Estimates of Incidence and Prevalence of Conversions to Mild Cognitive Impairment and Dementia in Patients With Essential Tremor.

BACKGROUND AND

OBJECTIVES

It is increasingly recognized that cognitive decline is a feature of essential tremor (ET). However, studies of the prevalence, incidence, and annual conversion proportions to mild cognitive impairment (MCI) and dementia are based on limited data, and results are heterogeneous.

METHODS

Older individuals with ET were enrolled in a prospective longitudinal study of cognitive function. Recruitment was national, and participants resided in 43 states. Extensive neuropsychological testing was conducted during home visits at baseline and again during follow-up visits at 18, 36, 56, 72, and 90 months (M years of observation = 4.7 years, maximum = 7.5 years). Participants were assigned a cognitive diagnosis of normal cognition (NC), MCI, or dementia by expert consensus based on the detailed assessments conducted during each visit. Prevalence, incidence, and annual conversion proportions to MCI and dementia were calculated. We also performed a systematic review of the relevant literature followed by a meta-analysis to derive pooled estimates of prevalence, incidence, and annual conversion proportions for comparison purposes.

RESULTS

There were 350 participants, M baseline age = 79.6 years, 60.6% female. Cumulative prevalences of MCI and dementia were 22.0% (95% confidence interval [CI] = 18.0-26.6) and 14.6% (95% CI = 11.3-18.7), cumulative incidences were 12.9% (95% CI = 9.3-17.6) and 10.2% (95% CI = 7.2-14.2), respectively, and the average annual proportion of conversions from MCI to dementia was 13.8%. Pooled estimates of these values were derived from meta-analyses of our data and existing studies of ET cohorts, general population cohorts, and Parkinson disease (PD) cohorts. The burden of MCI and dementia in ET was overall substantially higher than that observed in the general population yet lower than that seen in PD.

DISCUSSION: The data document the longitudinal trajectory of cognitive impairment in ET in the largest available sample to date. Whether considered as stand-alone results, or when combined with data from the extant literature, the occurrence of MCI and dementia in ET is higher than observed in same age members of the general population, but is less pronounced than observed in same aged individuals with PD.