Assessment of the Excitability of Spinal Motoneurons Using Stimulus-response Curves of the Bulbocavernosus Reflex

Overview

Spasticity is commonly observed in neurological conditions such as Multiple Sclerosis and spinal cord injury. "Peripheral" spasticity, concerning in particular the striated muscles of the limbs is nowadays well known and studied with clinical scales (Ashworth, Taridieu...) or even electrophysiological methods (H-reflex, T-reflex...). However, this spasticity can also affect the perineal muscles and more generally the pelvic muscles. However, there is to date no validated and standardized method for evaluating this pelvi-perineal spasticity. The aim of the study will be to assess the spinal motoneurons excitability by using the stimulus-response curves of the bulbocavernosus reflex.

Spasticity defined by Lance in 1980 is "a motor disorder characterized by a velocity dependent increase in the tonic stretch reflexes (muscle tone) with exaggerated tendon jerks, resulting from hyperexcitability of the stretch reflexes as one component of the upper motor neuron syndrome". The occurrence of spasticity, which is common in neurology when the pyramidal tract is affected, is commonly observed in the "peripheral" striated muscles. However, spasticity also concerns the perineal musculature, with "the exaggeration of the stretching reflex of the muscles accessible to pelvic touches". Although there are measurement scales commonly used in clinical practice, such as the Ashworth and Tardieu scales, or electrophysiological instrumental techniques (H reflex , T reflex), there is actually no objective and standardized measurement technique for pelvic spasticity. An interesting tool could be the bulbocavernosus reflex (BCR) which is a polysynaptic reflex with sacral integration. In addition to its diagnostic and topographical value due to its sacral integration, BCR could testify, by its modulation, to the control of the alpha motor neuron pool. It could therefore allow to assess motoneuronal excitability, whose increase may lead in central patients with supra-connal lesions (spinal cord injuries (SCI), multiple sclerosis (MS)), to a release of sacral automatism with exacerbation of reflex responses whether bladder (detrusor overactivity), sphincter (detrusor-sphincter dysynergia) or rectal (rectal overactivity). The aim of the study will be to assess the sacral spinal motor neuron excitability using the stimulus-response curves of the BCR. The investigators will conduct a prospective monocentric observational study in a specialized neuro-urology department. The main objective of this study will be to evaluate the spinal motoneuron excitability according to the degree of bladder repletion by modelling recruitment slopes (stimulus-response curves) of the BCR. First of all, the investigators will assess the feasibility of conducting an analysis of BCR stimulus-response curves during a perineal electrophysiological exploration performed in a diagnostic context in patients referred for urinary, anorectal or genito-sexual disorders. BCR will be recorded after electrical stimulation of the dorsal nerve of the penis or the dorsal nerve of the clitoris, using a concentric needle electrode inserted into the left and then right bulbcavernous muscle. Stimulations will be performed at progressively increasing intensities and each response will be recorded. Acquisition will be performed using a Dantec™ Keypoint® G4 EMG device, Natus®. The initial stimulation intensity will be at the motor threshold, i.e. the degree of stimulation that determines a stable latent motor response and will then be increased by 10 to 10 mA to obtain the following 4 reflex responses. Once the acquisition will be completed, the curves will be analyzed allowing the analysis of the area under the curve (AUC) and the construction of the stimulus-response curves. In a second step, the investigators will evaluate the possibility of modelling these stimulus-response curves after EMG recording using pre-gelled disposable surface electrodes placed on the external anal sphincter (EAS) during a cystometry performed in patients consulting for urinary disorders. The stimulation technique will be identical as described previously. Finally, the modulation of spinal motoneurons excitability according to the degree of bladder filling will be assessed by modelling the BCR stimulus-response curves, before and during a cystometry.