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Introduction
Essential tremor is a syndrome defined as a “bilateral upper extremity action tremor” and is among the most common movement disorders in adults.1 As life expectancy increases, the prevalence of essential tremor increases, and the number of patients with essential tremor presenting in the office for treatment is thus growing. The historical practice of grouping all action tremors together may partially explain both the difficulties in identifying genetic causes and patients’ variable responses to treatment.
Decades after their initial study, propranolol and primidone remain the first line oral drugs for essential tremor. However, only about half of the patients taking these drugs have a significant reduction in the amplitude of tremor.2 Little is known about the long term efficacy of treatments, as few trials have had long term follow-up. Very few interventions have class I evidence for their efficacy. The emergence of surgical alternatives for treatment offers new options for the most severely affected patients. In the past decade, novel treatments ranging from chemodenervation to noninvasive neuromodulation bring new excitement into the field. The goal of this review is to summarize the clinical features associated with the condition, the recommended changes in classification, and the current treatment options.
Epidemiology
Worldwide, the crude prevalence rates of essential tremor in adults range from 0.4% to 6%.34 Essential tremor affects approximately 1% of the population and 4-5% of people aged over 65 years.56 Studies suggest a bimodal age of onset.7 A clinical study of 978 patients with probable or definite essential tremor identified an early onset group with age 24 years or less and an older onset group with age 46 years or above.8 A retrospective chart review of 211 children found that the onset can be as early as birth, but the mean onset age was 9.7 (SD 5.6) years.9 Essential tremor in children has a male predominance that ranges from 1.6:1 to 3:1. Although adult onset essential tremor is not thought to have a sex imbalance, a population study of 2117 older adults also found a significant male predominance in the 46 patients with essential tremor (χ2=5.0, P=0.03).3
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