Parkinson's disease and dementia with Lewy bodies: one disease or two?

Parkinson's disease (PD) and dementia with Lewy bodies (DLB) have clinical features in common and are both characterized neuropathologically by the presence of Lewy bodies (LBs). We conducted a clinicopathological correlation pilot study to better understand whether PD and DLB represent two distinct nosological entities or rather exist along the spectrum of a single LB disease. A neuropathologist blinded to clinical diagnoses evaluated brains with largely pure LB pathology to determine LB distribution and frequency. Research clinicians blinded to LB distribution and frequency determined consensus clinical diagnoses. Clinical features separated cases into two groups, one having features most compatible with PD and the other with DLB. The groups were distinguishable mainly by the time course of clinical symptoms. Although the presence of neocortical LBs was more common in the group of patients with clinical features of DLB, neocortical LBs were also present in 1 member of the PD group and even in the clinically normal control subject. Thus, there appear to be two clinical syndromes, distinguished mainly by the time course of symptoms. The mechanisms responsible for the different clinical presentations are not known, and the issue of whether PD and DLB represent two distinct diseases remains unsettled.