Essential tremor: phenotypes.

Classically, essential tremor (ET) was defined by the Movement Disorder Society Consensus Statement on Tremor (1998) as "a bilateral, largely symmetric postural or kinetic tremor involving hands and forearms that is visible and persistent". Additional or isolated tremor of the head may occur but in the absence of abnormal posture. Duration is more than 5 years and the neurological examination is normal, with exception of the cogwheel phenomenon. In the last years ET has evolved into two different meanings. First of all, the classical ET, as a monosymptomatic disorder, and second, a heterogeneous disorder, the Essential Tremors, or a family of diseases. Nowadays, ET can be classified with both motor and non-motor elements. Tremor may occur also in the legs, feet, trunk, jaw, chin, tongue, and voice. Although postural and kinetic tremors are the main features of ET, intentional tremor and tremor at rest may also occur in some patients. Other motor features described in patients with ET are gait ataxia, postural instability and eye-motion abnormalities. Non-motor features include cognitive (memory and executive problems and dementia), psychiatric (anxiety, depression and social phobia), and sensory abnormalities (olfactory deficits, hearing loss).