Fatigue in Parkinson's disease: motor or non-motor symptom?

Fatigue is one of the most disabling symptoms in patients with Parkinson's disease (PD), with a significant impact on patients' quality of life. Clinical studies using ad hoc questionnaires showed that in PD fatigue is associated with non-motor as well motor symptoms. Neurophysiological observations suggest that motor mechanisms play a role in the pathophysiology of fatigue but there is no clear correlation between fatigue measured with clinical instruments and fatigue assessed with neurophysiological tests. Neuroimaging studies show that fatigue is associated with an involvement of non-dopaminergic or extrastriatal dopaminergic pathways. It is conceivable that both motor and non-motor mechanisms underlie the pathophysiology of fatigue.