Essential tremor and its variants.

Essential tremor is the commonest of movement disorders. Although sometimes prefaced with the term 'benign', it often causes significant disability. Diagnosis is based on the clinical finding of a postural tremor, predominantly affecting the upper limbs, that is absent at rest and not associated with extrapyramidal or cerebellar signs. There are, as yet, no specific anatomical, physiological, biochemical or genetic markers for the condition. Postural limb tremors, clinically indistinguishable from essential tremor, may occur in patients who have, or will later develop, other neurological conditions; whether such patients have essential tremor is a matter of controversy that will only be resolved with a better understanding of the pathophysiology of essential tremor. Positron emission tomography in patients with essential tremor reveals increased cerebellar activity even at rest, a finding that is consistent with the cerebellum having an important role in the generation of tremor. Abnormal cerebellar function has also been invoked to account for the abnormal manner in which patients with essential tremor perform rapid voluntary wrist movements. Molecular genetic studies in hereditary essential tremor have been initiated, but with negative results so far. Several new drug treatments have been tried, but with limited success; the role of thalamic stimulation and botulinum toxin in the treatment of essential tremor remains to be judged.