P268 The effects of high-dose steroids on cortical excitability in acute multiple sclerosis relapses

Abstract

Objectives Multiple sclerosis (MS) is a chronic inflammatory disease of the central nervous system which can manifest in different forms, the most common being the relapsing remitting one (RRMS). Although high dose steroids are classically used for treating MS relapses, their impact on the excitability of cortical networks was rarely addressed. Methods 21 RRMS patients completed the study. The evaluation took place before and after three day-treatment with intravenous methylprednisolone (1 g per day). Cortical excitability measures were obtained by transcranial magnetic stimulation. The clinical assessment included Kurtzke Functional System Scale (KFSS), 10-m walk test, and measures of disability (Expanded Disability Status Scale) and fatigue (Fatigue Severity Scale). Results Significant decrease in short interval intracortical inhibition (SICI) and increase in intracortical facilitation (ICF) were observed following steroids administration. The latter resulted also in a significant improvement in motor function, and a trend toward reduction in fatigue score and amelioration of sensory and cerebellar functions. No significant changes were found regarding disability or 10-min walk. Discussion Steroids might result in a very fast functional improvement in motor function by inducing ‘functional’ changes in the axonal membrane excitability, early before any ‘structural’ process of axonal regeneration and/or remyelination would take place. Steroids seem to modulate the intracortical synaptic plasticity by enhancing the intracortical glutamatergic facilitation and hampering the GABAergic inhibition. Conclusions During MS relapses, steroids could lead to functional improvement by modulating inhibitory and facilitatory cortical circuits. Significance SICI and ICF could serve as potential biomarkers for treatment response.