What differentiates essential tremor from intentional tremor in terms of characteristics and treatment?

Differentiating Essential Tremor from Intentional Tremor: Characteristics and Treatment

Essential tremor and intentional tremor are distinct tremor types with different characteristics, etiologies, and treatment approaches, with intentional tremor typically indicating cerebellar pathology while essential tremor is a progressive neurological syndrome that may develop intentional components over time. 1, 2

Characteristics and Differentiation

Essential Tremor

• Most common movement disorder apart from restless leg syndrome, with prevalence in the US between 0.3% and 5.55% 3
• Primarily presents as bilateral action tremor of the arms and hands that has been present for at least 3 years 4
• Progressive and disabling, significantly interfering with quality of life, functional activities, mood, and socialization 3
• Can cause greater impairment than Parkinson's disease in activities like writing, eating, drinking, and reading 3
• May develop an intentional component in approximately 25% of patients (termed "essential tremor plus" or "intention ET") 2
• Patients with intention ET tend to be older and more often show head and trunk involvement 2

Intentional Tremor

• Characterized by coarse, irregular tremor that becomes more pronounced during goal-directed movements 1
• Often has a "wing-beating" appearance, particularly evident during finger-to-nose testing 1
• Frequently accompanied by dysarthria (slurred speech) and ataxic gait 1
• Primarily associated with cerebellar pathology or its connections 1, 2
• Common etiologies include:
  • Multiple sclerosis with demyelinating lesions in cerebellar pathways 1
  • Wilson's disease 1
  • Traumatic brain injury affecting the cerebellum 1
  • Medication side effects 1
  • Toxic exposures affecting cerebellar function 1

Key Differentiating Features

• Intentional tremor worsens as the limb approaches a target, while essential tremor is primarily postural and kinetic 2
• Neurophysiological studies show that patients with intention ET have:
  • Lower thalamic neuronal firing rates 5
  • Lower spike×EMG coherence 5
  • Lower spike×EMG phase lead compared to those with postural ET 5
• Quantitative analysis shows intention tremor has increased amplitude of curvature during deceleration and target phase of movement 2
• Hypermetria is significantly increased in patients with intentional tremor components 2

Treatment Approaches

Essential Tremor Treatment

• First-line pharmacological treatment includes:
  • Propranolol (80-240 mg/day) - most established medication with over 40 years of demonstrated efficacy 6
  • Primidone - another first-line option effective in up to 70% of patients 6
• Treatment should only be initiated when tremor interferes with function or quality of life 3, 6
• Second-line medications include gabapentin and carbamazepine, though they're generally less effective 6

Intentional Tremor Treatment

• More challenging to treat pharmacologically than essential tremor 1
• May respond to:
  • Isoniazid 7
  • Clonazepam 7
  • Topiramate 7
• Physical therapy and occupational therapy with adaptive devices may help improve function 7

Surgical Options for Refractory Cases

• For medically refractory tremor causing significant disability, consider:
  • Magnetic resonance-guided focused ultrasound (MRgFUS) thalamotomy - shows sustained tremor improvement of 56% at 2 years 3
  • Deep brain stimulation (DBS) - particularly effective for intention tremor components 6
  • Radiofrequency thalamotomy 6

Surgical Considerations

• MRgFUS thalamotomy has a lower complication rate (4.4%) compared to radiofrequency thalamotomy (11.8%) and DBS (21.1%) 3
• MRgFUS is contraindicated in patients who:
  • Cannot undergo MRI 3
  • Have skull density ratio <0.40 3
  • Need bilateral treatment or have previous contralateral thalamotomy 3

Clinical Pearls and Pitfalls

• Essential tremor is increasingly recognized as a heterogeneous syndrome that extends beyond tremor to involve disturbances in gait, speech, cognition, and mood 4
• Intention tremor components in essential tremor suggest cerebellar involvement and may indicate more advanced disease 2
• Beta-blockers should be avoided in patients with chronic obstructive pulmonary disease, bradycardia, or congestive heart failure 6
• For patients with both essential tremor and hypertension, beta-blockers may provide dual benefits 6
• Treatment selection should be based on tremor severity, functional disability, impact on social interactions, and patient preferences 4