There are 2 distinct postural tremor phenotypes in Parkinson disease (PD), which have a different pathophysiology and require different treatment, according to a recent study. The first type, re-emergent tremor, is a continuation of resting tremor during stable posturing, and it has a dopaminergic basis. The second, pure postural tremor, is a less common type of tremor that is inherent to PD, but has a largely non-dopaminergic basis. In this combined observational and intervention study, researchers measured resting and postural tremor characteristics in 73 patients with tremulous PD by using EMG of forearm muscles. They performed an automated 2-step cluster analysis on 3 postural tremor characteristics: frequency difference with resting tremor, degree of tremor suppression after posturing, and dopamine response. They found:

• 81% had re-emergent tremor and 19% had pure postural tremor.
• This finding was manually validated (accuracy of 93%).
• Pure postural tremor was not associated with clinical signs of essential tremor or dystonia, and it was not influenced by weighing.