Tremor: Sorting Through the Differential Diagnosis.

Tremor is an involuntary, rhythmic, oscillatory movement of a body part. It is the most common movement disorder encountered in primary care. The diagnosis of tremor is based on clinical information obtained from the history and physical examination. The most common tremors in patients presenting to primary care physicians are enhanced physiologic tremor, essential tremor, and parkinsonian tremor. All persons have low-amplitude, high-frequency physiologic tremors at rest and during action that are not reported as symptomatic, but can be enhanced by anxiety, medication use, caffeine intake, or fatigue. Features consistent with psychogenic tremor are abrupt onset, spontaneous remission, changing tremor characteristics, and extinction with distraction. Other types of tremor include cerebellar, dystonic, and drug- or metabolic-induced. The first step in evaluating a patient with tremor is to categorize the tremor based on its activation condition, topographic distribution, and frequency. Resting 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. The most common pathologic tremor is essential tremor, which affects 0.4% to 6% of the population. In one-half of cases, it is transmitted in an autosomal-dominant fashion. More than 70% of patients with Parkinson disease have tremor as the presenting feature. This tremor is typically unilateral, occurs at rest, and becomes less prominent with voluntary movement. If there is diagnostic uncertainty, single-photon emission computed tomography can be used to visualize the integrity of the dopaminergic pathways in the brain, and transcranial ultrasonography may be useful to diagnose Parkinson disease.