Essential tremor

Essential tremor describes a chronic, progressive, predominantly bilateral upper limb, action tremor syndrome, present without parkinsonism, dystonia and ataxia. Essential tremor associated with other 'soft' neurological signs is known as essential tremor plus.

Epidemiology

Essential tremor is one of the most common movement disorders. Its prevalence increases with age, and is estimated to affect up to 5% of the population over the age of 65 years ¹. However, the condition can also be seen in younger patients, including in the pediatric demographic, albeit rarely ¹. There is thought to be either no gender predilection or a slight male predominance ¹.

Clinical presentation

Essential tremor:

• action 4-12 Hz tremor, progressing insidiously but must be present for at least 3 years duration ^1-4

  • the action tremor is kinetic (including simple or intention) more-so than postural ¹

  • a rest tremor may also be present in the minority of cases, especially in advanced stages, but never in isolation ^1,2

  • there is no change in tremor frequency with weight-loading, unlike an enhanced physiological tremor ⁴

• tremor initially and predominantly affects the bilateral upper limbs ^1-4

  • while bilateral, there may be mild asymmetry ^1,2

  • can also involve the head, tongue, voice, and lower limbs as the condition progresses ^1-4

• alcohol consumption improves the tremor in half of cases ¹

Essential tremor plus:

• aforementioned features of essential tremor

• presence of 'soft' neurological signs such as minor gait disturbance (e.g. difficulties with tandem gait), mild cognitive impairment, etc. ^1-4

  • does not include 'hard' neurological signs such as parkinsonism, dystonia, or ataxia ^1-4

Pathology

The exact aetiopathogenesis of essential tremor is yet to be fully elucidated. The primary hypothesis is that there is dysfunction in the cerebello-thalamo-cortical circuit ^2,4,5. There is also thought to be a strong genetic component to essential tremor, given a family history may be present in up to half of all patients, however, no genes have yet been implicated ¹.

Radiographic features

Traditional neuroimaging, such as CT or MRI brain, are normal in essential tremor ^1,5,6. Thus, these routine radiological studies have very little role in the diagnosis of essential tremor, which is ultimately a clinical one ^1,5,6.

Notably, I-123 ioflupane SPECT (DaTScan) is also usually normal, and this finding is used by some to differentiate essential tremor from some of its clinical mimics that have niagrostriatal degeneration (e.g. idiopathic Parkinson disease) ^5,6.

Treatment and prognosis

Potential management can include non-pharmacological, pharmacological, and surgical measures ^1,7,8.

• non-pharmacological: non-invasive neuromodulation (e.g. ulnar or radial nerve stimulation), tremor-canceling devices ^1,8

  • although alcohol consumption may improve the tremor in half of cases, this is not an appropriate recommendation

• pharmacological:

  • first-line: propranolol, primidone ^1,7

  • other agents: topiramate, gabapentin, benzodiazepines, botulinum toxin (to upper limb muscles), etc. ^1,7

• surgical:

  • thalamotomy ^1,7

  • deep brain stimulation to ventral intermediate nucleus of thalamus ^1,7

  • MR-guided focused ultrasound to ventral intermediate nucleus of thalamus ^1,7

History and etymology

The first recorded use of "essential tremor" was by Italian physician Pietro Burresi in 1874 ⁹. However, there are likely documented cases of this tremor syndrome in the literature many years prior to this date ⁹.

Differential diagnosis

• idiopathic Parkinson disease (especially tremor-predominant phenotypes) and other causes of parkinsonism

• enhanced physiologic tremor (e.g. due to hyperthyroidism)

• cerebellar tremor

• functional tremor

• Wilson disease