Tremor.

Tremor, a rhythmic, involuntary, oscillatory movement of body parts, is the most common movement disorder. Tremors are classified as rest or action tremors. Rest tremor occurs when the affected body part is completely supported against gravity. Action tremors are produced by voluntary muscle contraction and are further divided into postural, isometric, or kinetic tremors. This article describes clinical signs and symptoms of six tremor syndromes, including physiologic tremor, essential tremor, Parkinson's disease, toxic and drug-induced tremor, cerebellar tremor, and psychogenic tremor, and presents a detailed diagnostic approach to tremor. Although new technologies such as positron emission tomography and single photon emission computed tomography are under investigation for possible use in diagnosing specific tremor syndromes, they have no widespread applicability or use at this time. The history and physical examination remain the most important diagnostic tools available to clinicians in identifying and classifying tremor syndromes.