Patterns of tined lead migration in sacral nerve modulation

A Prospective Feasibility Study to Differentiate Sacral Neuromodulation Lead Electrode Configurations Using Motor and Sensory Thresholds and Locations of Sensation

Background Accurate positioning and effective programming of sacral neuromodulation (SNM) relies upon the use of several acute stimulation measurements. While the clinical utility of these acute measurements including pelvic floor motor thresholds (PFMT), toe/leg motor thresholds (TMT), and sensory thresholds (ST), are widely accepted, their usefulness in quantitative research remains unclear. The purpose of this prospective study was to test these measurements and gauge their utility in future research. Methods Eight participants received Axonics SNM, 6 Medtronic Interstim II, and 2 Medtronic Micro SNM. PFMT was measured after implantation. ST and the location of sensation (LOS) were measured immediately postoperatively (PO), at pre-release from the surgery center (PR), and during a follow-up clinic visit (FU). Thresholds were compared across contact and time using linear mixed-effects models. Results Significant differences in PFMT were found across electrode configurations, with stimulation through proximal contacts exhibiting lower PFMT than distal configurations. ST displayed no significant differences across electrodes and showed minimal changes over time. LOS exhibited substantial variability across patients and periods. Conclusions Results suggest that PFMT were able to differentiate differences across electrode configurations that may be useful for future quantitative research. The lack of differences in ST and LOS across electrode configurations was interesting given the focus on these measurements clinically. Future testing is to confirm these limitations.

Functional mapping of the lower urinary tract by epidural electrical stimulation of the spinal cord in decerebrated cat model

Several neurologic diseases including spinal cord injury, Parkinson's disease or multiple sclerosis are accompanied by disturbances of the lower urinary tract functions. Clinical data indicates that chronic spinal cord stimulation can improve not only motor function but also ability to store urine and control micturition. Decoding the spinal mechanisms that regulate the functioning of detrusor (Detr) and external urethral sphincter (EUS) muscles is essential for effective neuromodulation therapy in patients with disturbances of micturition. In the present work we performed a mapping of Detr and EUS activity by applying epidural electrical stimulation (EES) at different levels of the spinal cord in decerebrated cat model. The study was performed in 5 adult male cats, evoked potentials were generated by EES aiming to recruit various spinal pathways responsible for LUT and hindlimbs control. Recruitment of Detr occurred mainly with stimulation of the lower thoracic and upper lumbar spinal cord (T13-L1 spinal segments). Responses in the EUS, in general, occurred with stimulation of all the studied sites of the spinal cord, however, a pronounced specificity was noted for the lower lumbar/upper sacral sections (L7-S1 spinal segments). These features were confirmed by comparing the normalized values of the slope angles used to approximate the recruitment curve data by the linear regression method. Thus, these findings are in accordance with our previous data obtained in rats and could be used for development of novel site-specific neuromodulation therapeutic approaches.

Electrophysiological Responses in the Human S3 Nerve During Sacral Neuromodulation for Fecal Incontinence

Intra-operative electrode placement for sacral neuromodulation (SNM) relies on visual observation of motor contractions alone, lacking complete information on neural activation from stimulation. This study aimed to determine whether electrophysiological responses can be recorded directly from the S3 sacral nerve during therapeutic SNM in patients with fecal incontinence, and to characterize such responses in order to better understand the mechanism of action (MOA) and whether stimulation is subject to changes in posture. Eleven patients undergoing SNM were prospectively recruited. A bespoke stimulating and recording system was connected (both intraoperatively and postoperatively) to externalized SNM leads, and electrophysiological responses to monopolar current sweeps on each electrode were recorded and analyzed. The nature and thresholds of muscle contractions (intraoperatively) and patient-reported stimulation perception were recorded. We identified both neural responses (evoked compound action potentials) as well as myoelectric responses (far-field potentials from muscle activation). We identified large myelinated fibers (conduction velocity: 36–60 m/s) in 5/11 patients, correlating with patient-reported stimulation perception, and smaller myelinated fibers (conduction velocity <15 m/s) in 4/11 patients (not associated with any sensation). Myoelectric responses (observed in 7/11 patients) were attributed to pelvic floor and/or anal sphincter contraction. Responses varied with changes in posture. We present the first direct electrophysiological responses recorded from the S3 nerve during ongoing SNM in humans, showing both neural and myoelectric responses. These recordings highlight heterogeneity of neural and myoelectric responses (relevant to understanding MOA of SNM) and confirm that electrode lead position can change with posture.