Essential Tremor & Deep Brain Stimulation (DBS)

What is essential tremor?

The most common pathological tremor.

Essential tremor (ET) is a chronic neurological disorder that causes shaking during movement or when holding an object steady, most commonly in the hands. It is not simply “nervousness,” nor is it the same as Parkinson’s disease, although the two are often confused.

For many individuals the tremor is mild. For others, however, it progresses to a level that significantly interferes with eating, writing, self-care, and professional life.

How common is it and at what ages does it occur?

More prevalent than Parkinson’s, Huntington’s, or Alzheimer’s disease.

Essential tremor is among the most common neurological conditions:

• it affects approximately 1–5% of the general population
• the true prevalence is likely higher, as many individuals do not seek medical care
• its frequency increases markedly after 60 years of age
• there is also a second peak in young adulthood, with about 5% of new diagnoses occurring in individuals under 20 years
• men and women are affected at similar rates
• essential tremor does not reduce life expectancy, but it can significantly impair quality of life.

What are the main symptoms?

Where tremor appears and how its severity is assessed.

Essential tremor is typically:

• action tremor, occurring during voluntary movement
• postural tremor, when holding an object steady or keeping the arms extended
• with a frequency of approximately 4–12 Hz.

Typical pattern:

• often begins mildly, frequently in one hand
• gradually becomes bilateral
• the frequency may decrease, while the amplitude of movement increases.

Statistically:

• 90% of patients—tremor of the hands
• 50%—tremor of the head
• 30%—tremor of the voice
• 15%—tremor of the legs.

Over time, patients may experience:

• difficulty with handwriting
• difficulty with fine motor tasks (jewelry, buttons, work tools)
• mild gait, targeting, and movement changes related to cerebellar dysfunction.

Objective assessment of severity commonly uses scales such as the Fahn–Tolosa–Marin (FTM) rating. Stages 3 and 4 are associated with significant impairment in essential daily activities (writing, eating, dressing, hygiene).

Many patients notice that a small amount of alcohol temporarily reduces tremor frequency and severity; however, this is not a treatment and is certainly not a safe long-term strategy.

Why does it occur—what do we know about the cause?

Familial (hereditary) and sporadic forms of essential tremor.

The exact cause of essential tremor is not fully understood, but we know that:

• 50–70% of cases are familial, often with an autosomal dominant inheritance pattern—meaning that a single affected gene from one parent can be sufficient to cause the condition.
• Possible genetic loci (e.g., on chromosomes 2p and 3q) have been identified in certain families.
• Sporadic (non-familial) forms, particularly after age 40, have been associated with exposure to alkaloids found in tobacco and certain plant products.
• PET and fMRI studies primarily demonstrate cerebellar dysfunction, with additional involvement of the brainstem, thalamus, and inferior olive.

How is it diagnosed and distinguished from Parkinson’s disease?

A clinical diagnosis with careful exclusion of other causes of tremor.

Diagnosis is based on:

• detailed history (onset, progression, family history)
• neurological examination—symmetric, bilateral action/postural tremor of the hands, ± head tremor without dystonia or abnormal posturing
• absence of other neurological signs (rigidity, bradykinesia, marked instability, significant cognitive decline).

According to Movement Disorder Society criteria, diagnosis requires:

• bilateral, symmetric action/postural tremor of the hands
• possible head tremor without dystonia
• no alternative explanation (medications, Parkinson’s disease, Wilson’s disease, Huntington’s disease, etc.).

Differential diagnosis includes:

• Physiologic tremor (fatigue, anxiety, caffeine, hypoglycemia).
• Primary orthostatic tremor—mainly affecting the legs, appearing on standing and resolving with movement or sitting.
• Parkinson’s disease—rest tremor (3–5 Hz), associated with rigidity, bradykinesia, and postural instability, and not improved by alcohol.
• Wilson’s disease—young patients with tremor, Kayser–Fleischer rings, liver disease, and psychiatric symptoms.
• Huntington’s disease—chorea, cognitive decline, and typically a mid-life family history.

When differentiation from Parkinson’s disease is uncertain, DaT–SPECT (DaTscan) may be used: dopaminergic pathways are reduced in Parkinson’s, while they are usually normal in essential tremor.

When is treatment necessary?

We treat the person, not just the number on a rating scale.

Surgical therapy is not indicated for every mild form of essential tremor. We usually consider interventional treatment when:

• tremor interferes with daily activities
• symptoms lead to avoidance of social situations
• tremor creates functional or safety risks

Mild tremor occurring only with stress, fatigue, or caffeine may simply be monitored, along with lifestyle modification.

What are the medical treatment options?

First-line: propranolol or primidone—followed by individualized therapy.

First-line medications:

• Propranolol (β-blocker, 20–320 mg/day): reduces tremor amplitude by approximately 50%. Use with caution in asthma, hypotension, and bradycardia.
• Primidone (antiepileptic, 25–300 mg/day): reduces tremor by ~40–50%. Requires careful titration due to sedation or dizziness at higher doses.

Secondary or adjunctive options:

• Low-dose benzodiazepines (e.g., for significant anxiety)
• Atypical neuroleptics in selected cases
• Botulinum toxin (Botox) for focal tremor (e.g., head or voice), to reduce excessive contraction of specific muscles.

As the condition progresses, declining medication efficacy is common, often necessitating higher doses with increased side effects.

When is tremor considered “medication-refractory”?

The point at which medication is no longer sufficient for a normal daily life.

Medication-refractory essential tremor is defined when:

• at least two appropriate medication regimens (e.g., propranolol, primidone, ± others when indicated) have been tried at adequate doses and duration
• and the patient continues to experience severe tremor (FTM 3–4) with significant impact on eating, writing, self-care, and work.

At this stage, further medication escalation usually yields limited additional benefit and more side effects. For these patients, interventional therapy is considered.

What surgical options exist (DBS, thalamotomy, MRgFUS)?

Different tools for different patient profiles.

The main interventional options for severe, medication-refractory essential tremor are:

• Deep Brain Stimulation (DBS) of the VIM thalamus
  Implantation of electrodes in the VIM nucleus of the thalamus connected to an implantable pulse generator.
  ✔ Adjustable, reversible, and supported by extensive worldwide experience.
• Stereotactic radiofrequency thalamotomy
  Creation of a small focal lesion in the VIM nucleus (classic thalamotomy). Now used less frequently due to higher risk of permanent complications, particularly when performed bilaterally.
• Gamma Knife thalamotomy
  Radiosurgical lesioning of the VIM without craniotomy, but with delayed onset of effect and limited predictability of lesion size.
• MR-guided Focused Ultrasound (MRgFUS)
  Non-invasive thermal lesioning of the VIM under real-time MRI guidance. Provides immediate effect, but the lesion is irreversible and currently applied unilaterally in selected centers and cases.

The choice of method depends on:

• age and overall medical condition
• severity and distribution of tremor (unilateral vs bilateral)
• comorbidities and contraindications
• personal preference regarding reversible versus permanent intervention.

What is thalamic (VIM) deep brain stimulation and how is it performed?

High-precision stereotactic targeting of the thalamus.

DBS for essential tremor targets the VIM nucleus of the thalamus, which plays a key role in transmitting cerebellar signals. The procedure is performed in two stages:

1. Electrode placement
   – High-resolution preoperative MRI
   – On the day of surgery: conscious sedation and intraoperative CT
   – CT–MRI fusion in a neuronavigation system
   – Trajectory planning to avoid critical brain structures.
2. Stereotactic approach & targeting
   – Microelectrode recording (MER) is used to identify the characteristic “kinesthetic” neurons of the VIM.
3. Test stimulation
   – Low-current stimulation (1–5 μA) produces characteristic contralateral paresthesias
   – We assess tremor reduction and the stimulation threshold at which side effects occur (paresthesia, muscle contraction, dysarthria)
   – The setting with the widest “therapeutic window” is selected.
4. Implantation of the pulse generator (IPG)
   In a second stage on a different day, the electrode is connected subcutaneously to an implantable generator placed below the clavicle.

Initial programming typically begins 2–4 weeks after surgery, and optimal results may require 3–6 months of adjustments.

What are the outcomes and risks of DBS?

High likelihood of substantial improvement, with clearly defined risks.

In well-selected patients with accurate targeting:

• DBS of the VIM nucleus can reduce tremor by approximately 60–90%
• dramatically improve the ability to eat, write, and work
• reduce the need for high medication doses.

Potential complications include:

• Perioperative
  – Infection of implanted hardware
  – Edema
  – Intracerebral hemorrhage (rare).
• Postoperative / stimulation-related
  – Headache
  – Paresthesias
  – Balance disturbance
  – Ataxia
  – Usually improved by programming adjustments.
• Hardware-related
  – Skin erosion, lead fracture or migration,
  – generator issues requiring surgical revision.

For most patients, the functional and independence benefits outweigh surgical risks, provided that the decision is made thoughtfully with full patient education.