The Incidence of Recorded Delirium Episodes Before and After Dementia Diagnosis: Differences Between Dementia With Lewy Bodies and Alzheimer's Disease

Objectives To describe the incidence of delirium recording before and after a diagnosis of dementia is established in patients with dementia with Lewy bodies (DLB) and compare findings to a matched cohort of patients with Alzheimer's disease (AD). 
Design Retrospective cohort study. Setting and participants A cohort of patients with dementia from a large mental health and dementia care database in South London, linked to hospitalization and mortality data. We identified 194 patients with DLB and 1:4 matched these with 776 patients diagnosed with AD on age, gender, and cognitive status. 
Measures We identified delirium episodes recorded in mental health and hospital records from 1 year before to 1 year after dementia diagnosis. Using dementia diagnosis as an index date we additionally followed patients until first episode of delirium, death or a censoring point without restricting the observation period. 
Results Patients with DLB had significantly more episodes of delirium recorded in the year before dementia diagnosis than patients with AD (incidence rate 17.6 vs 3.2 per 100 person-years; P < .001). Whereas the incidence of recording of delirium episodes reduced substantially in patients with DLB after dementia diagnosis, it remained significantly higher than in patients with AD (incidence rate 6.2 vs 2.3 per 100 person-years; P = .032). Cox regression models indicate that patients with DLB remain at a higher risk of delirium than patients with AD after a dementia diagnosis.
Conclusions/Relevance Establishing a diagnosis of dementia reduces episodes classified as delirium in patients with DLB and might lead to fewer potentially harmful interventions such as hospitalization or use of antipsychotic medication.