What are the medical causes of physiological tremor?

Medical Causes of Physiological Tremor

Physiological tremor has multiple medical causes including hyperthyroidism, drug/alcohol use, anxiety, and various neurological conditions, with treatment directed at the underlying cause.

Definition and Characteristics

Physiological tremor is an involuntary rhythmic oscillation of a body part produced by reciprocally innervated antagonist muscles 1. While everyone has a baseline physiological tremor that is typically asymptomatic, certain medical conditions can accentuate this tremor to the point where it becomes noticeable and potentially disabling.

Common Medical Causes

Endocrine Disorders

• Hyperthyroidism: One of the most common endocrine causes, characterized by warm moist skin, heat intolerance, nervousness, tremulousness, insomnia, weight loss, and proximal muscle weakness 2. The tremor typically presents as a fine tremor of the outstretched hands.
• Hyperparathyroidism: Can cause tremor, though less commonly than hyperthyroidism 2.

Drug and Substance-Related Causes

• Medications: Many medications can induce or exacerbate tremor, including:

  • Sympathomimetics (decongestants, anorectics)
  • Antipsychotics
  • Selective serotonin/norepinephrine reuptake inhibitors (SSRIs/SNRIs)
  • Lithium
  • Valproate
  • Amiodarone
  • Beta-adrenoceptor agonists 3

• Substances:

  • Caffeine
  • Nicotine
  • Alcohol (both intoxication and withdrawal)
  • Cocaine, amphetamines, and other illicit drugs 2

Neurological Conditions

• Essential Tremor: The most common pathologic tremor, presenting as postural and kinetic tremor with a frequency between 4-8 Hz, primarily affecting upper extremities and head 4.
• Parkinson's Disease: Causes a 4-6 Hz resting tremor typically in the arms and legs 4.
• Wilson's Disease: A rare genetic disorder of copper metabolism that can present with tremor.
• Cerebellar Lesions: Damage to the cerebellum can result in intention tremor.

Metabolic Disorders

• Hypoglycemia: Can cause tremor as part of the sympathetic response to low blood sugar.
• Vitamin B12 Deficiency: May present with neurological symptoms including tremor.
• Uremia: Advanced kidney disease can cause metabolic tremor.

Psychological Factors

• Anxiety and Stress: Strong association between anxiety disorders, post-traumatic stress disorder (PTSD), and tremor 5.
• Depression: Often comorbid with tremor disorders 5.

Less Common Causes

• Pheochromocytoma/Paraganglioma: Rare catecholamine-secreting tumors that can cause episodic hypertension, headache, sweating, palpitations, and tremor 2.
• Cushing's Syndrome: Excess cortisol can sometimes present with tremor among other symptoms 2.
• Multiple Sclerosis: Demyelinating lesions can cause various movement disorders including tremor.
• Stroke: Particularly those affecting the cerebellum or basal ganglia pathways.

Diagnostic Approach

When evaluating physiological tremor:

1. Characterize the tremor:

   • Position-dependent (rest, postural, kinetic)
   • Frequency and amplitude
   • Distribution (which body parts are affected)
   • Symmetry or asymmetry

2. Look for associated symptoms:

   • Tachycardia, sweating (suggesting sympathetic activation)
   • Weight changes, heat/cold intolerance (suggesting thyroid disease)
   • Neurological deficits (suggesting central nervous system pathology)

3. Medication review:

   • Complete review of all medications, including over-the-counter and supplements
   • Timing relationship between medication initiation and tremor onset

4. Laboratory testing based on clinical suspicion:

   • Thyroid function tests
   • Serum calcium and parathyroid hormone levels
   • Liver and kidney function tests
   • Drug screens when appropriate

Management

Treatment should target the underlying cause:

• Hyperthyroidism: Anti-thyroid medications, radioactive iodine, or surgery 2.
• Drug-induced tremor: Discontinuation of the offending agent when possible 3.
• Essential tremor: Beta-blockers (particularly propranolol) and primidone are first-line treatments 4, 6. Propranolol is specifically FDA-approved for essential tremor 7.
• Parkinsonian tremor: Anticholinergics and levodopa/carbidopa 6.
• Anxiety-related tremor: Treatment of the underlying anxiety disorder and potentially beta-blockers for symptomatic relief.

Clinical Pearls and Pitfalls

• Physiological tremor worsens with anxiety, fatigue, and caffeine consumption.
• Multiple medications can cause or exacerbate tremor; always consider a medication review.
• Tremor that persists during sleep suggests a different diagnosis (e.g., seizure disorder).
• Beta-blockers can mask symptoms of hypoglycemia, so use with caution in diabetic patients.
• Unilateral tremor, sudden onset, or tremor with other neurological signs warrants neuroimaging to rule out structural lesions.
• Alcohol temporarily improves essential tremor but can lead to rebound worsening when it wears off.

Remember that physiological tremor exists on a spectrum, and the goal of treatment is to identify and address the underlying cause while providing symptomatic relief when necessary.