Faster rate of cognitive decline in essential tremor cases than controls: a prospective study

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Abstract
Background: Mild cognitive deficits have been reported in essential tremor (ET). However, these cognitive deficits have been assessed in cross‐sectional rather than longitudinal analyses. Objective: To determine whether decline in cognitive test scores occurs at a faster rate in ET cases than controls. Methods: In a population‐based study of older people (≥ 65 years) in central Spain (Neurological Disorders in Central Spain, NEDICES), non‐demented ET cases and controls were followed prospectively. Participants with baseline or incident Parkinson’s disease or dementia were excluded as were participants who developed incident ET. At baseline (1994–1995) and at follow‐up (1997–1998), a 37‐item version of the mini‐mental state examination (37‐MMSE) was administered. Results: A total of 2319 participants (72.4 ± 5.8 years) included 135 prevalent ET cases and 2184 controls. At baseline, the mean 37‐MMSE in cases was 28.8 ± 5.8 vs. 30.2 ± 4.8 in controls (P = 0.02). During the 3‐year follow‐up period, the 37‐MMSE declined by 0.70 ± 3.2 points in cases vs. 0.11 ± 3.8 points in controls (P = 0.03). In analyses that adjusted for age, education, and other potential confounders, the case–control difference remained robust. Discussion: In this population‐based, prospective study of non‐demented elders, baseline cognitive test scores were lower in ET cases than controls; moreover, during the 3‐year follow‐up period, these scores declined at a rate that was seven‐times faster in ET cases. This study provides evidence that cognitive deficits in ET are not static, and they appear to be progressing at a faster rate than in elders without this disease.