Essential Tremor in the Elderly and Risk for Dementia

The objective is to examine the risk of dementia in subjects with essential tremor (ET) involved in the Arizona Study of Aging and Neurodegenerative Disorders. All subjects were free of a neurodegenerative diagnosis at baseline and had annual motor, general neurological, and neuropsychological assessments. Subjects with ET were compared with controls for the risk of dementia. There were 83 subjects with ET and 424 subjects without tremor. Mean age at study entry was for ET and for controls. Median tremor duration was 5.2 years at study entry. Followup was a median of 5.4 years (range 0.9 to 12.1). The hazard ratio for the association between ET and dementia was 0.79 (95% CI 0.33 to 1.85). The hazard ratio for the association between tremor onset at age 65 or over, versus onset before age 65, was 2.1 (95% CI 0.24 to 18) and the hazard ratio for the association between tremor duration greater than 5 years, versus less than 5 years, was 0.46 (95% CI 0.08 to 2.6). We conclude that all elderly ET was not associated with an increased risk of dementia but that a subset of subjects with older age onset/shorter duration tremor may be at higher risk. 1. Introduction Essential tremor (ET) is a common neurological condition which increases with the age of the population and contributes to significant disability in most affected patients. Previous cross-sectional studies have shown that patients with ET may have minor cognitive deficits on formal testing although most of these older studies have been done with advanced ET patients being assessed for deep brain stimulation as treatment for tremor [1, 2]. More recently, a population study of ET demonstrated that more mildly affected, largely untreated ET individuals may be more likely to complain of memory problems and have deficits at testing [3]. This same population was more likely to have prevalent dementia, largely driven by elderly onset ET [4]. In those nondemented at baseline, incident dementia was greater in ET [5]. This study seeks to compare the risk of developing dementia in subjects with ET versus controls without tremor in a large, well-categorized cohort of individuals involved in a longitudinal aging study, the Arizona Study of Aging and Neurodegenerative Disorders (AZSAND). 2. Methods Participants without dementia or another neurodegenerative disorder at study entry and who had at least one follow-up visit were selected from the 23 May 2013 version of the AZSAND database which included 3300 subjects. All participants, both cases and controls, were initially recruited into the study largely as a result