Motion Characteristics of Subclinical Tremors in Parkinson’s Disease and Healthy Subjects

The Parkinson’s disease tremor characteristics reported previously are not applicable to the full spectrum of severity. The characteristics of high- and low-amplitude tremors differ in signal regularity and frequency dispersion, which indicates that characterization should be studied in separate severity. The subclinical tremor of Parkinson’s disease is close to physiological tremor, yet their distinctive features are still undetermined. This study aims to determine joint motion characteristics that are unique to subclinical Parkinson’s disease tremors. The tremors were characterized by four hand–arm motions based on displacement and peak frequencies. The rest and postural tremors of 63 patients and 62 normal subjects were measured with inertial sensors. The baseline was established from normal tremors, and the joint motions were compared within and between the two subject groups. Displacement analysis shows that pronation–supination and wrist abduction–adduction are the most and least predominant tremor motions respectively, for both Parkinson’s disease and normal tremors. However, the subclinical Parkinson’s disease has significant greater in amplitude and peak frequency in specific predominant motions as compared to normal tremor. The flexion-extension of normal postural tremor increases in frequency from proximal to distal segment, which is explainable by mechanical oscillation. This characteristic is also observed in patients but with amplification in wrist and elbow joints. The contributed distinctive characteristics of subclinical tremors provide clues on the physiological manifestation that is a result of the neuromuscular mechanism of Parkinson’s disease.