Objective: To evaluate the validity of force estimation as a method for assessing proprioception, and to determine if proprioception is impaired in Parkinson’s disease (PD) patients using this method.

Background: Proprioception plays a crucial role in motor planning. Sensory integration within the basal ganglia, which depends on dopamine, is thought to be impaired in PD. Despite this, current proprioception assessments remain largely subjective.

Method: We conducted a prospective pilot study to assess the ability of PD patients and healthy controls to estimate applied force during a handgrip test, and compared it with the “thumb localizing test,” a conventional proprioception assessment. Consecutive PD patients with Hoehn & Yahr stages 1-3, and no other known causes of proprioceptive deficit, were included. Participants performed a maximal voluntary contraction (MVC) using a digital handgrip dynamometer. After training with visual feedback, they were asked to blindly perform a 50% contraction. This force estimation was then compared to the thumb localizing test, which was repeated 20 times to ensure consistency and expressed as the percentage of correct trials. Pearson correlation was used to assess the relationship between both tests, as well as their correlation with MDS-UPDRS III scores. Mean and standard deviation comparisons were made between PD patients and healthy controls.

Results: Twenty-three PD patients and 17 healthy controls were evaluated. PD patients showed weaker MVCs compared to controls (22.27 vs 34.57 kg; p<0.0001), and a weaker handgrip when trying to estimate 50% CVM (45% vs 52%; p=0.08). A significant direct correlation was found between the 50% force estimation and the thumb localizing test (R=0.32; p=0.04). MDS-UPDRS III showed a trend toward an inverse correlation with force estimation (R=-0.35; p=0.09).

Conclusion: Our results demonstrate a significant correlation between the thumb localizing test, an established method for evaluating proprioception, and the 50% force estimation test. This suggests that force estimation could serve as a simple, quantitative tool for assessing proprioception. Additionally, our findings indicate that PD patients have impaired proprioception and tend to overestimate the applied force.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/force-estimation-as-a-method-to-assess-proprioception-in-parkinsons-disease-patients/