What are the most common causes of tremor?

Most Common Causes of Tremor

Essential tremor and Parkinson's disease are the most common causes of tremor, followed by drug-induced tremor, physiologic tremor, and various neurological disorders including cerebellar disorders and dystonia. 1

Classification of Tremors

Tremors can be categorized based on when they occur:

1. Resting tremor:

   • Occurs when the body part is at rest
   • Most commonly seen in Parkinson's disease (4-6 Hz)
   • Typically affects arms and legs 2

2. Postural tremor:

   • Occurs when maintaining a position against gravity
   • Characteristic of essential tremor (4-8 Hz)
   • Primarily affects upper extremities and head 2

3. Kinetic/Action tremor:

   • Occurs during voluntary movement
   • Often seen in cerebellar disorders
   • Can worsen as the patient approaches a target (intention tremor) 1

Common Causes of Tremor

1. Essential Tremor

• Most common tremor disorder 3
• Characterized by postural and kinetic tremor (4-8 Hz)
• Primarily affects upper extremities and head
• Often has familial pattern
• Typically worsens with stress and improves with alcohol 2

2. Parkinson's Disease

• Most common cause of resting tremor
• Due to dopaminergic neuron loss in the substantia nigra
• Typically asymmetric at onset
• Associated with bradykinesia and rigidity 1

3. Drug-Induced Tremor

• Common medications causing tremor include:
  • Antidepressants (SSRIs/SNRIs)
  • Mood stabilizers (lithium, valproate)
  • Cardiac medications (amiodarone)
  • Bronchodilators (β-adrenoceptor agonists)
  • Antipsychotics
  • Stimulants 4
• Risk factors include polypharmacy, male gender, older age, and high doses 4

4. Physiologic Tremor

• Normal phenomenon exacerbated by:
  • Anxiety/stress
  • Caffeine
  • Fatigue
  • Hypoglycemia
  • Hyperthyroidism 1

5. Neurological Disorders

• Multiple systems atrophy
• Progressive supranuclear palsy
• Cerebellar disorders
• Wilson's disease (copper metabolism disorder)
• Multiple sclerosis 1, 5

6. Metabolic Causes

• Hepatic encephalopathy (asterixis or "flapping tremor")
• Thyroid dysfunction
• Electrolyte disturbances 1

7. Other Causes

• Dystonic tremor
• Psychogenic/functional tremor
• Orthostatic tremor (occurs when standing)
• Neuropathic tremor (associated with peripheral neuropathies)
• Alcohol withdrawal 3

Clinical Pearls and Pitfalls

• Diagnostic pitfall: Mistaking enhanced physiologic tremor for essential tremor or Parkinson's disease
• Important consideration: Always check medication list when evaluating tremor
• Caveat: Wilson's disease, though rare, is an important treatable cause of tremor in young patients and should not be missed
• Remember: Tremor that appears suddenly, is distractible, or shows entrainment may suggest functional (psychogenic) tremor 4
• Note: Some tremors (like those in hepatic encephalopathy) may not be fully reversible after repeated episodes 1

Diagnostic Approach

When evaluating tremor, consider:

• Timing (rest, postural, kinetic)
• Distribution (which body parts are affected)
• Frequency and amplitude
• Exacerbating and relieving factors
• Associated neurological symptoms
• Medication history
• Family history

Relevant diagnostic tests may include:

• Thyroid function tests
• Liver function tests
• Serum ceruloplasmin (for Wilson's disease)
• Glucose levels
• Calcium-phosphorus metabolism 1

Neuroimaging with MRI may be indicated to evaluate for structural causes, particularly when tremor is accompanied by other neurological signs 1.