Abstract
Although the incidence of psychotic disorders among older people is substantial, little is known about the association with subsequent dementia. We aimed to examine the rate of dementia diagnosis in individuals with very late-onset schizophrenia-like psychosis (VLOSLP) compared to those without VLOSLP. Using Swedish population register data, we established a cohort of 15 409 participants with VLOSLP matched by age and calendar period to 154 090 individuals without VLOSLP. Participants were born between 1920 and 1949 and followed from their date of first International Classification of Diseases [ICD], Revisions 8-10 (ICD-8/9/10) non-affective psychotic disorder diagnosis after age 60 years old (or the same date for matched participants) until the end of follow-up (30th December 2011), emigration, death, or first recorded ICD-8/9/10 dementia diagnosis. We found a substantially higher rate of dementia in individuals with VLOSLP [hazard ratio (HR): 4.22, 95% confidence interval (95% CI) 4.05-4.41]. Median time-to-dementia-diagnosis was 75% shorter in those with VLOSLP (time ratio: 0.25, 95% CI 0.24-0.26). This association was strongest in the first year following VLOSLP diagnosis, and attenuated over time, although dementia rates remained higher in participants with VLOSLP for up to 20 years of follow-up. This association remained after accounting for potential misdiagnosis (2-year washout HR: 2.22, 95% CI 2.10-2.36), ascertainment bias (HR: 2.89, 95% CI 2.75-3.04), and differing mortality patterns between groups (subdistribution HR: 2.89, 95% CI 2.77-3.03). Our findings demonstrate that individuals with VLOSLP represent a high-risk group for subsequent dementia. This may be due to early prodromal changes for some individuals, highlighting the importance of ongoing symptom monitoring in people with VLOSLP.
Highlights
The incidence of psychotic disorders among older people is substantial, little is known about the association with subsequent dementia
Association between very late-onset schizophrenia-like psychosis (VLOSLP) and subsequent dementia In Cox regression models, compared with the non-VLOSLP group, we found a higher rate of dementia in participants with VLOSLP [fully adjusted hazard ratio (HR): 4.22, 95% confidence interval (95%CI) 4.05–4.41; Table 2], after adjustment for sex, education level, disposable income, region of birth and family liability for psychotic disorder
There was evidence of nonproportional hazards for the VLOSLP exposure, but not for other covariates. Further exploration of this issue (Fig. 1) suggested that the dementia HR associated with VLOSLP was highest in the first year after VLOSLP diagnosis, rates of dementia remained higher in the VLOSLP group for up to 20 years of follow-up
Summary
The incidence of psychotic disorders among older people is substantial, little is known about the association with subsequent dementia. Non-affective psychotic disorders typically have their first onset in adolescence or early adulthood (Kessler et al, 2007), recent population-based evidence suggests a second peak of incidence after 60 years old, in women (Stafford, Howard, & Kirkbride, 2018; Stafford, Howard, Dalman, & Kirkbride, 2019) This is referred to as very late-onset schizophrenia-like psychosis (VLOSLP) in those aged over 60 years old (Howard, Rabins, Seeman, & Jeste, 2000). Long follow-up periods are required to fully characterise the relationship between VLOSLP and dementia and reduce the risk of protopathic bias
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