Rate of cognitive decline during the premotor phase of essential tremor: A prospective study

Objective: To characterize the rate of cognitive decline during the premotor phase of essential tremor (ET) in comparison to prevalent ET cases and controls. Methods: In this population-based, prospective study of people aged 65 years and older (Neurological Disorders in Central Spain), a 37-item version of the Mini-Mental State Examination was administered at 2 visits (baseline and follow-up, approximately 3 years later). We compared the rate of cognitive decline in 3 groups: prevalent ET cases (i.e., participants diagnosed with ET at baseline and at follow-up), "premotor" ET cases (i.e., participants diagnosed with incident ET at follow-up, but not at baseline), and controls (i.e., participants not diagnosed with ET at baseline or follow-up). Results: The 2,375 participants included 135 prevalent ET cases, 56 premotor ET cases, and 2,184 controls. During the follow-up period of 3.4 6 0.5 years (mean 6 SD), the 37-item version of the Mini-Mental State Examination declined by 0.7 6 3.3 points (0.2 6 1.0 points/year) in prevalent ET cases, 1.1 6 3.5 points (0.3 6 1.0 points/year) in premotor ET cases, and 0.1 6 3.9 points (0.0 6 1.2 points/year) in controls (p 5 0.014). The difference between premotor ET cases and controls was significant (p 5 0.046), as was the difference between prevalent ET cases and controls (p 5 0.027). Conclusions: In this prospective cohort, cognitive test scores in premotor and prevalent ET cases declined at a faster rate than in elders without this disease. A decline in global cognitive function may occur in a premotor phase of ET.