What is the cause and management of a left arm tremor in an adult when reaching for objects?

Action Tremor in the Left Arm: Diagnosis and Management

This is most likely essential tremor, and you should initiate treatment with propranolol (80-240 mg/day) or primidone as first-line therapy if the tremor interferes with function or quality of life. 1, 2

Immediate Diagnostic Priorities

The critical first step is determining when the tremor occurs—this single observation dramatically narrows your differential 3:

• Action/kinetic tremor (occurs when reaching for objects): Most commonly essential tremor, enhanced physiological tremor, or cerebellar pathology 3, 4
• Rest tremor (improves with voluntary movement): Parkinson's disease 3
• Postural tremor (occurs with maintained posture): Essential tremor or enhanced physiological tremor 4, 5

Since this tremor occurs when reaching for an object, this is an action/kinetic tremor, making essential tremor the most likely diagnosis 4, 5.

Rule Out Life-Threatening and Reversible Causes First

Before diagnosing essential tremor, you must exclude these conditions:

Drug-Induced Tremor

• Check medication list immediately—this is common and reversible 3
• Sympathomimetics (cocaine, amphetamines, decongestants) cause fine tremor with tachycardia and sweating 6, 3
• Antipsychotics, lithium, valproate, and SSRIs are common culprits 3
• Management: Withdraw the suspected agent and observe for response 6

Hyperthyroidism

• Look for fine tremor of outstretched hands with warm, moist skin, heat intolerance, weight loss 6, 3
• Screen with TSH and free T4 6, 3

Cerebellar Pathology

• Produces coarse, irregular "wing-beating" tremor during finger-to-nose testing 3
• Associated with dysarthria and ataxic gait 3
• Red flag: If present, obtain brain MRI immediately 6

Functional (Psychogenic) Tremor

• Key diagnostic feature: Distractibility—tremor stops when attention is redirected to another task 3
• Variable frequency and amplitude are characteristic 3
• Do not miss this—it wastes resources if not identified early 3

Essential Tremor: Definitive Diagnosis

Essential tremor is characterized by 4, 5:

• Postural and kinetic tremor with frequency between 4-8 Hz 4
• Involves mainly upper extremities and head 4
• Progressive neurologic disorder that can cause substantial disability 7
• Affects 5-10 million persons in the United States 7

First-Line Pharmacological Treatment

Initiate treatment only when tremor interferes with function or quality of life 1, 2:

Propranolol (Preferred First-Line)

• Dose: 80-240 mg/day 1
• Effective in up to 70% of patients 1, 2
• Most established medication for essential tremor, used for over 40 years 1
• Produces mean tremor reduction of about 50% 8

Critical contraindications to propranolol 1, 2:

• Chronic obstructive pulmonary disease or asthma (risk of bronchospasm) 1, 2
• Bradycardia (<50 bpm) 1
• Decompensated heart failure 1
• Second- or third-degree heart block 1

Common adverse effects 1:

• Fatigue, depression, nausea, dizziness, insomnia 1
• Dizziness and hypotension (particularly concerning if patient has gait instability) 2
• In elderly patients, excessive heart rate reduction may lead to serious adverse events 1

Primidone (Equally Effective First-Line Alternative)

• Start low and titrate slowly—therapeutic benefit can occur even when derived phenobarbital levels remain subtherapeutic 1, 2
• Clinical benefits may not become apparent for 2-3 months—an adequate trial period is essential 1, 2
• Does not require routine dose adjustment for impaired renal function 2

Important warnings 1:

• Behavioral disturbances, irritability, and sleep disturbances can occur at higher doses 1
• Women of childbearing age require counseling about teratogenic risks (neural tube defects) 1, 2

Combination Therapy

• If either propranolol or primidone alone do not provide adequate control, use them in combination 9, 7

Second-Line Medications

If first-line agents fail or are contraindicated 9, 7:

• Benzodiazepines (clonazepam) may provide benefit 9, 7
• Gabapentin has limited evidence for moderate efficacy 1, 9
• Topiramate may be helpful 9, 7

Surgical Options for Medication-Refractory Tremor

Consider surgical intervention when medications fail due to lack of efficacy at maximum doses, dose-limiting side effects, or medical contraindications 1, 2:

Magnetic Resonance-Guided Focused Ultrasound (MRgFUS) Thalamotomy

• Preferred for unilateral tremor 1, 2
• Shows sustained tremor improvement of 56% at 4 years 1, 2
• Lower complication rate (4.4%) compared to radiofrequency thalamotomy (11.8%) and DBS (21.1%) 1, 2
• Early adverse effects include gait disturbance (36%) and paresthesias (38%), which decrease to 9% and 14% respectively by 1 year 1

Contraindications to MRgFUS 1, 2:

• Cannot undergo MRI 1
• Skull density ratio <0.40 1
• Bilateral treatment needed 1
• Contralateral to previous thalamotomy 1

Deep Brain Stimulation (DBS)

• Reduces tremor by about 90% 8
• Preferred for bilateral tremor involvement 1
• Provides adjustable, reversible tremor control that can be optimized over time 1
• Higher complication rate (21.1%) than MRgFUS 1

Critical Pitfalls to Avoid

• Do not miss drug-induced tremor—always check the medication list first 3
• Do not overlook hyperthyroidism—screen with TSH and free T4 6, 3
• Test for distractibility—functional tremor wastes resources if not identified early 3
• Avoid propranolol in patients with asthma, COPD, or decompensated heart failure 1, 2
• Give primidone an adequate 2-3 month trial before declaring treatment failure 1, 2
• Counsel women of childbearing age about teratogenic risks with primidone 1, 2

Monitoring and Follow-Up

• Regular assessment of tremor severity and medication side effects is essential 1, 2
• Dose adjustments based on clinical response and tolerability 1, 2
• If first-line agents fail, switch to or add second-line medications before considering surgical options 1