Voluntary motor function in patients with chronic fatigue syndrome

Introduction: The pathogenesis of chronic fatigue syndrome (CFS) remains un known. In particular, little is known of the involvement of the motor corte x and corticospinal system. Methods: Transcranial magnetic stimulation (TMS ) was used to assess corticospinal function in terms of latency and thresho ld of motor-evoked potentials (MEPs) in thenar muscles. Reaction times and speed of movement were assessed using button presses in response to auditor y tones. Results: Patients had higher (P<.05) self-assessed indices of fati gue (7/10) than for pain (5/10), anxiety (4/10) or depression (3/10). Mean (<plus/minus>S.E.M.) simple reaction times (SRTs) were longer (P<.05) in th e patients (275<plus/minus>19 ms) than in the controls (219 +/-9 ms); choic e reaction times (CRTs) were not significantly longer in the patients. Move ment times, once a reaction task had been initiated, were longer (P<.05) in the patients in both SRTs (patients, 248<plus/minus>13 ms; controls, 174 /-9 ms) and CRTs (patients, 269 +/- 13 ms; controls, 206 +/- 12 ms). There was no difference (P>.05) in threshold or latency of MEPs in hand muscles b etween the patients (threshold, 54.5 +/-2.2% maximum stimulator output [% M SG]; latency 22 +/-0.3 ms) and controls (threshold 54.6 +/-3.6% MSG; latenc y 22.9 +/-0.5 ms). Regression analysis showed no correlation (P>.05) of SRT s with either threshold for MEPs or fatigue index. Conclusion: Corticospina l conduction times and excitability were within the normal range despite a slower performance time for motor tasks and an increased feeling of fatigue . This suggests that the feeling of fatigue and the slowness of movement se en in CFS are manifest outside the corticospinal system. (C) 2001 Elsevier Science Inc. All rights reserved.