Essential tremor and cognitive impairment: who, how, and why.

BACKGROUND AND AIMS: Recent years have witnessed the switch from considering essential tremor (ET) a monosymptomatic disorder to consider it as part of a spectrum, including other neurological signs, such as mild cognitive impairment and dementia, thus defining it as "ET plus." There are few data on cognitive impairment in ET patients. The aim of this review is to analyze the clinical characteristics of ET patients developing cognitive impairment, their neuropsychological profile, the underpinning mechanisms, and the possible biomarkers. METHODS: The authors performed a narrative review on cognitive decline in essential tremor, including articles written in English since the year 2000. DISCUSSION: The most recent pathogenetic theories of cognitive impairment in ET rely on the cerebellar dysfunction, being part of the Cerebellar Cognitive Affective Syndrome spectrum. Cognitive impairment in ET patients could be assessed through many tests that demonstrate the involvement of different domains, such as attention, executive functions, and language. There are some clinical characteristics of ET that may indicate a greater risk of developing cognitive impairment, namely, cerebellar symptoms, falls, age at onset, and family history. However, there are no established clinical, neurophysiological, neuropathological, and fluid biomarkers of cognitive impairment in ET. CONCLUSIONS: Increasing data are showing in ET the presence of cerebellar symptoms and cognitive impairment. Further studies are needed to better understand cognition in ET patients, and to define the boundary between ET and ET plus, since deeper phenotyping might have important clinical and therapeutic implications.