A practical guide to the differential diagnosis of tremor.

Tremor is, by definition, a rhythmic oscillation of a body part. It is the most prevalent movement disorder in clinical medicine, so doctors working in many specialities and in general practice can expect to encounter it. Most tremors can be classified on the basis of four observable clinical characteristics: anatomical pattern; the relative prominence of the tremor at rest, on maintaining a posture, and with action; tremor frequency; and tremor amplitude. A resting tremor suggests Parkinson's disease, and the diagnosis then depends on a judgement about whether the patient has other signs of parkinsonism. The most common causes of postural tremor are physiological tremor, essential tremor and drug-induced tremor. The differential diagnosis may also include dystonic tremor and psychogenic tremor, while metabolic tremor caused by thyrotoxicosis should be considered in any recent-onset postural tremor. Wilson's disease and fragile X-associated tremor/ataxia syndrome are rarer conditions that may present with tremor and are very important to identify. There is a small but genuine diagnostic grey zone between Parkinson's disease and more benign tremor disorders such as essential tremor and dystonic tremor, in which resting and postural tremor coexist with mild or equivocal non-tremor parkinsonian signs. The authors review clinical features and investigational techniques that may help to discriminate this group of hard-to-classify tremors.