Essential Tremor

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Introduction

Essential tremor (ET) is classified as a neurological disorder. It is commonly characterized as an uncontrollable shaking that occurs in various body parts, such as the head, chin, hands, arms, and also presents with a shaking voice due to affected vocal cords. ET is different from a resting tremor, which is associated with Parkinson’s, and is commonly classified as an action tremor (Abboud, 2011).

Mechanism of Injury / Pathological Process

The likelihood of acquiring ET has been shown to increase with age, in different ethnicities, and in persons with a family history of ET. The risk of acquiring ET has been shown to be more prevalent in older populations. An increased risk has also been found in Caucasians opposed to African-American populations.
Genetic factors have been linked to increased prevalence of ET with some studies suggesting potential linkages identified at the 3q13 and 2p22 chromosomes. However, there is a large discrepancy if genetic factors are a cause of ET, since other studies found only a moderate link (60-63%) in monozygotic twins and a low link (27-42%) in dizygotic twins. This is indicative that environmental factors likely play a role in the prevalence of ET's. A link in β-carboline alkaloids (harmine and harmane) has been found in subjects with ET, since high concentrations of β-carboline alkaloids were found in their blood.
β-carboline alkaloids are found in high meat diets and increased meat consumption has been linked with prevelance in persons with ET. An increased concentration of lead was also found in subjects with ET's. These environmental factors increase the risk for developing ET, and the risk of aquring ET increases when gentetics, age, and ethnicity of the person favourable ET development (Louis, 2001).

Epidemiology

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Diagnostic Procedures

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Clinical Presentation

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Definition

Essential tremor (ET) is classified as a neurological disorder. It is commonly characterized as an uncontrollable shaking that occurs in various body parts, such as the head, chin, hands, arms, and also presents with a shaking voice due to affected vocal cords. ET is different from a resting tremor, which is associated with Parkinson’s, and is commonly classified as an action tremor (Abboud, 2011).

Pathology

The likelihood of acquiring ET has been shown to increase with age, in different ethnicities, and in persons with a family history of ET. The risk of acquiring ET has been shown to be more prevalent in older populations. An increased risk has also been found in Caucasians opposed to African-American populations.
Genetic factors have been linked to increased prevalence of ET with some studies suggesting potential linkages identified at the 3q13 and 2p22 chromosomes. However, there is a large discrepancy if genetic factors are a cause of ET, since other studies found only a moderate link (60-63%) in monozygotic twins and a low link (27-42%) in dizygotic twins. This is indicative that environmental factors likely play a role in the prevalence of ET's. A link in β-carboline alkaloids (harmine and harmane) has been found in subjects with ET, since high concentrations of β-carboline alkaloids were found in their blood.
β-carboline alkaloids are found in high meat diets and increased meat consumption has been linked with prevelance in persons with ET. An increased concentration of lead was also found in subjects with ET's. These environmental factors increase the risk for developing ET, and the risk of aquring ET increases when gentetics, age, and ethnicity of the person favourable ET development (Louis, 2001).

Epidemiology: 

ET is considered to be one of the most, if not the most, common adult movement disorders (Louis, 1998). It is estimated to affect 0.9% of the population (Louis, 2010). The prevalence increases greatly with age. It is estimated to reach an average of 4.6% in the population over 65 years of age (Louis, 2010). Additionally, more recent studies indicate the potential of a slightly higher prominence of the condition in men than women (Louis, 2010). Finally, it is thought that further research could indicate differences in prevalence among different ethnic groups (Louis, 2010).

Assessment/Diagnosis:

The literature is somewhat variable on the method of diagnosis of ET. This is due to varied clinical presentations and a lack of agreement among specialists on the definition of ET (2). Despite variability and an inability to test for serological, pathological or radiological markers as a method of diagnosis, there are several clinical criteria which are used to differentiate tremor types (1). This clinical examination is very comprehensive and typically includes the following observations or tests (1) :

1. Observe the patient at rest and note any resting tremor or the head, hands or legs
2.  Ask the patient to stretch out arms to observe for postural tremor
3. Check finger-nose-finger movements to observe kinetic tremor

On assessment of ET, there should be no findings of any other focal neurological condition. Subjective findings include ….. A diagnosis of definite ET includes the following clinical criteria (1):

1. Postural tremor of moderate amplitude is present in a least one arm (although usually bilateral)
2. Tremor of moderate amplitude is present in at least one arm during at least four tasks
   a. Pouring water
   b. Using a spoon to drink water
   c. Finger-nose-finger maneuver
   d. Drawing a spiral
3.  Tremor must interfere with at least one activity of daily living (ADL)
4. Medications, hypothyroidism, alcohol use and other neurological conditions are not the cause of the tremor

The clinical criteria used for a “probably ET” are listed as follows (1):

1. Tremor of moderate amplitude is present in at least one arm during at least four tasks, or head tremor is present
2. Medications, hyperthyroidism, alcohol use and other neurological conditions are not the cause of the tremor

Any of the following objective findings which would indicate a tremor diagnosis other than ET: abnormal neurological exam findings, isolated voice tremor, isolated positon-specific or task-specific tremor and isolated tongue, chin or leg tremor (Ref 1 – author manuscript). Tremors associated with Parkinson’s Disease (PD) can be difficult to differentiate from ET. Key features such as asymmetric onset, resting tremor and a tremor while walking would indicate a parkinsonian origin and not ET (1).

Screening questionnaires can be used for diagnosis of ET but the generally only have a moderate (60-70%) sensitivity. (35, 36) Responses to these questionnaires generally correlated well to the clinical examination findings for those with definite or probably ET (36). Subjects with a diagnosis of mild ET from a clinical examination were most often screened as negative on the questionnaires. (36)

Clinical presentation: Julie

Treatment: 

References:

<u</u>Louis, D.E., Essential tremor. (2001). The New England Journal of Medicine. 345:887-891.

Abboud, H., Ahmed, A., Fernandez, HH. (2011). Essential tremor: choosing the right management plan for your patient. Cleve Clin J Med. 78(12):821-8.
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