Brain excitability changes in the relapsing and remitting phases of multiple sclerosis: A study with transcranial magnetic stimulation

Objective: Recent functional and imaging studies have substantially contributed to extend the concept of multiple sclerosis (MS), classically regarded as a disease limited to the myelin axonal sheath. Several findings, in fact, point to a parallel involvement of neuronal components of the central nervous system (CNS) in the course of MS. In the present study, therefore, we explored, in MS patients, some characteristics of central motor pathways related to changes of neuronal excitability as measured using transcranial magnetic stimulation (TMS). Methods: Seventy-nine patients affected by relapsing-remitting (RR) MS were examined using single and paired TMS in order to assess excitability changes in the hand motor cortex occurring during relapse and/or remission of the disease. The analyzed parameters were: motor-evoked potential (MEP) threshold, silent period (SP), intracortical inhibition (ICI) with paired pulses from 1 to 6 ms interstimulus intervals (ISIs), and central motor conduction time (CMCT). Results: The analysis of variance exhibited a strong correlation (P