Elsevier

European Urology

Volume 41, Issue 5, May 2002, Pages 562-567
European Urology

Alterations of Cortical Electrical Activity in Patients with Sacral Neuromodulator

https://doi.org/10.1016/S0302-2838(02)00029-5Get rights and content

Abstract

Objectives: Sacral neuromodulation represents chronic stimulation of the sacral (S3) nerve. So far, the mode of action and neuro-anatomical basis is unclear. Sacral reflex mechanisms as well as pontine or cortical centers of modulation have been postulated. Our aim was to evaluate possible alterations in electroencephalogram (EEG) activity as an indicator of a supraspinally mediated mechanism of sacral neuromodulation.

Materials and Methods: We analyzed serial EEGs (apparatus: Kölner Vitaport System) using electrodes placed at Fz, Cz, Cz′ and Pz in 10 patients. Subsequently, the sacral (S3) nerve was stimulated by means of an impulse generator (Medtronic, Interstim 3023) using an on-off paradigm with a 1.5 s “on” interval followed by a 10 s stimulation break. Raw data were analyzed using both Matlab 4.0 software and a specially developed averaging routine.

Results: All patients demonstrated a cortical potential complex following sacral root stimulation with an early electronegative component at 50 ms with a mean amplitude of 23 μV followed by a late potential component with a mean latency of 253 ms and a mean amplitude of 5 μV, both with a maximum at Cz, corresponding to the post-central gyrus. This finding occurred irrespective of patient’s reports of actually feeling the neuromodulator being switched on and off.

Conclusion: In neuromodulation responders, both short and long latency cortical potentials can be reproduced with a maximum at the sensory cortical area. Although these potentials are similar to cognitively mediated “event-related potentials”, they are clearly distinct from any subjective sensory or even painful response since several patients of this series have not been able to feel any neuromodulator action. Therefore, this pilot study indicates a supraspinally mediated site of modulation, most probably in sensory cortex areas.

Introduction

Sacral neuromodulation can be a beneficial treatment option in patients suffering from therapy-resistant detrusor instability or detrusor hypocontractility [1], [2], [3], [4], [5]. The neuro-anatomical basis and the mechanism of action is unclear. A sacral reflex mechanism as well as supraspinal centres of modulation have been postulated [4], [5]. On the one hand Schmidt et al. postulate that the efficacy of neuromodulation depends on intact sacral and supraspinal reflex pathways, which was confirmed by Hohenfellner et al. who were able to show that no neuromodulation effect was seen in patients with high incomplete and complete spinal cord injuries [6], [7]. On the other hand Zvara et al. showed a restoration of bladder hyperreflexia in a rat model with complete spinal lesions [8]. Further Blok et al. were able to show that in human volunteers cortical and pontine micturition sites are strongly involved in co-ordinated micturition and that direct stimulation of the pontine micturition centre results in a relaxation of the urethral sphincter and in a contraction of the detrusor muscle [9], [10].

The aim of this pilot study was to assess possible effects of sacral (S3) nerve neuromodulation on cortical electrical activity.

Section snippets

Material and methods

We studied 10 patients who had been implanted a sacral (S3) one-channel neuromodulator after a diagnostic positive PNE-test (six men, four women). All the patients showed an improvement of 50% or more after neuromodulator implantation, which was identified urodynamically (in accordance to the multicenter study by Jonas et al. [11]). The mean age was 49 years (28–69). Four patients had been diagnosed with a neurogenic bladder dysfunction, six patients had an idiopathic bladder dysfunction (Table

Results

All patients (Table 1) displayed very similar effects on cortical electrical activity after neurostimulation of S3 root (Fig. 5). Due to technical reasons we had to consider a delay of 110 ms after pressing the “on button” for the onset of sacral root stimulation (Fig. 3, Fig. 5). A first electronegative peak, occurring with a mean latency of 50 ms and with a mean amplitude of 23 μV which can be referred to as an early sensory evoked potential comparable to pudendal evoked potentials was

Discussion

Long latency somatosensory evoked potentials (SSEPs) were described for many decades. Although the knowledge of their generators is still limited, they have been widely used, for example in the odd-ball paradigm in psychometric and dementia testing, the best known component being the P300, a positive cortically recorded potential with a mean latency of 300 ms, commonly regarded as a cognitively mediated phenomenon. On the other hand, early SSEP components like the pudendal SSEPs have become a

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