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Original Investigation
March 10, 2021

Age-Specific Prevalence and Incidence of Dementia Diagnoses Among Older US Adults With Schizophrenia

Author Affiliations
  • 1Department of Psychiatry, Columbia University Vagelos College of Physicians and Surgeons, New York, New York
  • 2New York State Psychiatric Institute, New York
  • 3Institute for Health, Health Care Policy and Aging, Rutgers University, New Brunswick, New Jersey
JAMA Psychiatry. 2021;78(6):632-641. doi:10.1001/jamapsychiatry.2021.0042
Key Points

Question  What are the age-specific incidence and prevalence of dementia among older US adults with schizophrenia?

Findings  In this cohort study of 8 011 773 individuals in a national Medicare database from 2007 to 2017, at 66 years of age, 27.9% of individuals with schizophrenia also had a dementia diagnosis compared with 1.3% of individuals without a serious mental illness. The prevalence of dementia diagnoses among people with schizophrenia at 66 years of age was similar to the prevalence at 88 years of age for the group without serious mental illness.

Meaning  The findings suggest that further study is needed about the processes and impairments that lead to dementia diagnoses in patients with schizophrenia as well as prevention and treatment strategies.

Abstract

Importance  People with schizophrenia are at high risk of receiving a diagnosis of dementia. Understanding the magnitude and timing of this increased risk has important implications for practice and policy.

Objective  To estimate the age-specific incidence and prevalence of dementia diagnoses among older US adults with schizophrenia and in a comparison group without serious mental illness (SMI).

Design, Setting, and Participants  This retrospective cohort study used a 50% random national sample of Medicare beneficiaries 66 years or older with fee-for-service plans and Part D prescription drug coverage from January 1, 2007, to December 31, 2017. The cohort with schizophrenia included adults with at least 12 months of continuous enrollment in fee-for-service Medicare and Part D and at least 2 outpatient claims or at least 1 inpatient claim for schizophrenia during the qualifying years. The comparison group included adults with at least 12 months of continuous enrollment in fee-for-service Medicare and Part D and without a diagnosis of schizophrenia, bipolar disorder, or recurrent major depressive disorder during the qualifying year. Data were analyzed from January 1 to July 31, 2020.

Main Outcomes and Measures  Dementia was defined using the Centers for Medicare & Medicaid Services Chronic Conditions Warehouse diagnosis codes for Alzheimer disease and related disorders or senile dementia. Incident diagnoses were defined by at least 12 consecutive eligible months without a qualifying code before meeting dementia criteria.

Results  The study population of 8 011 773 adults 66 years or older (63.4% women; mean [SD] age, 74.0 [8.2] years) included 74 170 individuals with a diagnosis of schizophrenia (56.6% women) and 7 937 603 without an SMI diagnosis (63.5% women) who contributed 336 814 and 55 499 543 person-years of follow-up, respectively. At 66 years of age, the prevalence of diagnosed dementia was 27.9% (17 640 of 63 287) among individuals with schizophrenia compared with 1.3% (31 295 of 2 389 512) in the group without SMI. By 80 years of age, the prevalence of dementia diagnoses was 70.2% (2011 of 2866) in the group with schizophrenia and 11.3% (242 094 of 2 134 602) in the group without SMI. The annual incidence of dementia diagnoses per 1000 person-years at 66 years of age was 52.5 (95% CI, 50.1-54.9) among individuals with schizophrenia and 4.5 (95% CI, 4.4-4.6) among individuals without SMI and increased to 216.2 (95% CI, 179.9-252.6) and 32.3 (95% CI, 32.0-32.6), respectively, by 80 years of age.

Conclusions and Relevance  In this cohort study, compared with older adults without SMI, those with schizophrenia had increased risk of receiving a diagnosis of dementia across a wide age range, possibly because of cognitive and functional deterioration related to schizophrenia or factors contributing to other types of dementia. High rates of dementia among adults with schizophrenia have implications for the course of illness, treatment, and service use.

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