Fast orthostatic tremor in Parkinson's disease mimicking primary orthostatic tremor

Leg tremor during standing is a rare feature in idiopathic Parkinson's disease (PD). Tremor during standing usually has a low frequency (range, 4-6 Hz), similar to PD rest tremor frequency, and is improved by levodopa. We describe three cases of fast orthostatic tremor (FoT) of legs and trunk mimicking primary orthostatic tremor (OT) in patients treated with levodopa for PD. Asymmetrical akinetorigid syndrome was accompanied by a rest tremor in two cases. We obtained electrophysiological parameters by electromyographic (EMG) polygraphic recording after 16 hours withdrawal of antiparkinsonian treatment and at the maximal effect of levodopa in order to investigate the effect of dopaminergic stimulation upon such cases of orthostatic tremor in PD. Electrophysiological parameters of orthostatic tremor, especially frequency (range 14-18 Hz), were similar to that seen in POT. Severity of tremor was independent of seriousness and duration of PD. Levodopa had no effect either on the handicap due to OT or on the amplitude and frequency of the EMG OT activity. In contrast, mild improvement of OT was obtained with benzodiazepines in two cases and parkinsonian syndrome was levodopa-sensitive. These findings suggest that FoT in PD would not be directly controlled by the dopaminergic system. However, increased rhythmicities in basal ganglia or in cerebello-thalamic loops at the rapid frequencies range seen in PD could favor the emergence of a primary orthostatic tremor-like tremor in PD patients.