No Significant Difference in Cognitive Decline and Mortality between Parkinson's Disease Dementia and Dementia with Lewy Bodies: Naturalistic Longitudinal Data from the Swedish Dementia Registry

Background: Whether dementia with Lewy bodies (DLB) and Parkinson's disease dementia (PDD) are distinct disorders or two subtypes of the same entity, is not yet fully understood. There is a dearth of knowledge on differences in longitudinal clinical outcomes between DLB and PDD. Objective: We aimed to compare longitudinal trend of cognitive decline, mortality, and their determinant factors between patients with DLB and PDD. Methods: At baseline, we recruited 1110 DLB, and 764 PDD patients registered in the Swedish dementia registry (SveDem) during 2007-2015. Cognitive status was assessed at baseline and each follow-up visit by mini-mental state examination (MMSE). At least one follow-up MMSE was available for 411 (37.0%) DLB and 229 (30.0%) PDD patients. Rate of cognitive decline and mortality risk were compared between the two groups. Results: After an average of 2-years, the rate of cognitive decline did not differ between DLB (1.1 MMSE unit/year) and PDD (1.2 MMSE unit/year) groups (p = 0.970). There was no significant difference in the median survival time between DLB (4.0 years) and PDD (4.1 years) groups (Log rank p = 0.614). Antipsychotic drug use in DLB and larger number of medications in PDD were the most important determinants of faster annual cognitive decline. Conclusions: Our findings from real-world clinical practice demonstrated that the rate of cognitive decline and mortality do not differ significantly between DLB and PDD at least over 2 years, yet, various factors might determine clinical outcome in these two groups. It seems that DLB and PDD are probably similar synucleinopathies, with phenotypical variations in the order of manifestations rather than course of progression and clinical outcome.