The Change of Silent Periods Following Transcranial Magnetic Stimulation in Storke Patients

J Korean Assoc EMG Electrodiagn Med 2002;4(2):73-78.
Published online May 10, 2002.

Abstract

Objective: Transcranial magnetic stimulation of the motor cortex during tonic muscle contraction produces a motor evoked potential followed by a silent period (SP) in the electromyogram. The SP reflects the cortical inhibition of the motor pathway. We sought to characterize the SPs in stroke patients and to determine the relationship between the SPs and several clinical findings such as muscle power, the duration of illness and site of lesion. Method: Subjects were 43 stroke patients who were radiologically proved to have unilateral brain lesion and whose muscle power of abductor pollicis brevis (APB) was greater than fair grade. Stimulation thresholds when SPs first appeared and SPs induced by 30% increased stimulation above the threshold were measured from the APB muscles of both affected and unaffected limbs. Results: SPs were significantly longer in the affected limbs than in the unaffected limbs. There was no significant interside difference (ISD) in the stimulation threshold. We could demonstrate a negative correlation between the muscle power and ISD of the SPs. There was no significant correlation between ISD and duration of illness, pyramidal tract and cortical involvement. Conclusion: The SP prolongation is correlated to the decreased muscle strength in stroke patients. The SP study probably contributes to a better quantification of the central motor function in stroke patients.

Key Words: Transcranial magnetic stimulation, Silent period, Stimulation threshold, Interside difference, Stroke