Time Trends in the Prevalence of Neurocognitive Disorders and Cognitive Impairment in the United States: The Effects of Disease Severity and Improved Ascertainment
Affiliations: [a]
Biodemography of Aging Research Unit, Social Science Research Institute, Duke University, Durham, NC, USA
| [b]
Department of Surgery, Duke University Medical Center, Durham, NC, USA
Correspondence:
[*]
Correspondence to: Igor Akushevich, PhD, Biodemography of Aging Research Unit, Center for Population Health and Aging, Social Science Research Institute, Duke University, 2024 W. Main Street, Durham, NC 27708, USA. Tel.: +1 919 668 2715; E-mail: igor.akushevich@duke.edu.
Abstract: Background:Trends in the prevalence of cognitive impairment (CI) based on cognitive assessment instruments are often inconsistent with those of neurocognitive disorders (ND) based on Medicare claims records. Objective:We hypothesized that improved ascertainment and resulting decrease in disease severity at the time of diagnosis are responsible for this phenomenon. Methods:Using Medicare data linked to the Health and Retirement Study (1992–2012), we performed a joint analysis of trends in CI and ND to test our hypothesis. Results:We identified two major contributors to the divergent directions in CI and ND trends: reductions in disease severity explained more than 60% of the differences between CI and ND prevalence over the study period; the remaining 40% was explained by a decrease in the fraction of undiagnosed individuals. Discussion:Improvements in the diagnoses of ND diseases were a major contributor to reported trends in ND and CI. Recent forecasts of CI and ND trends in the U.S. may be overly pessimistic.
Keywords: Alzheimer’s disease, Ascertainment, cognitive impairment, disease prevalence, Health and Retirement Study (HRS), Medicare, neurocognitive disorders, severity, Telephone Interview for Cognitive Status (TICS), time trends, underdiagnosis
