Differentiation and diagnosis of tremor.

Tremor, an involuntary, rhythmic, oscillatory movement of a body part, is the most common movement disorder encountered in clinical practice. Rest tremors occur in a body part that is relaxed and completely supported against gravity. Action tremors occur with voluntary contraction of a muscle and can be further subdivided into postural, isometric, and kinetic tremors. All persons have low-amplitude, high-frequency physiologic tremors at rest and during action that are not reported as symptomatic. The most common pathologic tremor is essential tremor. In one-half of cases, it is transmitted in an autosomal dominant fashion, and it affects 0.4 to 6 percent of the population. More than 70 percent of patients with Parkinson disease have tremor as the presenting feature. This tremor is typically asymmetric, occurs at rest, and becomes less prominent with voluntary movement. Features consistent with psychogenic tremor are abrupt onset, spontaneous remission, changing tremor characteristics, and extinction with distraction. Other types of tremor are cerebellar, dystonic, drug- or metabolic-induced, and orthostatic. The first step in the evaluation of a patient with tremor is to categorize the tremor based on its activation condition, topographic distribution, and frequency. The diagnosis of tremor is based on clinical information obtained from a thorough history and physical examination. For particularly difficult cases, single-photon emission computed tomography to visualize the integrity of the dopaminergic pathways in the brain may be useful to diagnose Parkinson disease.