Essential tremor, previously referred to as benign essential tremor or familial tremor, refers to a progressive postural tremor that is symmetrical, rhythmic, and involuntary. It mostly involves the hands and forearms in most but can involve the head, jaw, voice in others. It is absent at rest and present during posture (holding part of the body in a fixed position against gravity) and intentional movements.
It is the most common type of tremor and one of the most common movement disorders globally. The prevalent increases with age but in familial cases (autosomal dominant inheritance) the onset is during childhood. Sporadic cases usually occur over the age of 40.
Pathophysiology
The aetiology of essential tremor is not currently known. However, as previously mentioned, there is a genetic component. Genome-wide association studies have implicated the genes LINGO1 and SLC1A2.
What occurs with essential tremor is not fully understood. It seems as if there is dysfunction of the cerebellum, brainstem and thalamus. A finding that may point to a GABA-ergic dysfunction is the fact that patients who have essential tremor report their tremor improving with GABA-ergic medications and substances (such as alcohol, benzodiazepines, barbiturates and gabapentin). However, a 2018 study was unable to find any GABA deficiency in the cerebellum.
š¢ Classification
We can classify tremors as either:
- Rest tremors - these occur when the body is rested against something that supports it against gravity. For example, resting your hand on the table. This occurs in Parikinsonās disease or other extrapyramidal disease.
- Action tremors - tremors that occur during voluntary movement. They can be subdivided into:
- Postural tremor - these occur when the body is held in a fixed position against gravity. Essential tremor is a postural tremor. Other examples include physiological tremor, anxiety, alcohol, drugs, neurosyphilis, Wilsonās disease.
- Kinetic tremor - these occur when there is voluntary movement in the upper body. If it gets worse when there is movement towards an intended target it is known as an intention tremor. They are associated with brainstem or cerebellar dysfunction and multiple sclerosis.
ā ļø Risk factors
- Old age
- Family history
š· Presentation
- āļø AĀ bilateral upper limb action tremor, withĀ absence of other neurological signsĀ such as dystonia, ataxia, or parkinsonism is the core sign of essential tremor.
The characteristics of the tremor are:
- Fine tremor (6-12 Hz)
- Symmetrical
- More prominent with voluntary movement
- Worse when tired, stressed or after caffeine
- Improved by alcohol benzodiazepines, barbiturates and gabapentin
- Absent during sleep
- VocalĀ orĀ head tremor - the tremor may include parts other than the upper body such as the head or voice.
Patients often report a long history ofĀ progressive functional declineĀ in activities that require use of theirĀ upper extremitiesĀ due to tremor. Activities of daily living such asĀ writing,Ā eating,Ā drinking, andĀ dressingĀ are typically impacted. TheĀ use of straws and of cupsĀ with lids, andĀ delegating responsibilitiesĀ to a spouse or carer, are common historical presentations.
Parkinsonās tremor | Essential tremor |
Asymmetrical | Symmetrical |
4-6 hertz | 6-12 hertz |
Worse at rest | Improves at rest |
Improves with intentional movement | Worse with intentional movement |
Other Parkinsonās features | No other Parkinsonās features |
No change with alcohol | Improves with alcohol |
š Investigations
āļø Essential tremor isĀ clinical diagnosis. Once suspected, aĀ thorough evaluation of functional and psychosocial disabilitiesĀ should be performed using objective scales to determine the need for pharmacotherapy.
Further investigations may be warranted to rule out other potential causes of tremor. This includes:
- Neurological examination
- Blood tests
- Neuroimaging
š§° Management
There is no definitive treatment for essential tremor. The tremor is not harmful and does not require treatment if it is not causing functional or psychological problems.
- Medications that may improve symptoms are:
- š„Ā PropranololĀ
- š„Ā PrimidoneĀ - a barbiturate anti-epileptic medication. It may triggerĀ acute intermittent porphyria.
- š„ Other beta blockers - such as atenolol,Ā sotalol.
- š„OtherĀ anticonvulsantsĀ - such as gabapentin,Ā topiramate, BZD's likeĀ alprazolam,Ā clonazepam.
- InĀ drug-resistantĀ cases:
- Deep brain stimulationĀ (DBS)
- Thalamotomy
Alternatives (ifĀ propranololĀ andĀ primidoneĀ are unresponsive or contraindicated):