Fatigue in patients with multiple sclerosis: from movement preparation to motor execution.

Background: The neural mechanisms underlying fatigue in multiple sclerosis (MS) are still poorly understood. Cortico-cortical and cortico-subcortical circuitry abnormalities may play a central role in its pathogenesis. Our previous studies suggest that central fatigue may be related to an impairment of volition drive during movement preparation.

Objective: We further explored the central mechanisms of fatigue at the premovement level in MS patients during a sustained motor task.

Methods: In MS patients with (MS-F) and without (MS-NF) fatigue and age-matched healthy controls, we evaluated the motor cortex excitability and the premovement facilitation (PMF) through transcranial magnetic stimulation before and after 5min of sequenced finger-tapping movements at a fixed frequency of 2Hz.

Results: In MS-F patients, the number of correct sequences performed and the ability to keep a fixed movement rate during the 5-min motor task were significantly decreased in comparison to the normal controls and MS-NF patients. Also, in MS-F patients, post-exercise PMF was significantly decreased. The PMF abnormalities were highly correlated with the performance decay.

Conclusions: PMF may be considered as a kind of servo-mechanism which could play a crucial role during sustained motor task in order to prevent motor performance disruption and to avoid motor exhaustion.