Cortical silent period in patients with amyotrophic lateral sclerosis

Transcranial magnetic stimulation (TMS) during a muscle contraction induces a motor-evoked potential (MEP) in the skeletal muscle followed by a cessat ion of EMG activity, the cortical silent period (C-SP). The C-SP is a usefu l parameter to indicate the activation of the motor system. Accurate determ ination of the C-SP can be important in amyotrophic lateral sclerosis (ALS) , a progressive disorder of unknown etiology characterised by degeneration of upper and lower motor neurons. The aim of this study was to evaluate the sensitivity of C-SP as an index of motor system involvement, in ten patien ts affected by ALS, with a mean duration of the disease: 5.5+/-3.4 months, by means of an objective computer-aided method to measure C-SP and its rela tionship to stimulation intensity. C-SP duration was significantly reduced in ALS patients compared to controls at low stimulation intensity correspon ding to an MEP threshold increased by 15%. While in less severely affected patients C-SP duration approached control values at higher stimulation inte nsities (25 and 50% upper MEP threshold), in more severe ALS subjects it sh owed a further reduction, allowing them to be discriminated. (C) 1999 Elsev ier Science B.V. All rights reserved.