Zesiewicz et al practice and tertiary referral center found a bimodal distribu- tion only in the latter.10 It is possible that young patients with ET may more likely be referred to a tertiary referral center. Clinical characteristics of ET ET is considered to be heterogeneous condition with variable clinical expression in affected patients. It is characterized by a postural and/or kinetic tremor in the frequency range of 4 to 12 Hz. Tremor frequency generally decreases over time, while amplitude slowly increases. Alcohol transiently dimin- ishes tremor amplitude in 50% to 90% of cases, although this may worsen after the effect of alcohol has worn off. The location and amplitude of tremor in ET patients varies among patients. Approximately 90% of patients have tremor in their upper extremities, 30% have a head tremor, 20% have a voice tremor, 10% have a face or jaw tremor, and 10% of ET patients may have a lower limb tremor.11 Isolated head tremor is generally considered part of the clinical spectrum of ET. At least 50% of ET patients have tandem gait abnormalities.12 Recent studies have uncovered the presence on “nonmotor symptoms” including mild cognitive changes,13 depression, anxiety, social phobias, olfactory and hearing deficits that occur more frequently in ET patients than in normal age- matched controls. Diagnosis of eT ET is a clinical diagnosis, and there are currently no lab tests or radiological scans to aid in the diagnosis. Unfortunately, it is estimated that ET is misdiagnosed in 30% to 50% of cases.14,15 The consensus statement of the Movement Disorder Society on tremor includes the following clinical criteria for the diagnosis of ET.16 inclusion criteria 1. Bilateral postural tremor with or without kinetic tremor, involving hands and forearms, that is visible and persistent 2. Duration greater than 5 years exclusion criteria 1. Other abnormal neurological signs (except Froment’s sign) 2. Presence of known causes of increased physiological tremor 3. Concurrent or recent exposure to tremorogenic drugs or the presence of a drug withdrawal state 402 submit your manuscript | www.dovepress.com Dovepress Dovepress 4. Direct or indirect trauma to the nervous system within 3 months before the onset of tremor 5. Historical or clinical evidence of psychogenic origins 6. Convincing evidence of sudden onset or evidence of stepwise deterioration Deuschl and Elble proposed the following definition of three ET subtypes:17 1. Hereditary ET, for patients who fulfill consensus criteria for definite or classic ET and also have a family of at least one affected relative in the immediate family. The onset of tremor in the patient and the family member must occur prior to age 65 years. 2. Sporadic ET, for patients who fulfill the consensus criteria for definite or classic ET, but do not have an immediate family member with ET, and whose age at onset of ET is younger than 65 years. 3. Senile ET, for patients who have definite or classic ET according to consensus criteria, but who develop ET at or after the age of 65 years. Patients may or may not have a family history of ET. Another set of criteria for the diagnosis of ET may be found in the “The Washington Heights Inwood Genetic Study of Essential Tremor”.18 These criteria include: 1. On examination, a +2 postural tremor* in at least one arm (a head tremor might also be present, but is not sufficient for the diagnosis) 2. On examination, there must be a +2 kinetic tremor dur- ing at least four tasks, or a +2 kinetic tremor on one task and a +3 kinetic tremor on a second task. Tasks include pouring water, using a spoon to drink water, drinking water, finger-to-nose maneuver, and drawing spirals 3. If on examination the tremor is present in the dominant hand, then by report it must interfere with at least one activity of daily living (eating, drinking, writing or using the hands). If on examination the tremor is not present in the dominant hand, then this criterion is irrelevant 4. Medications, hyperthyroidism, ethanol, and dystonia are not potential etiological factors 5. Symptoms are not psychogenic (eg, bizarre features, fea- tures inconsistent in character, the patient is distractable, or other psychiatric features on examination) For these criteria, the following scale is used: 0 – No visible tremor 1 – Tremor is of low amplitude, barely perceivable, or intermittent 2 – Tremor is of moderate amplitude (1–2 cm) and usu- ally present, and is clearly oscillatory Neuropsychiatric Disease and Treatment 2010:6