Kinetic tremor in a reach-to-grasp movement in Parkinson's disease

The aim of this study was to quantify the tremor of the hand during a natur al movement (kinetic tremor) in tremor-dominant parkinsonian patients (n = 13). We used a three-dimensional camera system to kinematically analyze res t and kinetic tremors in an unrestrained reach-to-grasp movement, and addit ional tremor recordings were performed under standard postural and rest con ditions using electromyography and accelerometry. The standard analysis sho wed a highly synchronized tremor with similar frequencies at rest and in su stained postural tasks, with and without loading. A kinematic recording was used to compare rest and action conditions. A strong inhibition of the res ting tremor was present at the onset of the movement and reached its peak d uring deceleration. A kinetic tremor of low amplitude was present in most o f the parkinsonian patients, but its occurrence was confined mainly to the terminal periods of the movement. The frequency of kinetic tremor was signi ficantly higher than that at rest, before the onset of the movement in Park inson's disease, as determined by the kinematic analysis (mean, 5.5 Hz vs 6 .5 Hz; p <0.01). Our results confirm similarities between the tremor at res t and the oscillations during a sustained postural task in classic parkinso nian tremor. In contrast to this stable tremor, which seems to be generated by basal ganglia oscillators, a different pathophysiology of oscillations during motion must be considered. The kinetic tremor is most likely related to an enhancement of the physiologic tremor in the terminal phase of the r each-to-grasp movement.