Essential Tremor

Most patients will report tremor that starts from one upper extremity and then affects the other. It is almost always limited to the upper extremities. Tremor is initially intermittent but overtime becomes persistent. The amplitude is worsened by hunger, emotion, fatigue and extremes of temperature. Tremors may also involve the head and face. The tremor is noticed to resolve during sleep and ethanol intake may temporarily reduce its amplitude in up to 70% of cases. There is a family history of tremor in up to 60% of cases. When a tremor is visible, it should be considered pathologic [6]. During physical examination, features of Parkinson disease like rigidity and bradykinesia should be ruled out.

• There are no laboratory investigations to diagnose essential tremors. Laboratory studies are only considered if the history and physical examination are not indicative of essential tremor. Some of these laboratory studies are: Serum electrolytes, blood urea nitrogen, serum creatinine, thyroid function test, and liver function tests. These tests will help to identify other cause of tremors. Serum ceruloplasmin should also be done to rule out Wilson disease [7]. 
• Electromyography can be used to assess frequency, amplitude and rhythmicity. Accelerometry can also be used.
• Computed tomography and magnetic resonance imaging are normal in patient with essential tremor. However these imaging techniques are done to rule out structural and/or inflammatory lesions of the brain [8]. 

• The initial management of essential tremor is medical. Propranolol and primidone are the bases of maintenance medical management of this condition. Usually, propranolol is started first in younger patients while primidone is started first in older patients [9]. 
• These drugs generally reduce tremor amplitude in 70% of cases. Some other medications that may be tried if these are unsuccessful are beta-1 receptor antagonist, beta-2 receptor antagonist and clonazepam. Others are Botulinum toxin, topiramate, gabapentin, clozapine and mirtazapine. Alcohol may be used in patients who only require intermittent tremor reduction [10].
• Patients with disabling, medically intractable upper extremity tremors should be considered for surgery. Surgical procedures that can be performed include thalamic ventralis intermedius nucleus deep brain stimulation and stereotactic thalamotomy. Both of these procedures offer a high rate of tremor reduction in the contralateral arm as well as reducing head and voice tremor. Thalamic stimulation is however now being considered the procedure of choice as it has the advantage of being adjustable.
• There is a very high risk of dysarthria and cerebral hemorrhage in bilateral thalamotomy. 

The mortality rate in essential tremor is basically the same as that for the general population. There is however disability from essential tremor with up to 15% of affected individuals being seriously disabled. There is a generally a decreased quality of life primarily due to loss of function.

The cause of essential tremor is still unknown. In absence of any consistently associated pathologic findings, some hypothesis have been promulgated. One of such is the possible involvement of the cerebellar-brainstem-thalamic-cortical circuits. Another is that it is as a result of an abnormally functioning central oscillator that is involves the inferior olivary nucleus. A third hypothesis is that the pathophysiology of essential tremors is diverse.

Some of the factors that have been linked to its etiology include a potent tremor-producing neurotoxin called Harmane and increased glucose consumption in the medulla. There are also multiple etiologies that have been linked with genetics [2].

The prevalence of essential tremor is about 5.6% of the general United States population, and only about 11% of those affected seek medical attention. The prevalence in the internal community is about 3.9%. It has a bimodal peak age of occurrence, in late adolescence/early adulthood and in the older age group and the mean age of occurrence is between 35 to 45 years. It usually manifests by age 65 years and the amplitude of the tremor increases over time. The race demographic has not been well studied but there appears to be a higher prevalence in Caucasians than in African-Americans. It occurs with equal frequency in both sexes [3].

• The pathophysiology, like the etiology is multifactorial with many of the causes likely to be genetic. Transmission may be autosomal-dominant with incomplete penetrance. Some susceptibility loci have been identified [4]. 
• There are other proposed methods of pathogenesis.
• There is increased blood concentration of harmane in the blood of affected individuals and this is likely due to metabolic alterations. PET scans have also showed bilateral overactivity of cerebellar circuitry and increased regional blood flow in the medulla of individuals with essential tremor.
• Findings during autopsy like loss of Purkinje cells, dentate nucleus abnormalities, and lewy bodies in the locus ceruleus are pathologic abnormalities of the brain stem that support the hypothesis that essential tremor is a neurodegenerative disease [5].

There is no known way to prevent this condition. Small quantities of alcohol have been shown to reduce tremors. The potential for abuse should however be considered.

Essential tremors are also known as kinetic tremor as they intensify when the muscle groups are put in play [1].  It is the most common movement disorder and it usually affects both upper extremities. The etiology is unknown but there is a debate as to whether or not it is a neurodegenerative disease.

• Definition: Essential tremor is a movement disorder characterized by involuntary movement of some muscle groups. It typically affects the upper arms and sometimes the face and head. No underlying disease is usually found to be responsible for these movements.
• Cause: The cause is unknown. It is however believed to have some familial links as genes can be passed from parents to offspring. It may also be due to abnormal functioning of the part of the brain responsible for movement. 
• Symptoms: The main symptom is tremor and it is sometimes the only symptom. It is most likely going to start from one hand and then extend to the other. There may also be head nodding and quivering of the voice due to the effect of the tremors.
• Diagnosis: This is usually gotten from the history and physical examination. Laboratory tests will be ordered to rule out other causes of tremors, if no cause it found, it is essential tremor. Imaging tests like MRI will also be done to rule out brain disease. Some test may be required to check the intensity of the tremor.
• Treatment: Treatment involves the use of drugs to control the tremors. If the drugs fail, some surgical techniques may be employed.

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8. Nicoletti G, Manners D, Novellino F, et al. Diffusion tensor MRI changes in cerebellar structures of patients with familial essential tremor. Neurology 2010; 74:988.
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10. Pahwa R, Busenbark K, Swanson-Hyland EF, et al. Botulinum toxin treatment of essential head tremor. Neurology 1995; 45:822.