Impairments in precision grip force control in individuals with Parkinson's disease

Purpose. The purpose of our study is to identify impairments in fine motor control in individuals with Parkinson's disease (PD) during a force-tracking task using force sensors and comparing that to the fine motor control in age-matched controls. We also observed differences in fine motor coordination across a spectrum of patients with varying severity of disease. Methods. 30 subjects with Parkinson's disease and 30 age-matched controls participated. Commercially available six-axes force sensors were used to provide an interface for interaction between the subject and the force-tracking task. Subjects tracked a moving sine wave on a computer screen by controlling the amount of force exerted between their index finger and thumb. The two digits were attached to the force sensors that are capable of recording the amounts of force exerted by the subject. During a part of the task, a simultaneous mental activity was introduced and the effect of this distraction was evaluated. Performance of the task was also evaluated using a pseudorandom wave for another three minutes including the distraction components. Results. We compared results between subjects and controls using univariate analysis of variance. Association between the motor score of the Unified Parkinson's disease Rating Scale (UPDRS) and the force tracking variables as well as that between the force tracking variables and chronicity of the disease was evaluated using multiple regression analyses. Individuals with PD showed greater amounts of error, lesser coordination and greater amounts of lag compared to controls. Distraction significantly affected individuals with PD to a greater extent compared to controls. The test showed no association with chronicity of the disease and showed a moderate association to function based on the UPDRS. Clinical relevance. Deficient hand function in activities that involve fine motor coordination is one of the chief complaints of individuals with Parkinson's disease. The ability to perform activities that involve precision grip depends on the capacity to make fine adjustments to forces in response to the demands placed by complex environments with a number of distractions. Individuals with PD performed with greater deficits on our test especially during the distraction component of the task.