Cortical silent period evoked by transcranial magnetic stimulation in ischemic stroke

Transcranial magnetic stimulation (TMS) of the motor cortex produces motor evoked potentials (MEPs). Besides this excitatory response, TMS has inhibitory effects. When TMS is performed during voluntary muscle contraction, the MEP is followed by a pause in electromyographic activity (cortical silent period, SP). The aim of this study was to evaluate the clinical usefulness of the SP.

We studied SP changes in 50 patients with acute hemispheric brain infarction. A stimulator with a round coil and a fixed intensity of 90% of maximum was used to evoke MEPs.

SP was elicited on the affected side in 29 of the 50 patients. The mean SP duration was markedly longer on the affected side in the patient group. There were no significant differences between left and right sides in the means of the MEP amplitude ratio (amplitude related to corresponding amplitudes to peripheral electric stimulation) and MEP latencies in the patient group. Prolonged SP was found in 25 of the 29 patients (86%) whereas only 4 (14%) had abnormalities in MEP latency or amplitude ratio. The mean SP duration was significantly prolonged also in a subgroup of 14 patients with normal hand function.

The SP measurement is an easily performed and sensitive method to detect even subclinical disturbances in motor system function in ischemic stroke.