Essential tremor

Notes

Overview

Essential tremor is a type of action tremor that is very common in the general population.

Essential tremor is considered the most common type of action tremor (i.e. tremor during voluntary muscle contraction) that typically involves the hands and is bought out by anti-gravity positions (e.g. outstretched hands).

Essential tremor is associated with family history and often shows an autosomal dominant pattern of inheritance. It was previously termed ‘benign essential tremor’, however, the term benign has been dropped because it can cause a severe and disabling tremor in some individuals.

Epidemiology

A family history of essential tremor may be observed in 30-70% of cases.

The estimated prevalence of essential tremor is 1% worldwide. Development of this type of action tremor increases with age and there is often a family history. The inheritance is suspected to be autosomal dominant. There is thought to be a slight male predominance.

Aetiology & pathophysiology

The pathophysiology of essential tremor remains poorly defined.

Essential tremor is associated with a strong family history but the exact cause remains unknown. This is probably due to the heterogeneity of the condition (i.e. it is not a single disorder, but represents a spectrum of similar conditions).

Several variants in at-risk genes have been identified from genome-wide association studies. There is not complete concordance in monozygotic twins suggesting environmental factors may also be important (i.e. both twins would develop the condition if there was complete concordance). The exact mechanisms leading to the tremor within the nervous system remain poorly defined.

Clinical features

It is characterised by a bilateral kinetic (on voluntary movement) and/or postural (during voluntarily maintained position) tremor of the hands and arms.

Essential tremor is an action tremor that occurs on movement. This may be during voluntary movement (i.e. simple kinetic tremor) or when the affected body part is voluntarily maintained in a certain position (i.e. postural tremor). It is considered a progressive disorder that worsens over time.

Affected sites

Essential tremor most commonly affects the hands and arms. It is usually bilaterally.

Body parts affected can include:

  • Hands
  • Arms
  • Head
  • Voice
  • Face
  • Trunk

Characteristics

Classically seen in the hands and arms when outstretched or required to perform a specific task (e.g. drinking from a cup). The tremor is usually absent when the hand/arms are relaxed and supported against gravity.

Essential tremor affecting the head may lead to a typical nodding ‘yes-yes’ or shaking ‘no-no’ tremor. There may also be a tremor of the voice that can be determined by asking the patient to hold a note. It rarely affects the legs and this should make you consider Parkinson’s disease.

Frequency and amplitude

Any tremor may also be described in terms of frequency and amplitude:

  • Frequency: this is essentially how quick the tremor is, or in other words, the oscillations (back and forth movement) per second. It is measured in cycles per second (Hertz - Hz)
  • Amplitude: this is essentially the amount of movement, or in other words, the degree of displacement of the limb or body part. Large amplitude tremors (i.e. associated with more movement) are usually more disabling

Essential tremor is typically a moderate to high-frequency tremor at 6-12 Hz with low amplitude. Particular postures or actions may precipitate a higher amplitude (i.e. greater movement).

Exacerbating and relieving factors

An essential tremor characteristically improves with a small amount of alcohol. Unlike a physiological tremor, it is not worsened by caffeine.

Associated features

Tremor should be the only feature and the absence of other neurological signs is characteristic of the diagnosis. However, some neurological signs may be observed in certain cases including gait difficulty and mild cognitive dysfunction.

Diagnosis & investigations

The diagnosis of essential tremor is made clinically.

A diagnosis of essential tremor is typically based on the following four features:

  • Isolated upper limb action tremor
  • With/without tremor in other sites (e.g. head)
  • Duration >3 years
  • No other neurological features

Investigations have a limited role in essential tremor, but may be requested for atypical cases or when an alternative diagnosis is suspected (e.g. Physiological tremor, Parkinson’s disease). Structural brain imaging with MRI or specialised CT imaging (e.g. DaTscan) may be used, particularly when Parkinson’s disease is suspected or cannot be distinguished from essential tremor.

A dopamine transporter scan (DaTscan) can be used to reliably distinguish Parkinson’s disease or Parkinsonism from patients with essential tremor. It is a specialised type of scan that looks for loss of dopaminergic neurons in the basal ganglia.

Management

Management of essential tremor depends on its severity.

Basic management steps should be completed first including removing any potential precipitant that makes the tremor worse. Pharmacological treatment may be considered in patients with persistent functional or psychological disability caused by the tremor. More invasive treatments are available for refractory cases.

Ultimately, essential tremor is a progressive disease and patients should be warned that symptoms will worsen over time.

Pharmacological treatment

Several medical therapies may be offered to patients with persistent functional or psychological disability. These include:

  • Propranolol: non-selective beta-blocker used in many conditions to reduce sympathetic activity
  • Primidone: anti-epileptic drug that has an unclear mechanism. Possibly activates gamma-aminobutyric acid (GABA) receptors and alters voltage-gated sodium channels

Propranolol is commonly chosen first-line due to side-effect profiles. Both have been associated with reduction in tremor amplitude by 50%. Importantly, some patients may not see an effect.

Second-line options if these medications fail include:

  • Switching to the alternative first-line
  • Add both first-line medications in combination
  • Add or switch to another agent (e.g. gabapentin, topiramate)

Additional therapies

Patients with refractory tremor despite pharmacotherapy may be offered a range of further treatments with variable efficacy. This is highly specialist but options may include:

  • Neuromodulation (e.g. nerve stimulation devices)
  • Botulinum toxin injections
  • Deep brain stimulation

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