In this article, the author reviews new studies related to the pathogenesis of essential tremor, including Purkinje cell pathology as well as LINGO1 and SLC1A2 genes. Clinical diagnosis of tremor disorders and treatment strategies for essential tremor are described in detail.
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• Two subtypes of essential tremor pathology have been identified: a primarily cerebellar variant with Bergmann gliosis and Purkinje cell torpedoes, and a Lewy body variant.
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• Propranolol and primidone are useful first-line medications for essential tremor.
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• Deep brain stimulation surgery continues to be useful for severe, medication-resistant tremor.
Historical note and terminology
The history of tremor can be roughly divided into 2 phases. The first and largely descriptive phase began in the 19th century; clinicians were able to recognize the principal manifestations of tremor and characterize and classify different forms of tremor based on clinical patterns and their relationships with known pathologies. GF Most provided 1 of these reports of action tremor in 1836. The first known use of the term “essential tremor” was traced to Pietro Burresi in 1874 (138). The names of Romberg, Parkinson, Gowers, and Charcot all contributed extensively to our knowledge and laid the groundwork for the second phase. Charcot collected handwriting samples from his patients and differentiated between tremulous handwriting in essential tremor and micrographic handwriting in Parkinson disease (74). Gowers described rest tremor at the metacarpal-phalangeal joints as someone beating a small drum (74).
The second phase began in the latter part of this century with the explosion of newer technologies that were able to further identify the pathophysiology of tremor. This explosion also contributed to our further ability to carefully classify clinical syndromes not only in terms of their phenomenology and pathology but also their neurophysiology. This phase has led to significant improvements and advances in treatment culminating presently with surgical therapies and deep brain stimulation.
Descriptions of the contributions of early American investigators to the understanding of tremors (115), and documentation of essential tremor in Samuel Adams, an early American patriot (129), provide an interesting historical perspective on tremor.
The diagnosis, classification, etiology, pathophysiology, and treatment have been controversial in the past, but progress has been made in all of these parameters. The 2018 Consensus Statement from the International Parkinson and Movement Disorder Society retains characteristic tremor syndromes but also evaluates them on clinical characteristics on Axis 1 and etiology on Axis 2 (22).
The concept of essential tremor as a single, monosymptomatic entity has changed over time (65; 133). The 2018 consensus statement addresses this heterogeneity by recognizing that there may be additional features such as dystonia, bradykinesia, cognitive impairment (Axis 1), and a heterogenous etiology (Axis 2). This improved classification system should allow for more success in clinical research of essential tremor. Given the significant potential for disability in both social and occupational settings due to tremor (61), the word “benign” was removed from the term “benign essential tremor” (147).