DECREASED POSTEXERCISE FACILITATION OF MOTOR EVOKED-POTENTIALS IN PATIENTS WITH CEREBELLAR DEGENERATION

We studied the effects of exercise an motor evoked potentials (MEPs) e licited by transcranial magnetic stimulation (TMS) in 18 normal (contr ol) subjects and II medication-free patients with cerebellar degenerat ion. Subjects performed repealed sets of isometric exercise of the ext ensor carpi radialis muscle until the muscle fatigued (subject became unable to maintain half maximal force). MEPs were recorded before and after each exercise set and for up to 30 minutes after the last set. T he mean amplitude of MEPs recorded from the resting muscle immediately after each exercise set was 218% of the mean preexercise MEP amplitud e in normal subjects and 132% in cerebellar patients, indicating poste xercise MEP facilitation in both groups. However, postexercise MEP fac ilitation, compared with the mean preexercise MEP amplitude, was not s ignificant in the patients but was significant in the normal subjects. The amplitudes of MEPs recorded within the first few minutes after fa tigue were 44% of the mean preexercise MEP amplitudes in both groups. We conclude that in patients with cerebellar degeneration, postexercis e MEP facilitation is significantly reduced, whereas postexercise MEP depression after fatigue is similar to that of normal subjects.