CORTICAL SILENT PERIOD EVOKED BY TRANSCRANIAL MAGNETIC STIMULATION INISCHEMIC STROKE

Objectives: Transcranial magnetic stimulation (TMS) of the motor corte x produces motor evoked potentials (MEPs). Besides this excitatory res ponse, TMS has inhibitory effects. When TMS is performed during volunt ary muscle contraction, the MEP is followed by a pause in electromyogr aphic activity (cortical silent period, SP). The aim of this study was to evaluate the clincial usefulness of the SP. Methods: We studied SP changes in 50 patients with acute hemispheric brain infarction. A sti mulator with a round coil and a fixed intensity of 90% of maximum was used to evoke MEPs. Results: SP was elicited on the affected side in 2 9 of the 50 patients. The mean SP duration was markedly longer on the affected side in the patient group. There were no significant differen ces between left and right sides in the means of the MEP amplitude rat io (amplitude related to corresponding amplitudes to peripheral electr ic stimulation) and MEP latencies in the patient group. Prolonged SP w as found in 25 of the 29 patients (86%) whereas only 4 (14%) had abnor malities in MEP latency or amplitude ratio. The mean SP duration was s ignificantly prolonged also in a subgroup of 14 patients with normal h and function. Conclusions: The SP measurement is an easily performed a nd sensitive method to detect even subclinical disturbances in motor s ystem function in ischemic stroke. (C) 1998 Elsevier Science Ireland L td. All rights reserved.