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Essential Tremor Syndrome

BASICS

DESCRIPTION

  • Postural or kinetic flexion-extension tremor, slow and rhythmic (4–12 Hz).
  • Commonly affects hands, forearms, head, voice.
  • Older patients tend to have lower frequency tremors.
  • Familial (autosomal dominant) or sporadic; onset can occur at any age.
  • Tremor can worsen with emotional or physical stress, fatigue, caffeine.

EPIDEMIOLOGY

  • Most common pathologic tremor in humans.
  • Bimodal incidence peaks in 2nd and 6th decades; increases after 49 years.
  • Prevalence: 0.4–0.9% general population; up to 4.6% at age 65, 22% at age 95.

ETIOLOGY AND PATHOPHYSIOLOGY

  • Abnormal oscillations in thalamocortical and cerebello-olivary loops.
  • Heterogeneous disorder with motor and nonmotor features including cognitive and psychiatric symptoms.
  • Genetics: positive family history in 50-70%; autosomal dominant with incomplete penetrance.
  • Associated loci: chromosomes 2p22-2p25, 3q13, 6p23; dopamine D3 receptor gene variant Ser9Gly.

COMMONLY ASSOCIATED CONDITIONS

  • May coexist in 10% of Parkinson disease patients.
  • Parkinson disease features distinguishable by resting tremor (3–5 Hz), rigidity, bradykinesia, no alcohol response.
  • Resting tremor present in 20-30% of essential tremor cases.

DIAGNOSIS

HISTORY

  • Bilateral action or postural tremor of hands and forearms, possibly head/voice/lower limbs.
  • Duration ≥3 years.
  • Absence of other neurological signs except cogwheel phenomenon.
  • Secondary criteria: family history, alcohol responsiveness.

PHYSICAL EXAM

  • Tremor primarily affects upper limbs (~95%).
  • Less commonly head (34%), lower limbs (30%), voice (12%), tongue, face, trunk.

DIFFERENTIAL DIAGNOSIS

  • Parkinson disease
  • Enhanced physiologic tremor
  • Wilson disease
  • Hyperthyroidism
  • Multiple sclerosis
  • Dystonic tremor
  • Cerebellar tremor
  • Asterixis
  • Psychogenic tremor
  • Orthostatic tremor
  • Drug-induced tremor (amiodarone, SSRIs, steroids, lithium, β-agonists, etc.)

DIAGNOSTIC TESTS

  • No specific biomarker or test for essential tremor.
  • Rule out Wilson disease (ceruloplasmin, serum copper), thyroid dysfunction (TSH).
  • Brain MRI not routinely indicated unless suspicion for central lesion.
  • Accelerometry: essential tremor frequency 5–8 Hz; Parkinson’s 4–6 Hz.
  • Surface EMG less useful for differentiation.

TREATMENT

GENERAL MEASURES

  • Treatment indicated when tremor affects daily function or causes distress.

MEDICATION

First Line

  • Propranolol 60–320 mg/day: reduces tremor magnitude ~50%; 70% show clinical improvement.
  • Primidone 25 mg bedtime, titrated to 150–300 mg: reduces tremor amplitude 40-50%.
  • Both have similar efficacy; ~30-50% nonresponders.

Second Line

  • Topiramate (up to 400 mg/day) and gabapentin (up to 400 mg TID).
  • Alternative β-blockers: sotalol, nadolol, atenolol (less evidence).
  • Benzodiazepines (clonazepam, alprazolam) with caution (abuse potential).
  • Clozapine for refractory tremor (risk of agranulocytosis).
  • Memantine and pramipexole show some benefit in small studies.
  • Ineffective: levetiracetam, 3,4-diaminopyridine.
  • Alcohol may temporarily improve tremor but not recommended long-term.

OTHER THERAPIES

  • Botulinum toxin A: recommended for cervical dystonia; may help blepharospasm, focal tremors.

SURGERY/OTHER PROCEDURES

  • Deep brain stimulation (DBS) of thalamic ventral intermediate nucleus: most effective for refractory cases.
  • Unilateral thalamotomy possible; bilateral thalamotomy not recommended.
  • Emerging interest in external neuromodulation devices.

COMPLEMENTARY & ALTERNATIVE MEDICINE

  • Physical therapy for strengthening and adaptive training (e.g., weighted utensils).
  • No evidence for improved functional ability from strength training alone.

ONGOING CARE

DIET

  • Avoid caffeine.

PATIENT EDUCATION

  • Essential tremor does not reduce life expectancy but may worsen over time.

PROGNOSIS

  • Tremor amplitude tends to increase with age.

REFERENCES

  1. Zesiewicz TA, Elble RJ, Louis ED, et al. Evidence-based guideline update: treatment of essential tremor: report of the Quality Standards Subcommittee of the American Academy of Neurology. Neurology. 2011;77(19):1752-1755.
  2. Handforth A, Bordelon Y, Frucht SJ, et al. A pilot efficacy and tolerability trial of memantine for essential tremor. Clin Neuropharmacol. 2010;33(5):223-226.
  3. Herceg M, Nagy F, Pál E, et al. Pramipexole may be an effective treatment option in essential tremor. Clin Neuropharmacol. 2012;35(2):73-76.

CODES

  • ICD10 G25.0 Essential tremor

CLINICAL PEARLS

  • Diagnosis requires bilateral action/postural tremor ≥3 years without resting component.
  • Alcohol responsiveness and family history aid differentiation from Parkinson disease.
  • Rule out Wilson disease, thyroid dysfunction, medication effects.
  • Brain MRI usually unnecessary.
  • Propranolol and primidone are first-line agents, though 30-50% may not respond.