[A case of orthostatic tremor in parkinsonism]

A 79-year-old woman presenting with orthostatic tremor (OT) was reported. In addition to OT, neurological examination showed mild dementia, bradykinesia, rigidity of the neck and the upper limbs and positive Babinski reflex on the left. These clinical signs and CT as well as MRI findings suggested vascular parkinsonism as its pathological background. Upon standing with her feet together, she rapidly developed rhythmic repetitive contraction of all leg muscles. The shaking disappeared by walking, sitting, or lying down. The EMG recording revealed 4-Hz tremor which consisted of alternating contraction of anti-gravity muscles and their antagonists. The EMG bursts associated with the tremor were synchronous in corresponding muscles of both legs. OT could be bilaterally reset by unilateral voluntary or passive movement of leg. In the supine position, the tremor was not evoked by voluntary contraction of leg muscles against resistance. As the tremor was aggravated by the administration of haloperidol was suppressed by L-DOPA, it was thought to have the pharmacological basis common to the resting tremor of parkinsonism. Furthermore, we postulated that the postural tonus-regulating system, which is thought to set and maintain the tonus of antigravity muscles for standing upright, might be involved in the generation of the rhythmic discharge pattern (reciprocal bursts in a given leg and synchronized bursts in both legs) of OT.