Voluntary motor function in patients with chronic fatigue syndrome.

INTRODUCTION

The pathogenesis of chronic fatigue syndrome (CFS) remains unknown. In particular, little is known of the involvement of the motor cortex and corticospinal system.

METHODS

Transcranial magnetic stimulation (TMS) was used to assess corticospinal function in terms of latency and threshold of motor-evoked potentials (MEPs) in thenar muscles. Reaction times and speed of movement were assessed using button presses in response to auditory tones.

RESULTS

Patients had higher (P<.05) self-assessed indices of fatigue (7/10) than for pain (5/10), anxiety (4/10) or depression (3/10). Mean (+/-S.E.M.) simple reaction times (SRTs) were longer (P<.05) in the patients (275+/-19 ms) than in the controls (219+/-9 ms); choice reaction times (CRTs) were not significantly longer in the patients. Movement times, once a reaction task had been initiated, were longer (P<.05) in the patients in both SRTs (patients, 248+/-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 between the patients (threshold, 54.5+/-2.2% maximum stimulator output [% MSO]; latency 22+/-0.3 ms) and controls (threshold 54.6+/-3.6% MSO; latency 22.9+/-0.5 ms). Regression analysis showed no correlation (P>.05) of SRTs with either threshold for MEPs or fatigue index.

CONCLUSION

Corticospinal 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 seen in CFS are manifest outside the corticospinal system.