motor evoked potentials modification in different forms and stages of multiple sclerosis

Background: In patients with Multiple Sclerosis (MS), transcranial magnetic stimulation (TMS) has shown significant prolongation of central motor conduction time (CMCT). Abnormal CMCT may reflect sub-clinical involvement of motor pathways and correlate with clinical motor disability.The present study was undertaken to determine the diagnostic yield of TMS in MS, to assess the strength of the correlation between clinical disability and motor evoked potentials (MEP) abnormalities in different stages of progression of MS and to evaluate the possibility that TMS may be used to monitor clinical evolution in MS over time. Materials and methods: Fifty nine patients with clinically definite multiple sclerosis and eighteen healthy volunteers were included in the study. Patients were divided in three subgroups according to the moment and the character of disease. Transcranial magnetic stimulation (TMS) parameters were evaluated using single pulse TMS and a figure of eight coil. Parameters determined included: motor threshold, central motor conduction time (CMCT), latencies and amplitude of MEP at 120% of motor threshold. Results: Modifications of at least one parameter were observed at 91% cases. We noticed an increase of motor threshold, CMCT, cortical latencies and decrease of motor evoked potential (MEP) amplitude at 120% of motor threshold. Conclusion: There are significant correlations observed between the abnormalities in CMCT and the degree of motor disability. The changes of MEP parameters were more pronounced in secondary-progressive MS. TMS is a highly sensitive technique to evaluate cortico-spinal conduction abnormalities in MS, in monitoring motor disability and the course of the disease.