Cortical involvement in myopathies: Insights from transcranial magnetic stimulation.

Objective: There is increasing evidence that an involvement of central nervous system (CNS) can occur in several myopathies. Transcranial magnetic stimulation (TMS) may represent a valuable tool for investigating important neurophysiological and pathophysiological aspects of cortical involvement in neuromuscular disorders. In this review paper we aimed to perform a systematic search of the studies employing TMS techniques in subjects suffering from myopathies.
Methods: A literature search was conducted using PubMed and Embase. We identified and reviewed 9 articles matching the inclusion criteria. One hundred twenty patients were included in these studies, which have applied TMS in patients with muscle disorders.
Results: To date, a few studies using TMS have been performed in myopathic patients and detected subclinical abnormalities in cortical reactivity and plasticity. The most consistent finding was a decrease in intracortical inhibition, which likely represents a non-specific compensatory mechanism of the CNS in an attempt to overcome the muscle deficit through an increase of the motor cortex output to deficient muscles.
Conclusions: Application of TMS to characterize the pathophysiology of the CNS in these subjects appears to be safe and may lead to the development of valuable biomarkers. Well-defined motor cortical excitability patterns can be identified in the different muscle diseases, even if preliminary findings should be confirmed in future studies in larger cohorts of patients.
Significance: TMS studies may shed new light on the physiological and pathophysiological mechanisms underlying the cortical involvement in muscle disorders.
(Copyright © 2017 International Federation of Clinical Neurophysiology. Published by Elsevier B.V. All rights reserved.)