Long-term cognitive outcome of Alzheimer's disease and dementia with Lewy bodies: dual disease is worse

Background: Longitudinal studies of dementia with Lewy bodies (DLB) are rare. Clinically, DLB is usually considered to worsen into Alzheimer's disease (AD). The aim of our study was to compare the rate of the cognitive decline in DLB, AD, and the association of the two diseases (AD + DLB). Methods: Using the Regional Network for Diagnostic Aid and Management of Patients with Cognitive Impairment database, which includes all the patients seen at all memory clinics (medical consultation and day hospitals) in four French regions, and beta regression, we compared the longitudinal the Mini-Mental State Examination scores of 1159 patients with AD (n = 1000), DLB (n = 131) and AD + DLB (association of the two) (n = 28) during follow-up of at least 4 years. Results: The mean follow-up of the patients was 5.88 years. Using beta regression without propensity scores, the comparison of the decline of patients with AD and patients with DLB did not show a significant difference, but the decline of patients with AD + DLB was worse than that of either patients with DLB (P = 0.006) or patients with AD (P < 0.001). Using beta regression weighted by a propensity score, comparison of patients with AD and patients with DLB showed a faster decline for patients with DLB (P < 0.001). The comparison of the decline of patients with AD + DLB with that of patients with DLB (P < 0.001) and patients with AD (P < 0.001) showed that the decline was clearly worse in the patients with dual disease. Conclusions: Whatever the analysis, the rate of decline is faster in patients with AD + DLB dual disease. The identification of such patients is important to enable clinicians to optimise treatment and care and to better inform and help patients and caregivers.