Prevalence of Comorbidity in Patients With Young-Onset Alzheimer Disease Compared With Late-Onset: A Comparative Cohort Study

Abstract Objectives With the lack of a cure for Alzheimer disease (AD), the identification of comorbidity is important to reduce the possibility of excess disability. Although comorbidity in patients with late-onset AD (LO-AD) is common, for people with young-onset AD (YO-AD), it is unclear how often comorbidity occurs. Furthermore, it is uncertain whether comorbidity in patients with YO-AD differs from that in patients with LO-AD. The aim of this study was to explore the prevalence, types of morbidity, and morbidity profiles in patients with YO-AD compared with those of patients with LO-AD. Design Explorative cohort study from 2 separate Dutch cohorts (Needs in Young-onset Dementia [NeedYD] and the Clinical Course of Cognition and Comorbidity–Dementia Study [4C-Dementia study]). Setting Participants were recruited in 2007 and 2008 from (1) the memory clinics of 3 Dutch Alzheimer centers, (2) the memory clinics of general hospitals, (3) mental health services in the southern part of the Netherlands, and (4) young-onset dementia specialized day care facilities. A comparison group of community-dwelling, elderly patients with AD was selected from the 4C-Dementia study. Patients in this study were recruited in 2010 and 2011 from the aforementioned Alzheimer centers. Measurements The prevalence rates of comorbidity were compared between 177 patients with YO-AD and 155 patients with LO-AD. Comorbidity was classified using the International Classification of Diseases, 10th Revision (ICD-10). The total amount of comorbidity was established by counting the number of existing diseases (ICD categories or chapters) and comorbidity was also dichotomized as present or absent. Furthermore, a hierarchical cluster analysis was performed to study clusters of comorbidity. Results Compared with LO-AD, patients with YO-AD showed less ( P