P69-S Cutaneous silent period behavior in different motor neuron diseases phenotypes

Abstract

Background The cutaneous silent period (CSP) corresponds to a reduced electric activity of a contracting muscle, after electrical stimulation of sensory fibers. The afferent volley causes a presynaptic inhibition of spinal motor neurons (LMN) modulated by complex spinal circuits. CSP behavior in different motor neuron diseases (MND) phenotypes is unknown. Materials and methods We included 20 MND patients and 15 controls. CSP was obtained by applying electrical stimulation of the 5th finger. Surface EMG recordings were obtained from ADM muscle. CSP duration was defined by the time between a drop of rectified averaged EMG below 80%, and the final return above 80%, of baseline EMG. The mean duration was obtained from 10 consecutive curves obtained before and during co-contraction of the contralateral ADM muscle. Results MND patients had a median age of 59 years. 12 were diagnosed as amyotrophic lateral sclerosis (ALS), 6 as progressive muscular atrophy (PMA), 2 as primary lateral sclerosis (PLS). Median CSP duration was similar between controls and patients. During contralateral ADM contraction, CSP duration did not change in controls, patients with ALS and PMA, but decreased by 28% in PLS patients. Conclusions We present preliminary results suggesting that CSP behavior is not homogenous in different phenotypes of MND. We previously observed that reflex contralateral activation of the homonymous contralateral hand muscles is frequent in patients with PLS, indicating spinal cord hyperexcitability. Our CSP results suggest that this method can contribute to dissect the mechanisms underlying abnormal LMN excitability in patients with corticospinal tract lesion.