An objective measure combining physical and cognitive fatigability: Correlation with subjective fatigue in Parkinson's disease

Background Objective measures of physical and cognitive fatigability do not correlate with subjective Parkinson's disease (PD)-related fatigue. The relationship of subjective PD-related fatigue to tasks combining cognitive and motor effort has never been explored. Methods Forty-four right-handed, non-demented PD patients, 22 with (PD-F) and 22 without (PD-NF) fatigue, were tested using a sensor-engineered glove on their more affected hand. Patients performed sequential opposition finger movements following a metronome at 2\ua0Hz for 5\ua0min (cued task), and for another minute following a 2-min rest. The same task was repeated without sustained auditory cueing. Movement time (inter-tapping interval, ITI) and rate, touch duration, percentage of correct sequences and clinical measures (motor and fatigue severity, depression, sleep impairment and apathy) were analysed. Results In the cued task, motor performance worsened over time (significantly increased ITI and decreased movement rate on the third to fifth minute) in PD-F patients only. In the uncued task, motor performance deteriorated similarly in the two groups. PD-F and PD-NF patients differed in ITI and movement rate deterioration over time only in the cued task, independently from motor severity, depression and sleep impairment. The severity of subjective fatigue complaints significantly correlated with motor performance deterioration in the cued task. Conclusions PD-related fatigue is associated with performance on an externally cued, attention-controlled motor task, but not with an uncued version of the same task. The finding supports a link between PD-related fatigue and attention-demanding motor tasks, proposing a model of inducible fatigue applicable to future clinical and neuroimaging research