Deficit in motor performance correlates with changed corticospinal excitability in patients with chronic fatigue...

Chronic fatigue syndrome (CFS) is characterised by fatigue and musculosketetal pain, the severity of which is variable. Simple reaction times (SRTs) and movement times (SMTs) are slowed in CFS. Our objective is to correlate the day-to-day changes in symptomatology with any change in SRT, SMT or corticospinal excitability. Ten CFS patients were tested on two occasions up to two years apart. Motor evoked potentials (MEPs) to transcranial magnetic stimulation (TMS) of the motor cortex were recorded from the thenar muscles. Threshold TMS strength to evoke MEPs was measured to index corticospinal excitability. SRTs and SMTs were measured. The percentage change in both SRTs and SMTs between the two test sessions correlated with the percentage change in corticospinal excitability assessed according to threshold TMS intensity required to produce MEPs. This study provides evidence that changing motor deficits in CFS have a neurophysiological basis. The slowness of SRTs supports the notion of a deficit in motor preparatory areas of the brain.