At 66 years of age, the prevalence of diagnosed dementia among individuals with schizophrenia is about 21.5 times higher than the prevalence of dementia among individuals without a serious mental illness (SMI), according to research published in JAMA Psychiatry.

To examine age-specific incidence and prevalence of dementia among adults aged 66 or more years with schizophrenia, researchers took data from national Medicare claims from 2007 through 2017. Both cohorts included only individuals aged 66 years or older with at least 1 year of continuous enrollment in fee-for-service Medicare and Part D.

Individuals with bipolar disorder or recurrent major depressive disorder were excluded from the comparison condition. Either 2 outpatient codes or 1 inpatient code during the qualifying period in any position in the diagnosis list were required to meet diagnostic criteria for schizophrenia, dementia or other SMI.

The researchers calculated prevalence and incidence of diagnosed dementia and conducted follow-up for prevalence and incidence analyses until death, end of data availability or loss of eligibility. Rates of nursing home admission within 30 and 90 days of new dementia diagnoses were also calculated in both cohorts to “examine the possibility that for individuals with schizophrenia, dementia was diagnosed to facilitate admission to nursing homes.”


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Of 8,011,733 adults (63.4% women and 36.6% men, mean age of 74 years), a group of 74,170 individuals met claims-based diagnostic criteria for schizophrenia.

The prevalence of dementia diagnoses at 66 years of age was 27.9% in the group without SMI and 1.3% in the group without SMI (21.5 times higher). By 80 years of age, the prevalence of dementia diagnoses was 70.2% in the group with schizophrenia and 11.3% in the group without SMI (6.2 times higher).

At 66 years of age, the prevalence of dementia diagnoses was 27.6% among non-Hispanic White individuals, 28.8% among Black individuals, and 28.6% among Hispanic individuals. At 80 years of age, the prevalence was 69.3% among non-Hispanic white individuals, 74.6% among Black individuals, and 67.7% among Hispanic individuals.

In a sensitivity analysis, researchers excluded cases of potentially reversible causes of dementia. In that analysis, the prevalence of dementia diagnosis in the group with schizophrenia was 23.2% at 66 years of age and 1.0% in the group without SMI. At 80 years of age, the prevalence was 61.7% in the group with schizophrenia and 9.6% in the group without SMI (6.4 times higher).

The annual incidence of dementia diagnoses per 1000 person-years at 66 years of age was 52.5 (95% confidence interval (CI), 50.1-54.9) among individuals with schizophrenia and 4.5 (95% CI, 4.4-4.6) among individuals without SMI. That 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.

Among people who were not in a nursing home at the time of their first diagnosis of dementia, 25.2% in the group with schizophrenia were admitted to a nursing home within 30 days of dementia diagnosis.

Limitations of the study included the inability to confirm diagnoses.

Disclosure: This study was supported by a grant from the National Institute of Mental Health. A few study authors declared affiliations with the pharmaceutical industry. Please see the original reference for a full list of authors’ disclosures.

References

Stroup TS, Olfson M, Huang C, et al. Age-specific prevalence and incidence of dementia diagnoses among older US adults with schizophrenia. JAMA Psychiatry. Published online March 10, 2021. doi: 10.1001/jamapsychiatry.2021.0042