Non-motor symptoms in essential tremor: A review of the current data and state of the field.
BACKGROUND
The motor features of essential tremor (ET) include its hallmark element, kinetic tremor, yet non-motor features are increasingly being recognized as an accompanying part of what was previously viewed as a solely motor disorder. Given the evolving state of the ET field with respect to these non-motor features, the purpose of this manuscript is to critically review the current data.


METHODS
A PubMed search was conducted on July 1, 2015. The term "essential tremor" was crossed in sequential order with 13 additional search terms (e.g., "cognitive", "dementia", "depression"). The total number of unique hits was 322.


RESULTS
Numerous studies seem to substantiate the presence of a range of non-motor features occurring in excess in ET cases compared to age-matched controls. These comprise cognitive features (including a full spectrum from mild cognitive difficulty through to frank dementia), psychiatric (including depression, apathy, anxiety, and personality characteristics), sensory (hearing and possibly olfactory abnormalities), and other non-motor features (e.g., sleep dysregulation). Emerging evidence suggests that some of these features could be primary disease features that pre-date motor features of ET.


CONCLUSIONS
The presence of numerous non-motor features in ET is increasingly evident. The biological basis of these features deserves additional study.
Department of Neurology, Yale School of Medicine, Yale University, New Haven, CT, USA; Department of Chronic Disease Epidemiology, Yale School of Public Health, Yale University, New Haven, CT, USA; Center for Neuroepidemiology and Clinical Neurological Research, Yale School of Medicine, Yale University, New Haven, CT, USA. Electronic address: elan.louis@yale.edu.
Elan D
ED
Louis
D000818:Animals; D001007:Anxiety / Q000175:diagnosis / Q000453:epidemiology / Q000523:psychology; D057565:Apathy; D003072:Cognition Disorders / Q000175:diagnosis* / Q000453:epidemiology / Q000523:psychology; D003704:Dementia / Q000175:diagnosis / Q000453:epidemiology / Q000523:psychology; D003863:Depression / Q000175:diagnosis / Q000453:epidemiology / Q000523:psychology; D020329:Essential Tremor / Q000175:diagnosis* / Q000453:epidemiology / Q000523:psychology; D006801:Humans; D001523:Mental Disorders / Q000175:diagnosis* / Q000453:epidemiology / Q000523:psychology; D012678:Sensation Disorders / Q000175:diagnosis* / Q000453:epidemiology / Q000523:psychology; D013223:Statistics as Topic
Cognition; Dementia; Essential tremor; Non-motor; Psychiatric