Spatial Integration of Somatosensory Inputs during Sensory-Motor Plasticity Phenomena Is Normal in Focal Hand Dystonia.

C Terranova,G Chillemi,R Maggio,A Quartarone,F Morgante,A Calamuneri,V Rizzo,P Girlanda

doi:10.1155/2018/4135708

Abstract

Background Surround inhibition is a system that sharpens sensation by creating an inhibitory zone around the central core of activation. In the motor system, this mechanism probably contributes to the selection of voluntary movements, and it seems to be lost in dystonia. Objectives. To explore if sensory information is abnormally processed and integrated in focal hand dystonia (FHD) and if surround inhibition phenomena are operating during sensory-motor plasticity and somatosensory integration in normal humans and in patients with FHD. Methods. We looked at the MEP facilitation obtained after 5 Hz repetitive paired associative stimulation of median (PAS M), ulnar (PAS U), and median + ulnar nerve (PAS MU) stimulation in 8 normal subjects and 8 FHD. We evaluated the ratio MU/(M + U) ∗ 100 and the spatial and temporal somatosensory integration recording the somatosensory evoked potentials (SEPs) evoked by a dual nerve input. Results FHD had two main abnormalities: first, the amount of facilitation was larger than normal subjects; second, the spatial specificity was lost. The MU/(M + U) ∗ 100 ratio was similar in healthy subjects and in FHD patients, and the somatosensory integration was normal in this subset of patients. Conclusions. The inhibitory integration of somatosensory inputs and the somatosensory inhibition are normal in patients with focal dystonia as well as lateral surrounding inhibition phenomena during sensory-motor plasticity in FHD.

Highlights

Dystonia is a motor disorder characterized by sustained involuntary muscular contractions resulting from cocontraction of antagonistic muscles and overflow into extraneous muscles [1]
Figure 1: 5 Hz rPAS induced an increase in motor evoked potentials (MEPs) size recorded from abductor pollicis brevis (APB) muscle in both patients and controls; repeated measure analysis of variance (ANOVA) showed a significant effect of time [F = 88 38; P < 0 001], but the amount of facilitation was different between the two groups, as shown by the time × group interaction [F = 21 14; P < 0 001]
Figure 2: 5 Hz rPAS induced an increase in MEP size recorded from abductor digiti minimi (ADM) muscle in both patients and controls; repeated measure ANOVA showed a significant effect of time [F = 89 22; P < 0 001] and time × group interaction [F = 29 73; P < 0 001]

Summary

Introduction

Dystonia is a motor disorder characterized by sustained involuntary muscular contractions resulting from cocontraction of antagonistic muscles and overflow into extraneous muscles [1]. Focal hand dystonia frequently develops after repetitive movements in the presence of overtraining These clinical observations have pointed out toward the presence of subtle abnormalities of plasticity, within somatosensory system, which may predispose individual to dystonia after excessive training [2]. Proprioceptive inputs coming from adjacent body parts are abnormally integrated in dystonia This aberrant spatial gating, probably caused by an altered lateral surrounding inhibition, could contribute to the motor impairment present in dystonia [5]. To explore if sensory information is abnormally processed and integrated in focal hand dystonia (FHD) and if surround inhibition phenomena are operating during sensory-motor plasticity and somatosensory integration in normal humans and in patients with FHD.

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Conclusion