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

Abstract

Background: In patients with Multiple Sclerosis (MS), transcranial magnetic stimulation (TMS) has shown signifi cant prolongation of central motor conduction time (CMCT). Abnormal CMCT may refl ect 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 defi nite 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 fi gure of eight coil. Parameters determined included: motor threshold, central motor conduction time (CMCT), latencies and amplitude of MEP at 120% of motor threshold. Results: Modifi cations 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.

Keywords

• multiple sclerosis
• magnetic stimulation
• motor evoked potentials