Fatigue in hypokinetic, hyperkinetic, and functional movement disorders

The emerging science of fatigue has soundly endorsed the need for its unified definition, shared terminology and increased recognition in neurological illnesses. Nevertheless, the real impact of fatigue remains under-recognized. Fatigue describes a sense of tiredness, lack of energy or need for increased effort often perceived as overwhelming, pervasive, and disabling. It is a common feature of chronic medical conditions and neurological diseases, including Parkinson's disease (PD) and other hypokinetic, hyperkinetic, and functional movement disorders (FMD). While there is solid evidence for the burden of fatigue in PD, knowledge of fatigue in other movement disorders (MDS) is still limited. Lack of consensus definition, rigorous measures and the high prevalence of potential confounders such as apathy, depression and sleepiness are the main obstacles in studying fatigue in MDS. This review of the prevalence, impact, and clinical correlates of fatigue in common MDS summarizes current hypotheses for the pathophysiological mechanisms underlying fatigue and gives a brief overview of treatment options. Fatigue is a prevalent, disabling, primary non-motor symptom (NMS) in MDS, including atypical and secondary parkinsonisms, dystonia, essential tremor (ET) and a hallmark feature of FMD. We report the hypothesis that fatigue is a perceptual disorder of the sensorimotor system. Given the relevance of this burdensome symptom, fatigue deserves greater clinical and research attention to better understand its manifestation and pathophysiology and to improve diagnosis and treatment.