Essential tremor

Essential tremor
Name	Essential tremor
Synonyms	Benign essential tremor, familial tremor
Caption	Illustration of a hand tremor.
Field	Neurology
Symptoms	Rhythmic shaking, typically of hands, head, or voice
Complications	Difficulty with fine motor tasks, social embarrassment
Onset	Any age, most common after 40
Duration	Lifelong
Causes	Unknown, genetic component suspected
Risks	Family history, age
Diagnosis	Based on symptoms, neurological exam, ruling out other conditions
Differential	Parkinson's disease, dystonia, hyperthyroidism
Prevention	None known
Treatment	Propranolol, primidone, deep brain stimulation, focused ultrasound
Medication	Beta blockers, anti-seizure drugs
Prognosis	Progressive but not life-threatening
Frequency	~1% of all ages, up to 5% over 60

Essential tremor. It is a common neurological disorder characterized by involuntary, rhythmic shaking, most often affecting the hands, but also potentially the head, voice, and other body parts. The tremor typically occurs during voluntary movement, such as when writing or holding a cup, a pattern known as an action tremor. While not life-threatening, it can be progressive and significantly impact daily activities and quality of life, leading to social withdrawal and disability.

Signs and symptoms

The primary sign is a postural and kinetic tremor, most frequently seen in the hands and arms, which worsens during purposeful movement like using utensils. A tremor of the head and neck may appear as a "yes-yes" or "no-no" motion, while vocal tremor affects the larynx, causing a shaky voice. Symptoms often begin asymmetrically and are exacerbated by factors like stress, caffeine, fatigue, and low blood sugar. In advanced cases, individuals may experience difficulty with handwriting, drinking from a glass, or using tools, and some develop a mild gait disturbance.

Causes and pathophysiology

The exact cause remains unknown, but a strong genetic component is evident, with many cases showing autosomal dominant inheritance. Research has linked some familial cases to genetic variations on chromosomes such as ETM1, ETM2, and ETM3. Pathophysiologically, the tremor is believed to originate from abnormal oscillatory activity within a network of brain structures including the cerebellum, inferior olivary nucleus, thalamus, and motor cortex. Dysfunction in GABA-ergic inhibition within the cerebellothalamocortical pathway is a leading hypothesis, though the roles of beta-adrenergic receptors and glutamate signaling are also under investigation.

Diagnosis

Diagnosis is primarily clinical, based on history and a neurological examination that observes the characteristic tremor. There is no definitive diagnostic test, so the process involves ruling out other conditions. Key differential diagnoses include Parkinson's disease, which features a resting tremor, and other disorders like dystonia, hyperthyroidism, or tremor induced by amiodarone or lithium. Physicians may use rating scales like the Fahn-Tolosa-Marin Tremor Rating Scale to assess severity. In complex cases, DaTscan imaging can help distinguish it from Parkinsonism.

Treatment

First-line pharmacological treatments include the beta-blocker propranolol and the anti-seizure medication primidone. Other medications like gabapentin, topiramate, or benzodiazepines such as alprazolam may be used. For severe, medication-resistant tremor, surgical interventions are considered, most commonly deep brain stimulation targeting the ventral intermediate nucleus of the thalamus. Non-invasive options include MRI-guided focused ultrasound thalamotomy, a procedure approved by the Food and Drug Administration. Botulinum toxin injections can be effective for head and voice tremor, and lifestyle modifications like avoiding caffeine are recommended.

Epidemiology

It is one of the most prevalent movement disorders, affecting approximately 1% of the general population worldwide and up to 5% of individuals over the age of 60. Incidence and prevalence increase significantly with age, though it can begin at any time from childhood to late adulthood. Studies, including those from the Framingham Heart Study, suggest no significant difference in prevalence between men and women. A positive family history is found in about half of all cases, indicating a strong hereditary pattern.

Prognosis and impact

The tremor is generally progressive, with the amplitude of shaking slowly increasing over decades, though the rate of progression varies widely. It is not associated with reduced life expectancy, but it can cause substantial functional and psychosocial disability. Many individuals experience social anxiety, embarrassment, and may avoid social situations or careers requiring steady hands, impacting participation in activities like musical performance. While distinct, some studies suggest an increased long-term risk of developing Parkinson's disease or mild cognitive impairment compared to the general population.

Category:Movement disorders Category:Neurological disorders