Motor cortex excitability in chronic fatigue syndrome

Objective: To use transcranial magnetic stimulation (TMS) to define motor c ortical excitability in chronic fatigue syndrome (CFS) subjects during a re petitive, bilateral finger movement task. Methods: A total of 14 CFS patients were tested and compared with 14 age-ma tched healthy control subjects. TMS of the motor cortex (5% above threshold ) was used to elicit motor evoked potentials (MEPs). Subjects performed reg ular (3-4/s) repetitive bilateral opening-closing movements of the index fi nger onto the thumb. MEPs of the first dorsal interosseus (FDI) were measur ed before, immediately following exercise periods of 30, 60 and 90 s, and a fter 15 min of rest. Results: Performance, defined by rate of movement, was significantly slower in CFS subjects (3.5/s) than in controls (4.0/s) independent of the hand m easured. The rate, however, was not significantly affected by the exercise duration for either group. The threshold of TMS to evoke MEPs from the FDI muscle was significantly higher in CFS than in control subjects, independen t of the hemisphere tested. A transient postexercise facilitation of MEP am plitudes immediately after the exercise periods was present in controls ind ependent of the hemisphere tested, but was absent in CFS subjects. A delaye d facilitation of MEPs after 15-30 min of rest was restricted to the non-do minant hemisphere in controls; delayed facilitation was absent in CFS subje cts. Conclusions: Individuals with CFS do not show the normal fluctuations of mo tor cortical excitability that accompany and follow non-fatiguing repetitiv e bimanual finger movements. (C) 2000 Elsevier Science Ireland Ltd. All rig hts reserved.