Essential Tremor Within the Broader Context of Other Forms of Cerebellar Degeneration
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Essential Tremor Within the Broader Context of Other Forms of Cerebellar Degeneration Elan D. Louis 1
&
Phyllis L. Faust 2
# Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract Essential tremor (ET) has recently been reconceptualized by many as a degenerative disease of the cerebellum. Until now, though, there has been no attempt to frame it within the context of these diseases. Here, we compare the clinical and postmortem features of ET with other cerebellar degenerations, thereby placing it within the broader context of these diseases. Action tremor is the hallmark feature of ET. Although often underreported in the spinocerebellar ataxias (SCAs), action tremors occur, and it is noteworthy that in SCA12 and 15, they are highly prevalent, often severe, and can be the earliest disease manifestation, resulting in an initial diagnosis of ET in many cases. Intention tremor, sometimes referred to as “cerebellar tremor,” is a common feature of ET and many SCAs. Other features of cerebellar dysfunction, gait ataxia and eye motion abnormalities, are seen to a mild degree in ET and more markedly in SCAs. Several SCAs (e.g., SCA5, 6, 14, and 15), like ET, follow a milder and more protracted disease course. In ET, numerous postmortem changes have been localized to the cerebellum and are largely confined to the cerebellar cortex, preserving the cerebellar nuclei. Purkinje cell loss is modest. Similarly, in SCA3, 12, and 15, Purkinje cell loss is limited, and in SCA12 and 15, there is preservation of cerebellar nuclei and relative sparing of other central nervous system regions. Both clinically and pathologically, there are numerous similarities and intersection points between ET and other disorders of cerebellar degeneration. Keywords Essential tremor . Cerebellar degeneration . Spinocerebellar ataxia . Clinical . Neuropathology
Introduction Essential tremor (ET) is a chronic, progressive neurological disease whose hallmark clinical feature is kinetic tremor of the upper limbs [1, 2]. It is among the most prevalent movement disorders and is the most prevalent tremor disorder [3], with an estimated 7 million affected people in the USA (i.e., approximately 2.2% of the entire population of the USA) [4] and high estimates of prevalence (i.e., number of cases per 100,000 population) in numerous countries [3]. Despite being so common, the underlying pathomechanisms of ET remain surprisingly enigmatic * Elan D. Louis [email protected] 1
Department of Neurology and Therapeutics, University of Texas Southwestern Medical Center, Dallas, TX, USA
2
Department of Pathology and Cell Biology, Columbia University Irving Medical Center and the New York Presbyterian Hospital, New York, NY, USA
[5–7]. Even localizing the site of primary pathology within the brain has been a major challenge. There had been no systematic collection of ET brains until 2003 [8, 9]. During the 100-year period from 1903 to 2003, there were only 15 published postmortems [8], mainly comprising isolated case reports wi
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