Definition and Overview
Essential tremor (ET) is the most common movement disorder in adults. It is characterized by rhythmic, repetitive trembling primarily in both hands during postural maintenance (postural tremor) or intentional movement (kinetic tremor), with improvement at rest.
The prevalence is approximately 0.4-3.9% in all adults, rising to about 5% in those aged 65 and older [1]. Family history is common, and while previously classified as a benign condition, recent attention has focused on its progressive neurodegenerative aspects.
Causes and Pathophysiology
The pathophysiology of essential tremor centers on overactivity and functional abnormalities of the cerebello-thalamo-cortical circuit. In particular, abnormal oscillation of the olivocerebellar pathway between the inferior olive and cerebellum is believed to generate the tremor.
Genetic factors are also important. Family history is confirmed in approximately 50-70% of patients, and autosomal dominant inheritance patterns are common. Related genes such as LINGO1 and SLC1A2 have been reported, but a single causative gene has not yet been established.
Symptoms
Tremor primarily appears symmetrically in both hands and forearms, prominent during daily activities such as writing, eating, and drinking. The main symptoms include:
- Hand tremor: worsens with action, improves at rest (key differentiator from Parkinson's disease)
- Head tremor: yes-yes (vertical) or no-no (horizontal) direction
- Voice tremor: trembling voice during speech
- Leg tremor is rare and typically accompanies severe cases
Temporary reduction of tremor after alcohol consumption is observed in approximately 50-70% of patients [1].
Diagnosis
Essential tremor is a clinical diagnosis based on characteristic history and physical examination confirming action tremor. It is important to rule out hyperthyroidism, drug-induced tremor, Parkinson's disease, and cerebellar disorders.
A dopamine transporter scan (DaT scan) can differentiate from Parkinson's disease. In ET, the DaT scan shows normal findings, while in Parkinson's disease, striatal dopamine transporter binding is reduced.
Nerve conduction studies and brain MRI are performed when atypical features or secondary causes need evaluation.
Treatment
Pharmacotherapy
Propranolol is a non-selective beta-adrenergic blocker and the first-line treatment, reducing tremor amplitude in approximately 50-60% of patients [2]. Caution is needed in patients with asthma, bradycardia, or hypotension.
Primidone is an anticonvulsant with similar efficacy, recommended as a co-first-line treatment [3]. It is started at low doses due to initial drowsiness and dizziness.
Other medications including gabapentin, topiramate, and alprazolam may be considered as second-line treatments.
Surgical Treatment
For medication-refractory severe cases, the following surgical options are considered:
- Thalamic deep brain stimulation (DBS): Electrodes implanted in the ventral intermediate nucleus (VIM) of the thalamus deliver high-frequency stimulation, significantly reducing tremor in approximately 60-80% of cases [3].
- MRI-guided focused ultrasound thalamotomy (MRgFUS): A non-invasive method that destroys the thalamic VIM using focused ultrasound without opening the skull.
Prognosis
Essential tremor is not life-threatening but tends to progress slowly. It can affect daily functioning and reduce quality of life. Symptoms can be controlled in most patients with pharmacotherapy, and surgical treatment is selected for cases with significant functional impairment.