What are the possible causes of a tremor that mimics Parkinson's disease?

Causes of Parkinsonian-Like Tremor

Multiple conditions can produce tremor that mimics Parkinson's disease, with essential tremor being the most common mimic, but critical distinctions exist in tremor characteristics, associated symptoms, and underlying pathophysiology that guide diagnosis.

Primary Tremor Disorders

Essential Tremor

• Essential tremor manifests primarily as postural and kinetic tremor (occurring with movement and maintaining posture), rarely involves the chin or jaw, and predominantly affects hands, head, and voice 1
• Unlike Parkinson's disease, essential tremor does not occur at rest and lacks the characteristic "pill-rolling" quality 2, 1
• Essential tremor patients typically lack bradykinesia, rigidity, and postural instability that define parkinsonian syndromes 1

Parkinsonian Tremor (True Parkinson's Disease)

• Resting tremor is the most distinctive feature, appearing when the limb is at rest and diminishing with voluntary movement 2
• Tremor typically begins unilaterally in the hands with a characteristic "pill-rolling" quality 2
• Must be accompanied by bradykinesia (slowness of movement) for Parkinson's disease diagnosis, often with rigidity and postural instability 1

Secondary Causes of Parkinsonian-Like Tremor

Drug-Induced Parkinsonism

• Medications can produce tremor and parkinsonian features that mimic Parkinson's disease 3
• This represents a reversible cause that must be excluded

Atypical Parkinsonian Syndromes

• Multiple system atrophy, progressive supranuclear palsy, and corticobasal degeneration can present with tremor and parkinsonian features 3
• These conditions typically have additional distinguishing neurological signs

Metabolic and Structural Causes

• Hyperthyroidism can produce tremor and must be excluded with thyroid function testing 4
• Calcium-phosphate metabolism disorders (hypoparathyroidism, pseudoparathyroidism) and basal ganglia calcification can cause secondary parkinsonism 4
• Cerebrovascular disease and demyelinating diseases (especially multiple sclerosis) can produce parkinsonian tremor 4

Wilson's Disease

• Can present with tremor and parkinsonian features, particularly in younger patients 3
• Requires serum ceruloplasmin testing for diagnosis 4

Fragile X-Associated Tremor/Ataxia Syndrome

• Can present with prominent tremor and parkinsonian features 3
• Typically occurs in older male carriers of fragile X premutation

Paroxysmal Movement Disorders That May Mimic Tremor

Paroxysmal Kinesigenic Dyskinesia

• Presents with brief episodes (less than 1 minute) of dystonia, chorea, or ballism triggered by sudden movement 4
• Consciousness is preserved during attacks, distinguishing it from seizures 4
• Responds well to low-dose carbamazepine or oxcarbazepine 4

Epilepsy (Frontal Lobe)

• Can present with stereotypic chorea and dystonia that may be confused with tremor 4
• Unlike parkinsonian tremor, seizures can occur during sleep and may have altered consciousness 4

Vestibular Disorders (Not True Tremor)

Vestibular Migraine

• Presents with episodic vertigo lasting hours, sometimes with visual symptoms 4
• May be misinterpreted as tremor-related imbalance but lacks true tremor 4

Ménière's Disease

• Causes episodic vertigo with hearing loss, tinnitus, and aural fullness 4
• The imbalance may be confused with parkinsonian postural instability but lacks tremor 4

Diagnostic Approach

Key Clinical Distinctions

• Determine tremor timing: Rest tremor suggests Parkinson's disease; postural/kinetic tremor suggests essential tremor 2, 1
• Assess for bradykinesia and rigidity: Required for Parkinson's disease diagnosis 1
• Note tremor distribution: Unilateral onset with "pill-rolling" suggests Parkinson's disease; bilateral hand/head/voice tremor suggests essential tremor 2, 1

Definitive Testing

• DaTscan (Ioflupane SPECT/CT) is the most useful imaging test to differentiate parkinsonian syndromes from essential tremor, showing reduced dopamine transporter binding in Parkinson's disease and normal binding in essential tremor 1
• Thyroid function, calcium/phosphorus levels, ceruloplasmin, and brain MRI should be obtained to exclude secondary causes 4

Treatment Implications

For Parkinsonian Tremor

• Levodopa/carbidopa is first-line treatment for parkinsonian tremor, with dopamine agonists as alternatives 1
• Deep brain stimulation of VIM thalamus can be used for medication-refractory cases 1

For Essential Tremor

• Propranolol or primidone are first-line medications, effective in up to 70% of patients 1
• MRI-guided focused ultrasound thalamotomy shows 56% tremor improvement sustained at 4 years for refractory cases 1

Critical Pitfalls to Avoid

• Do not diagnose Parkinson's disease based on tremor alone—bradykinesia must be present 1
• Do not assume all elderly patients with tremor have Parkinson's disease—essential tremor is more common 1
• Do not overlook medication history—drug-induced parkinsonism is reversible 3
• Do not skip metabolic screening—thyroid disorders and Wilson's disease are treatable causes 4