methods: A percutaneously placed catheter electrode was used to electrically stimulate the pudendal nerve trunk in two males with SCI. The response was quantified with recorded changes in detrusor pressure and EMG activity of the external anal sphincter. Results: In both individuals, frequency specific (f ¼ 20–50 Hz) activation of the pudendal nerve trunk evoked excitatory bladder contractions that also depended on the stimulus amplitude and bladder volume. Conclusion: The results suggest that selective activation of the perineal branches of the pudendal nerve may further augment the excitatory reflex evoked by electrical stimulation. Neurourol. Urodynam. 26:1020–1023, 2007. ß 2007 Wiley-Liss, Inc. Key words: electrical stimulation; spinal cord injury; percutaneous electrode; human INTRODUCTION Spinal cord injury (SCI) results in lower urinary tract dysfunction, including neurogenic detrusor overactivity and detrusor sphincter dyssynergia, that leads to inefficient voiding, recurrent urinary tract infections, and significant reduction in quality of life. 1,2 Electrical stimulation is a potential alternative to self-catheterization, and recent work has focused on evoking bladder contractions by activating pudendal nerve afferents to empty the bladder. 3 Although this reflex has been characterized in preclinical animal studies, 4–7 there are few data in humans to support the clinical trans- lation of this approach to restoring of bladder function. We investigated the presence of an analogous excitatory pudendal nerve to bladder reflex in two human volunteers with SCI. Based on stimulation parameters developed in preclinical studies, 7 a minimally invasive needle electrode was used to locate and stimulate the pudendal nerve to evoke reflex bladder contractions. METHODS Experimental protocols were approved by the Institutional Review Board of Duke University Medical Center and written informed consent was obtained from each volunteer. Subjects were prepared for urodynamic evaluation by intra-urethral insertion of a 12F catheter (Dover Rob-Nel, Kendall Healthcare, Mansfield, MA) to adjust bladder volume; a 4F PVC catheter (BPC-4L, Life-Tech, Inc., Stafford, TX) to measure vesicular pressure (P vesicle ); and rectal insertion of a 9F catheter (RPC-9, Life-Tech, Inc.) to measure abdominal pressure (P abdomen ). The bladder was filled with room temperature saline at 20 ml/min, while the anal sphincter EMG and the detrusor pressure (P detrusor ¼ P vesicle  P abdomen ) were recorded (Fig. 1A). The volume at which sustained distension-evoked bladder con- traction occurred (V th ) was used to determine subsequently the bladder volume (80% of V th ) to initiate pudendal nerve stimulation. Bladder filling was terminated under the follow- ing conditions: sustained isovolumetric bladder contractions (defined by a P detrusor above 30 cm H 2 O), fluid leak around the urethral catheter, or apparent signs of autonomic dysreflexia. The pudendal nerve was stimulated via percutaneous access. The subjects were placed in the left lateral decubitus position with their back, hips, and legs flexed. A 19 gauge insulated Tuohy needle (StimuCath, Arrow International, Reading, PA) connected to a constant current nerve stimulator (Stimuplex Dig RCB, Braun, Bethlehem, PA) was advanced perpendicular to the skin towards the nerve. The needle insertion point was 2 cm lateral and 2 cm caudal to the midpoint of a line defined between the posterior superior iliac spine and the ischical tuberosity. The proximity of the needle tip to the pudendal nerve trunk was minimized through successively finer adjustments of the stimulus amplitude (initial current ¼ 3 mA, pulse width ¼ 0.1 s and 2 Hz) and electrode tip position, until external anal sphincter twitches could be evoked with stimuli less than 1 mA. The needle was then replaced by threading a flexible 19 gauge stimulating catheter (StimuCath, Arrow International, Reading, PA) through the initially inserted electrode. Without altering the motor response, the needle was withdrawn. The catheter No conflict of interest reported by the author(s). Chris Winters led the review process. *Correspondence to: Paul B. Yoo, Department of Biomedical Engineering, Hudson Hall, Room Number 136, Duke University, P.O. Box 90281, Durham, NC 27708- 0281. E-mail: paul.yoo@duke.edu Received 29 January 2007; Accepted 12 March 2007 Published online 4 May 2007 in Wiley InterScience (www.interscience.wiley.com) DOI 10.1002/nau.20441 ß 2007 Wiley-Liss, Inc.