Essential Tremor Syndrome

Description

• 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 and 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.
• 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 include neurologic, musculoskeletal, ear/nose/throat (ENT) (voice)

Epidemiology

Essential tremor is the most common pathologic tremor in humans.

• 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 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.

• 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.