Dementia in Parkinson's disease. 
Estimates of the prevalence of dementia in patients with Parkinson's disease (PD) vary considerably.  Dementia in PD has been linked to a visuospatial disturbance, impairment of memory, and depression.  Previous research suggests that visuospatial deficits and depression do not vary with severity of intellectual decline and thus are not useful measures to distinguish demented from nondemented patients.  We examined immediate, recent, and remote memory in patients with PD and found that unlike visuospatial performance and depression, a qualitatively distinct pattern emerged, which did vary with severity of intellectual decline.