Orthostatic tremor - a review.

Orthostatic tremor (OT) is a rare syndrome characterized by unsteadiness on standing due to a high-frequency tremor involving the legs. Symptoms usually start in the sixth decade. Typically, the symptoms rapidly improve on sitting or walking, and the need to sit down or to move can be so strong that patients avoid situations where they have to stand still. A polygraphic recording of a fast and synchronous tremor of the legs, between 13 and 18Hz, is mandatory to confirm the diagnosis of OT. Many patients also suffer from tremor, often involving lower frequencies, of the face, hands, or trunk. Recent studies suggest that this is perhaps due to subharmonics of the high-frequency tremor spreading through the body. Most cases of OT seem to be idiopathic, though symptomatic forms have been occasionally described. Several cases of OT have been reported in Parkinson's disease (PD), either preceding the onset of OT or developing in long-standing PD, suggesting a dopaminergic control of the central oscillator, possibly in the posterior fossa. The response to treatment is often disappointing. Clonazepam is widely used as a first-line agent, but gabapentin and dopaminergic drugs may be helpful in some patients.