Definition
- Essential tremor (ET) is a high-frequency (up to 12 Hz), primarily postural tremor.
- Predominantly affects the upper extremities
- Usually mild, and many patients do not seek medical attention.
- Importance stems from:
- Need to distinguish it from pathologic causes of tremor, notably Parkinson’s disease (PD)
- Small percentage of patients with ET (between 5 and 15%) who have more severe symptoms and some degree of disability
Epidemiology
- Prevalence
- Most common tremor disorder
- Most common involuntary movement disorder
- 0.4–3.9% of the general population affected
- Affects 5–10 million individuals in the U.S.
- Age
- Prevalence increases with age.
- Peak periods of onset are the third and sixth decades of life.
- Can occasionally present in childhood
- 4–5% > age 40 have ET.
Risk Factors
- Family history of ET
- Persons with a first-degree relative with ET are ~5 times more likely than the general population to be affected.
Etiology
- Etiology is unknown.
- Genetic factors play an important role.
- ~50% of patients have a positive family history with an autosomal dominant pattern of inheritance.
- Studies of monozygotic twins show importance of environmental factors as well.
- Pathophysiology
- Cerebellum and inferior olives have been implicated as possible sites of a “tremor pacemaker.”
- Thalamic involvement is evidenced by response to surgical interventions in this area.
- Postmortem studies have failed to find a consistent pattern of neuropathology.
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