The dynamics of resting and postural tremor in Parkinsonʹs disease

Objective: The study examines the time and frequency structure of Parkinsonʹs disease tremor in patients that exhibit no clinical signs of tremor. Methods: Eight mild to moderate Parkinsonʹs disease and 8 matched control subjects maintained their limb in a constant position (30 s) under a postural finger, postural hand and resting tremor condition. Finger acceleration from the middle phalange, electromyographic (EMG) activity from extensor digitorum communis and flexor digitorum superficialis (FDS) were recorded. Results: The data confirmed that there were no differences in the amount of limb motion and the modal frequency was around 9 Hz for each subject group. The time-dependent organization of tremor was more regular (lower approximate entropy [ApEn]) in Parkinsonʹs disease. Both time and frequency analyses between the acceleration and extensor EMG signals demonstrate a reduction in the 20–25 Hz tremor component and an increase in the 8–12 Hz region of tremor. Conclusions: The results are discussed in relation to the proposal that increased regularity results from an increase in motor unit synchronization at 8–12 Hz and a reduction in the amplitude of the 20–25 Hz tremor component. The time and frequency structure of tremor may be useful in assessing individuals with Parkinsonʹs disease.