Background The Expanded Disability Status Scale (EDSS) is the most widely used measure of disability in MS, however because of its limitations surrogate markers of clinical disability progression are of high interest. Transcranial magnetic stimulation (TMS) measures of demyelination and cortical excitability correlate with disability levels in MS. Objective Aim of this study was testing whether paired pulse (pp) TMS represents a reliable surrogate marker to measure clinical disability in MS. Methods ppTMS measures of intracortical synaptic transmission such as short interval intracortical inhibition (SICI), long interval intracortical inhibition (LICI), short interval intracortical facilitation (SICF) and intracortical facilitation (ICF) were collected from 74 patients affected by MS. Correlation of EDSS scores with ppTMS measures was analyzed. Results EDSS scores correlated with patient’s age, disease duration, Motor Evoked Potentials latency and thresholds and SICF measures but not with age of onset, SICI, ICF and LICI. Conclusions These findings support a possible use of SICF and MEP latency as surrogate markers of disability in MS. Further research is warranted to determine the role of SICF in the follow up of disease progression and to validate its use as an endpoint in multiple sclerosis clinical trials.
