Older U.S. adults with schizophrenia may be more likely to be diagnosed with dementia than those who do not have a serious mental illness (SMI), according to a report in JAMA Psychiatry. The study also found that this population is more likely to receive a dementia diagnosis at an earlier age.
“Approximately 28% of the group with schizophrenia had received a diagnosis of dementia before 66 years of age, indicating early-onset dementia,” wrote T. Scott Stroup, M.D., M.P.H., of Columbia University Vagelos College of Physicians and Surgeons and colleagues. “The implications of this high rate of comorbidity are substantial for families and for the service system, which must provide high levels of care for individuals with a combination of disabling conditions and uncertain treatment pathways.”
Stroup and colleagues examined Medicare data from 2007 to 2017 to estimate dementia diagnoses among people aged 66 years or older. They compared those who had received a diagnosis of schizophrenia with those without a diagnosis of schizophrenia, bipolar disorder, or recurrent major depressive disorder (that is, without SMI). Dementia was defined by the diagnostic codes used by Centers for Medicare & Medicaid Services Chronic Conditions Warehouse algorithm for Alzheimer’s disease and related disorders or senile dementia.
The study population of more than 8 million adults 66 years or older included more than 74,000 individuals with schizophrenia and more than 7.9 million without SMI. The analysis by Stroup and colleagues revealed the following:
- The prevalence of diagnosed dementia was 27.9% among individuals with schizophrenia compared with 1.3% in the group without SMI at 66 years of age. By 80 years of age, the prevalence of dementia diagnoses was 70.2% in the group with schizophrenia compared with 11.3% in the group without SMI.
- The annual incidence of dementia diagnoses per 1,000 person-years at 66 years of age was 52.5 among individuals with schizophrenia and 4.5 among individuals without SMI and increased to 216.2 and 32.3, respectively, by 80 years of age.
- The prevalence of Alzheimer’s disease diagnoses at 66 years of age was 8.2% in the group with schizophrenia and 0.4% in the group without SMI. By 80 years of age, the prevalence of Alzheimer’s diagnoses was 37.2% in the group with schizophrenia and 5.1% in the group without SMI.
The authors noted that much remains unknown about the onset, course, and management of schizophrenia in patients with dementia. “Identification of modifiable risk factors, possibly including anticholinergic medications, inadequately treated psychosis, and comorbid medical conditions such as hypertension and diabetes, may help focus prevention efforts,” they wrote.
“Further investigation is also needed of the clinical assessment of dementia in patients with schizophrenia, particularly broad neuropsychological assessment that covers the characteristic cognitive deficits of both schizophrenia and dementia and the evaluation of different medication classes for treatment and the course of illness in people with schizophrenia and dementia,” they added.
For related information, see the Psychiatric News article “Milestones in the History of Schizophrenia. A Comprehensive Chronology of Schizophrenia Research: What Do We Know and When Did We Know It.”