Heterogeneity in Reports of Dementia Disease Duration and Severity: A Review of the Literature

BACKGROUND: The burden of dementia is changing due to population aging and changes in incidence and risk factor profiles. Reliable projections of future disease burden require accurate estimates of disease duration across different stages of dementia severity. OBJECTIVE: To provide an overview of current evidence on severity stage and disease duration in patients with dementia. METHODS: We reviewed the literature on duration of mild cognitive impairment (MCI), dementia, and various dementia severity stages. Data on study setting, country, sample size, severity stages, dementia type, and definition of disease duration was collected. Weighted averages and Q-statistics were calculated within severity stages and duration definitions. RESULTS: Of 732 screened articles, 15 reported the duration of one or more severity stages and only half of those reported severity stage onset to conversion to the following stage. In those studies, MCI, very mild dementia, and mild dementia stages lasted 3-4 years and moderate and severe dementia stages lasted 1-2 years. Information on the disease duration was reported in 93 (13%) of screened articles and varied from 1 to 17 years. Reporting of dementia severity stage and disease duration in the literature was highly heterogeneous, which was accounted for only in part by dementia type, study setting, or continent of data collection. CONCLUSION: The duration of dementia disease stages shortens with advancing stage. However, reliable modelling of future dementia burden and informing of intervention strategies will require more consistently reported duration estimates from studies that follow individuals longitudinally throughout their entire disease course.