Superficial brain stimulation in multiple sclerosis.

Central motor conduction time (CMCT) is the most frequently studied measure derived from transcranial magnetic stimulation (TMS) in multiple sclerosis (MS); it is abnormal in 57-93% of patients. Addition of the triple stimulation technique and combining motor with other evoked potentials (EPs) increases sensitivity. Cross-sectional correlations of TMS measures with clinical assessments of motor dysfunction or global disability are high. Longitudinally, CMCT is sensitive to both worsening and improvement of motor function, showing its potential to detect therapeutic responses. Moreover, combined multimodal EPs are valid quantitative predictors of the clinical course over periods ranging from 2 to 14 years. Measures of transcallosal connectivity (ipsilateral silent period and interhemispheric inhibition) are altered even in early MS, and yield complementary information on subclinical changes. Pathological brain plasticity in MS has been demonstrated by paired associative stimulation studies revealing a compensatory role of the ipsilateral motor and premotor areas. Central motor fatigue is associated with reduced motor EP amplitudes and increased cortical silent periods in normal controls, whereas patients with MS suffering from subjective fatigue show various abnormalities in cortical modulation of the motor system.