People with schizophrenia and other primary psychotic disorders are known to have elevated dementia risk, but the size of that risk has been unclear and the population is easily lost between psychiatric and geriatric services. This review synthesised prevalence and incidence data through meta-analysis and narrative synthesis.
Pooled dementia prevalence in older adults with psychotic disorders was 24.3% (95% CI 20.5-28.5), after excluding one outlier, with substantial heterogeneity (I-squared 84.7%). Incidence estimates varied too widely to pool meaningfully. Heterogeneity was driven by the type of prevalence measured, care setting, geographical region and age.
About one in four is high enough to change expectations in clinic, and the practical difficulty is diagnostic rather than epidemiological. Cognitive impairment is intrinsic to long-standing schizophrenia, antipsychotics have anticholinergic and sedative effects, and negative symptoms overlap with the presentation of dementia — so distinguishing superimposed dementia from the illness and its treatment is genuinely hard. The value of this figure is that it raises the prior: in an older patient with a psychotic disorder and functional decline, dementia is a common explanation rather than a remote one, and worth assessing for properly rather than attributing to the primary illness.
- Pooled dementia prevalence 24.3% in older adults with psychotic disorders
- High heterogeneity (I-squared 84.7%); incidence too variable to pool
- Cognitive impairment intrinsic to schizophrenia complicates diagnosis
- In functional decline, assess for dementia rather than attributing to the illness
The statistics, in plain English
An I-squared of 84.7% means the studies disagreed considerably, so 24.3% is a central estimate across quite different populations and settings rather than a figure to quote precisely. That one outlier had to be excluded to reach it is worth noting too. The direction — substantially elevated compared with the general older population — is secure; the exact proportion is not.
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