[Fatigability and weakness from a neurological viewpoint]

Fatigue is a frequent but ill defined symptomatology in many disorders of the central and the peripheral nervous system. It is characterized as a fluctuating incapacity or weakness, often in the absence of overt paresis. Experimental or diagnostic evidence of fatigue is available only in disorders of the peripheral motor neuron, the neuromuscular junction and the muscle fibers, but not in CNS disorders. Fatigue, as a fluctuating symptomatology may be misdiagnosed as simulation or malingering not only by lay persons, but also by doctors.