Can somatosensory evoked potentials predict disease course in early multiple sclerosis patients?

BACKGROUND Multiple sclerosis (MS) is an autoimmune degenerating disease, where myelin degradation as well as axonal loss is present. PURPOSE To asses whether recording the middle-latency components of the median nerve somatosensory evoked potentials (SEPs) increases the diagnostic sensitivity in patients with MS, and to investigate whether any of the abnormalities correlates with the severity of the clinical signs and predicts future outcome. METHODS Twenty consecutive MS patients at early onset were included. Median and tibial nerve SEPs were recorded at the time of the referral. Extended Disability Status Scale (EDSS) and Multiple Sclerosis Severity Score (MSSS) were assessed at the time of the referral and after 5-year followup. RESULTS Recording the middle-latency components increased the sensitivity of the median nerve SEPs from 50% to 75%. The overall sensitivity of the SEPs (i.e. including also tibial nerve SEPs) modestly increased (from 80% to 90%). The amplitude of the cortical N20 potential of the median nerve was inversely correlated to the clinical severity. None of the parameters could predict the future outcome. CONCLUSIONS Our results provide neurophysiological evidence for the role of axonal lesions in the clinical disability of the patients with MS.