Clinical correlates of action tremor in Parkinson disease

Background: Action tremor is often noted in patients with Parkinson disease (PD), yet the clinical correlates of this type of tremor have been the foc us of few studies. It is not clear whether this action tremor is a manifest ation of the underlying basal ganglia disease. Objective: To determine whether the severity of action tremor in PD is asso ciated with age, age at disease onset, disease duration, levodopa dose, sev erity of rest tremor, or other motor (ie, bradykinesia, rigidity) and nonmo tor manifestations of PD. Methods: Patients with PD (N = 197) were ascertained as part of a familial aggregation study. All patients underwent a neurological examination. Rest tremor was rated with the Unified Parkinson Disease Rating Scale; and actio n tremor, with the Washington Heights-Inwood Genetic Study of Essential Tre mor Rating Scale. Results: Action tremor was present in 184 (93.4%) of 197 patients. Four pat ients (2%) met criteria for definite essential tremor. The action tremor sc ore was not associated with age, age at onset, or disease duration. The act ion tremor score was associated with the rest tremor score (r = 0.37; P < . 001), and more strongly with the ipsilateral than contralateral rest tremor score. The association between the action tremor score and the rest tremor score was diminished but still significant (r = 0.21, P < .02) even when w e excluded these 63 patients with re-emergent tremor. Neither the action no r the rest tremor score was associated with the bradykinesia or rigidity sc ores, Hoehn and Yahr scale score, or modified Mini-Mental State Examination score. Conclusions: Action tremor was associated with rest tremor in PD, suggestin g that, at least in part, action tremor is a manifestation of the underlyin g basal ganglia disease. Neither tremor was associated with other motor and nonmotor manifestations of PD. This in turn suggests that tremor in PD may represent an underlying pathophysiological process different from these ot her manifestations.