Dementia in dementia with Lewy bodies may not be attributable to Alzheimer pathology

We read with interest the report by Gilman and colleagues concerning the use of [C]dihydrotetrabenazine positron emission tomography (PET) to differentiate dementia with Lewy bodies (DLB) from Alzheimer’s disease (AD). We do, however, have some concerns regarding their use of terminology. The authors divide DLB into those patients with dementia preceding or starting at the same time as their movement disorder, which they term DLB-AD, and those in which parkinsonism preceded the dementia, which they term DLBPD. The term DLB-AD implies that the dementia in DLB is attributable or inevitably linked to Alzheimer’s disease. Although a degree of Alzheimer pathology often accompanies DLB, genetic studies demonstrate that dementia in Lewy body Parkinson’s disease may occur in the absence of Alzheimer pathology, and Alzheimer pathology is not always seen in sporadic DLB: it is notable that in the one case of DLB-AD coming to postmortem in Gilman and colleagues’ study, no AD pathology was found. The consensus criteria for the diagnosis of DLB arbitrarily determine that patients in whom dementia is unaccompanied by parkinsonism for the first year be diagnosed with DLB and those in whom motor features occur after the first year as having Parkinson’s disease dementia (PDD). It is likely that these diseases are on a continuum, a hypothesis that maybe supported by the similar PET findings in both DLB-AD and DLB-PD reported by Gilman and colleagues. Although the terms PDD and DLB may be imperfect, we suggest that they may cause less confusion than the terms DLB-PD and DLB-AD.