An increasing number of independent studies from around the world (Italy, first study in 2001; USA; Spain; Germany; Turkey; Korea) are now showing that, on average, essential tremor (ET) cases have poorer cognitive performance than age-matched controls. These cognitive changes are not strictly subclinical and they have been associated with greater functional difficulty. There is also an emerging understanding that the cognitive problems in ET patients are not necessarily static, can become severe, and that the rate of progression seems to be above and beyond that expected in age-matched people without ET. A cross-sectional epidemiological study reported an association between ET and mild cognitive impairment (MCI) (odds ratio 1.57), and several prospective, population-based, epidemiological studies, one in Madrid and the other in New York, demonstrated an association between ET and both prevalent and incident dementia. In these studies, 11.4–25.0% of ET cases had prevalent dementia vs. 6.0–9.2% of controls. Furthermore, in both studies, the risk of incident dementia at follow-up was higher among individuals with baseline ET vs. those without baseline ET (relative risk 1.64–1.89).1 A third study also found that a subset of ET cases had a similar increased risk of dementia (relative risk 2.1). ET patients with cognitive problems are not simply older adults with ET that happen to also have dementia (i.e., a chance co-occurrence).2 Studies reporting the presence of dementia in ET compare ET cases with age-matched controls, and show a higher prevalence of dementia in ET, thereby indicating that dementia is disease-linked and not merely age-linked. By analogy, the cognitive problems in Parkinson’s disease (PD) are not just “old people” with MCI or dementia who happen to also have PD; there is both clinically and pathologically a separable PD cognition entity. The same is likely true for ET. That is, ET itself appears to be a risk factor for developing a gradient of cognitive impairments. Here, we present three tangible visual records of patients with ET who have developed dementia (Video 1, Figure 1). We do so to underscore the point that dementia is an issue for a not insignificant- number of the ET patients whom we encounter in clinical settings, and not merely an academic problem on paper. Its presence has profound prognostic import for ET patients; indeed, increasing the Clinical Dementia Rating score is associated with a 3.80-fold increased risk of mortality among ET patients.3
1 Funding: NINDS R01NS086736.
2 Financial Disclosures: None.
3 Conflicts of Interest: The authors report no conflicts of interest.
4 Ethics Statement: This study was performed in accordance with the ethical standards detailed in the Declaration of Helsinki. The authors’ institutional ethics committee has approved this study and all patients have provided written informed consent. All patients that appear on video have provided written informed consent; authorization for the videotaping and for publication of the videotape was provided.
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