A portable hand-held device for quantifying and standardizing tremor assessment.

We describe the results of a hand-held device for quantifying tremor in the upper extremity. The specific aims of the study were to evaluate: (1) the reliability of the device to record tremor frequency and amplitude; (2) the relationship between observer ratings of tremor severity and spectral power derived from the instrument; (3) the effects of limb posture on tremor properties recorded by the instrument; and (4) whether scores from the instrument can discriminate types of tremor with sufficient accuracy to be of diagnostic value. Results from 242 subjects with tremor showed significant effects of limb posture on tremor frequency detected by the device which could not be revealed using traditional observer severity ratings. Subjects with tremor associated with idiopathic Parkinson's disease were distinguished from patients with drug-induced parkinsonian tremor with 83% accuracy. These and other findings on instrument validity demonstrate that tremor assessment can be performed using standard quantitative procedures which overcome many of the limitations inherent in subjective observer ratings. The portability of this instrument, referred to as the Tremorometer, makes it a useful tool for multi-site collaborative studies in community settings.