Chapter 25

Essential tremor (ET) is the most common cause of tremor and one of the most prevalent movement disorders affecting an estimated 10 million persons in the United States.1 The first descriptions of tremor date back to ancient times; however, it was not until the 1800s that ET was recognized as a distinct disorder. At that time, it was defined as a disorder that is often hereditary with persistent action tremor without other neurological signs. The term “essential tremor” was first used in the 1800s, but several other terms have been used to describe this disorder throughout the years such as senile tremor, benign tremor, familial tremor, and benign familial tremor. It was not until the later 1900s that the term “essential tremor” was consistently used in the medical literature.1 In medical terminology, the word “essential” is often used to describe a disorder in which the cause is unknown. Therefore, “essential tremor” refers to a disorder characterized primarily by tremor for which the cause is unknown.

### Primary Characteristics

ET is a neurological disorder characterized primarily by an action tremor including a kinetic tremor occurring during voluntary movement, and/or a postural tremor occurring when the affected body part is held against gravity.2 Intention tremor, a type of tremor in which the tremor is increased as the limb approaches a target, is also commonly seen in ET.2 Rest tremor is rarely seen in ET but has been reported in older patients with more advanced disease.3 During examination, it is important to make certain that the tremulous body part is relaxed and completely supported to assure the observed tremor is truly a resting and not a postural tremor. Tremor frequency usually ranges between 4 and 12 Hz. Older patients tend to have lower frequency tremor between 4 and 8 Hz, while younger patients generally have a higher frequency tremor ranging between 8 and 12 Hz.4

### Distribution

ET affects the upper extremities in approximately 95% of patients, and is generally a bilateral tremor.5 Hand tremor can cause significant disability in completing activities of daily living such as eating, dressing, drinking, and writing. Handwriting tends to be large and tremulous as opposed to the micrographia seen in PD.6 ET also affects the head in approximately 34% of patients.5 Head tremor generally occurs in combination with hand tremor. Less often, head tremor can occur in isolation in ET; however, in these cases, it is important to rule out cervical dystonia as the cause of the tremor. Other body parts that can be affected by ET include the lower extremities (20%), voice (12%), face (5%), and trunk (5%).5 It is not uncommon to see both the severity of the tremor and the range of body parts affected by the tremor increase as the disease progresses.

### Age of Onset and Disease Progression

ET can affect ...

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