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

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 <.001) overall comorbidity (58.2% vs 86.5%) and had lower prevalence rates of diabetes, obesity, and circulatory diseases; however, the prevalence rates of diseases of the nervous system in YO-AD (6.2%) were higher compared with those of patients with LO-AD (4.5%). The cluster analysis revealed a distinctive group of patients with YO-AD with either no comorbidity or with a disease of the nervous system. Endocrine, nutritional, and metabolic diseases and diseases of the circulatory system were present in 34% of the patients with YO-AD. Conclusion: Comorbidity is less common in YO-AD than in LO-AD. However, general practitioners should be aware that approximately one-third of the patients with YO-AD suffer from or have endocrine, nutritional, and metabolic diseases and/or diseases of the circulatory system. Treatment should therefore not only focus on dementia but also on comorbidity. This attention may slow the functional decline in AD. These exploratory analyses suggested a higher prevalence of nervous system diseases in YO-AD compared with LO-AD. However, the finding did not reach statistical significance and in combination with the exploratory nature of the analyses justifies further investigation. If verified, this finding may help to decrease the time to diagnosis of AD and, subsequently, support in young patients with a neurological disease. Further investigation is needed to gain more insight into the association between comorbidity and AD in younger people.