Description

• Essential tremor is a postural (occurring with voluntary maintenance of a position against gravity) or kinetic (occurring during voluntary movement) flexion–extension tremor that is slow and rhythmic and primarily affects the hands, forearms, head, or voice with a frequency of 4 to 12 Hz. Older patients tend to have lower frequency tremors, whereas younger patients exhibit frequencies in the higher range.
• The disease may be familial, sporadic, or associated with other movement disorders. Incidence and prevalence increase with age, but symptom onset can occur at any age. The tremor can be intermittent and exacerbated by emotional or physical stressors, fatigue, and caffeine.
• System(s) affected: neurologic, musculoskeletal, ear/nose/throat (ENT) (voice)

Epidemiology

Essential tremor is the most common pathologic tremor in humans.

Incidence
Can occur at any age, but bimodal peaks exist in the 2nd and 6th decades. Incidence rises significantly after age 49 years.

Prevalence
The overall prevalence for essential tremor has been estimated between 0.4% and 0.9% but is increased in older patients with an estimated prevalence of 4.6% at age 65 years and up to 22% at age 95 years.

Etiology and Pathophysiology

• Suspected to originate from an abnormal oscillation within thalamocortical and cerebello-olivary loops, as lesions in these areas tend to reduce essential tremor
• Essential tremor is not a homogenous disorder. Many patients have other motor manifestations and nonmotor features, including cognitive and psychiatric symptoms.

Genetics

• Positive family history in 50–70% of patients; autosomal dominant inheritance is demonstrated in many families with poor penetrance. Twin studies suggest that environmental factors are also involved.
• A link to genetic loci exists on chromosomes 2p22–2p25, 3q13, and 6p23. In addition, a Ser9Gly variant in the dopamine D₃ receptor gene on 3q13 has been suggested as a risk factor.

Commonly Associated Conditions

• Can be present in 10% of patients with Parkinson disease (PD); characteristics of PD that distinguish it from essential tremor include 3- to 5-Hz resting tremor; accompanying rigidity, bradykinesia, or postural instability; and no change with alcohol consumption
• Patients with essential tremor have a 4% risk of developing PD.
• Resting tremor, typically of the arm, may be seen in up to 20–30% of patients with essential tremor. Although action tremor is the hallmark feature of essential tremor, it is commonly found in patients with PD as well.