["Primary" orthostatic tremor. 10 clinical electrophysiologic observations]

Orthostatic tremor is an unusual kind of potentially disabiling tremor appearing immediately when standing. Clinical examination is normal in primary form except for wide base standing and unsteadiness which disappear when walking. Arm tremor resembling essential tremor is found present in one third of cases. Electrophysiological exploration is necessary for diagnosis and shows a regular rapid tremor (frequency around 16 Hz). We present 10 new cases, 3 men and 7 women, 37 to 74 years old. Unsteadiness when standing was the predominant complaint in 9 cases, the other first described pains in the lower limbs. All had visible or palpable tremor predominant in thighs. Four patients had postural arm tremor, one had neurogen syndrome in the lower limbs corresponding to toxic polyneuropathy which developed after tremor. Electromyographic study found high frequency (13-17.3 Hz) rhythmic discharge in weight-bearing muscles. Orthostatic tremor cannot be considered as a clinical variant of postural essential tremor. Its pathophysiology is unknown but the efficacy of clonazepam, primidone or barbiturates suggests the impairment of the gabaergic system.