Survival of patients with incident dementia who had a pre-existing psychiatric disorder: a population-based 7-year follow-up study

Objectives: Although it is widely accepted that psychiatric disorders and dementia coexist and survival data for dementia patients have been published, there is a paucity of information regarding the survival of patients with a psychiatric disorder who develop dementia. This study fills this information gap providing survival data on patients with such comorbidity and identifies mortality risk factors.

Methods: All residents of Saskatchewan, a Canadian province, diagnosed with psychiatric problems and/or dispensed a psychiatric drug in 2000 and without dementia were followed through to 31 December 2006; the development of incident dementia was noted. Median survival time (in months) and selected predictors of mortality were measured. Analyses used Cox's proportional hazard model. Incidence density of dementia for the year 2000 was also computed.

Results: By December 2006, 5,583 subjects with psychiatric disorders in 2000 had been diagnosed with incident dementia, and 60.65% of them died. Dementia-incidence density in this population for 2000 was 0.01 per 1000 person years at risk among those aged 18-64 years and rapidly increased to 3.13 per 1000 person years at risk among those aged 75 to 84 years. The median survival time from dementia onset to death was 32.66 months (interquartile range 31.21-34.14). Being male, later age of onset of dementia, having a lower income, and a high chronic disease score predicted shorter survival.

Conclusions: The comorbidity of psychiatric disorders and dementia resulted in shorter survival compared with that reported for patients with dementia only. These findings can be used for prognosis for patients, caregivers, and service providers.