Diagnostic criteria for essential tremor and differential diagnosis.

Classic essential tremor (ET) is a condition in which the upper limbs (approximately 95% of patients) and, less commonly, the head (approximately 34%), face (approximately 5%), voice (approximately 12%), trunk (approximately 5%), and lower limbs (approximately 20%) exhibit a mixed postural and kinetic tremor without other neurologic abnormalities. Most patients with ET probably inherit the disease through an autosomal dominant gene, but the true ratio of hereditary versus sporadic ET is unknown. Isolated focal, position-specific, and task-specific tremors are probably not ET in most patients and are often due to subtle dystonia. Unilateral tremor, gait disturbance, rigidity, bradykinesia, rest tremor, and rapid onset of symptoms are indications of other tremorogenic disorders.