In an adult with a postural tremor without an obvious acute cause, what are the likely etiologies, appropriate diagnostic work‑up, and first‑line treatment options?

Postural Tremors: Etiologies, Diagnostic Approach, and First-Line Treatment

Most Likely Etiologies

Essential tremor is the most common pathologic cause of postural tremor in adults, affecting 0.4–6% of the population, and typically presents as a bilateral, symmetric action tremor of 4–8 Hz frequency involving the upper extremities and sometimes the head. 1, 2

Primary Differential Diagnoses

• Essential tremor accounts for the majority of postural tremors and manifests as both postural and kinetic tremor without latency, often with family history (autosomal dominant in 50% of cases) and characteristic improvement with alcohol 1, 2, 3

• Enhanced physiologic tremor appears as low-amplitude, high-frequency tremor exacerbated by anxiety, caffeine, fatigue, medications (beta-agonists, valproate, lithium, corticosteroids), or metabolic disturbances (hyperthyroidism, hypoglycemia) 2, 3

• Parkinson's disease re-emergent tremor presents as postural tremor that emerges after a latency of several seconds to minutes when holding a posture, typically 3–5 Hz, and may occur with or without observable rest tremor 4

• Drug-induced tremor from medications including antipsychotics, antidepressants, anticonvulsants, and immunosuppressants should be considered in any patient with new-onset tremor 2

• Cerebellar tremor manifests as intention tremor during goal-directed movement but may have a postural component, often accompanied by ataxia, dysmetria, or other cerebellar signs 5, 2

• Dystonic tremor occurs in the context of dystonic posturing and is typically irregular, task-specific, and may have a null point where tremor disappears 2

Critical Distinguishing Features

The key to diagnosis is determining whether the tremor occurs at rest, with maintained posture, or during movement, and whether there is latency before tremor onset. 4, 2

• Rest tremor (present when limb is completely supported and relaxed) strongly suggests Parkinson's disease and responds to dopaminergic therapy 4, 5

• Postural tremor without latency that persists during movement suggests essential tremor or enhanced physiologic tremor 4, 2

• Postural tremor with 2–4 second latency (re-emergent tremor) indicates Parkinson's disease, even without obvious rest tremor 4

• Intention tremor (worsening as target is approached) indicates cerebellar pathology 5, 2

Diagnostic Work-Up

Essential History Elements

• Onset and progression: Essential tremor typically starts in adulthood and progresses slowly with age, while abrupt onset suggests psychogenic or drug-induced etiology 1, 2

• Family history: Autosomal dominant inheritance in 50% of essential tremor cases 1

• Alcohol response: Improvement with ethanol is characteristic of essential tremor 1, 3

• Medication review: Systematically review all medications, as drug-induced tremor is a common and reversible cause 2

• Associated symptoms: Bradykinesia, rigidity, or postural instability suggest Parkinson's disease; ataxia or dysmetria suggest cerebellar disease 2

Physical Examination Maneuvers

Observe tremor in three positions: complete rest with limb fully supported, arms outstretched in front (postural), and during finger-to-nose testing (kinetic/intention). 2, 3

• Rest tremor assessment: Have patient sit with hands resting in lap, completely relaxed and supported; Parkinson's tremor appears within seconds 4, 5

• Re-emergent tremor test: Have patient hold arms outstretched and observe for tremor that emerges after 5–10 seconds of latency, which indicates Parkinson's disease 4

• Postural tremor: Arms extended forward at shoulder height; essential tremor appears immediately without latency 4, 2

• Kinetic tremor: Finger-to-nose testing; worsening amplitude approaching target indicates cerebellar pathology 2

• Distraction test: Psychogenic tremor characteristically diminishes or changes character with distraction (e.g., serial 7s, alternate hand movements) 2

Laboratory and Imaging

Routine laboratory testing and neuroimaging are not indicated for typical essential tremor or enhanced physiologic tremor. 2

• Thyroid function tests (TSH, free T4) should be obtained in all patients with new postural tremor to exclude hyperthyroidism 2

• Basic metabolic panel to assess for electrolyte disturbances, renal dysfunction, or hypoglycemia if clinically indicated 2

• Ceruloplasmin and 24-hour urine copper in patients under age 40 with tremor plus psychiatric symptoms, liver disease, or Kayser-Fleischer rings to exclude Wilson's disease 2, 3

• Brain MRI is indicated only when atypical features are present: asymmetric tremor, rapid progression, associated neurological signs (ataxia, dystonia, cognitive decline), or age of onset under 40 years 2

• DaTscan (single-photon emission computed tomography) can differentiate Parkinson's disease from essential tremor when diagnostic uncertainty persists after clinical evaluation, showing reduced dopaminergic pathway integrity in Parkinson's disease 2

First-Line Treatment Options

Essential Tremor

Propranolol (40–320 mg daily in divided doses) and primidone (starting 12.5–25 mg at bedtime, titrating to 250 mg daily) are the only FDA-supported first-line medications for essential tremor, with approximately 50–70% of patients achieving meaningful tremor reduction. 6, 1, 3

• Propranolol is contraindicated in asthma, chronic obstructive pulmonary disease, heart block, and uncontrolled heart failure; start 20 mg twice daily and titrate to effect 6, 1

• Primidone causes acute sedation and ataxia in up to 30% of patients when started at standard doses; begin with 12.5–25 mg at bedtime and increase by 25 mg every week to minimize side effects 1, 3

• At least 30% of patients have insufficient relief from first-line medications, and second-line agents (gabapentin, topiramate) are less effective 6, 1

• Deep brain stimulation of the ventral intermediate nucleus of the thalamus is indicated for medication-refractory essential tremor causing significant functional disability 6

Enhanced Physiologic Tremor

Identify and eliminate the underlying cause: discontinue offending medications, treat hyperthyroidism, reduce caffeine intake, and address anxiety. 2, 3

• Propranolol 10–40 mg as needed before situations requiring fine motor control (public speaking, performances) can provide symptomatic relief 3

Parkinson's Disease Tremor

Carbidopa-levodopa (starting 25/100 mg three times daily) is first-line for parkinsonian tremor, though tremor is often the least responsive motor symptom to dopaminergic therapy. 4, 5, 3

• Anticholinergics (trihexyphenidyl 1–2 mg three times daily) may be added for tremor-dominant Parkinson's disease in younger patients without cognitive impairment 5, 3

• Re-emergent postural tremor responds to the same dopaminergic therapy as rest tremor, sharing the same 3–5 Hz frequency and pathophysiology 4

Common Diagnostic Pitfalls

• Misdiagnosing Parkinson's disease re-emergent tremor as essential tremor because the postural component is more prominent than rest tremor; always observe for latency of several seconds before tremor onset 4

• Assuming all postural tremors are essential tremor without considering enhanced physiologic tremor from medications, caffeine, or metabolic causes, which are reversible 2

• Failing to recognize that 30% of essential tremor patients develop head tremor, which can help distinguish it from Parkinson's disease (head tremor is rare in Parkinson's) 1

• Overlooking coexistent essential tremor and Parkinson's disease, which occurs in some patients and manifests as postural tremor without latency superimposed on re-emergent tremor 4

• Relying on patient description alone rather than direct observation of tremor in multiple positions (rest, posture, movement) to determine activation pattern 2, 3