Point of view: Dementia in Parkinson's disease

Abstract

The prevalence of dementia in Parkinson's disease (PD) was analyzed in eight reports from peer-reviewed journals. Each report examined at least 100 patients, the period covered being 1966 to 1996. Among 1907 patients, 513,27%, were demented. The prevalence of dementia was similar in prospective and retrospective reports, and in clinic- and community-based reports. Demented patients were older than non-demented patients: 70.3 yr versus 64.3 yr. Disease duration was similar in demented and non-demented patients: 7.7 yr versus 7.9 yr. The incidence of dementia in PD was calculated from two prospective community-based reports and one retrospective clinic-based report. For the age range 55 to 64 yr, the incidence is 2.7 patients per 100 patients per year (2.7% per year). For the age range 70 to 79 yr, the incidence increased to 13.7%. For the age range 80 + yr, the incidence is 9.3%. The pathology of PD dementia was analyzed in 15 reports, each report examined at least 10 patients. Among 412 demented patients, 28%, had a pathology characterized primarily by Lewy bodies (Lbs) and 40% of the patients with Lbs (10% of all demented PD patients), had subcortical changes, only 60% of the patients with Lbs (17% of all demented PD patients), had subcortical and cortical Lbs. Among the 412 demented patients, 72%, the pathology consisted of subcortical Lbs and cortical AD changes: plaques and neurofibrillary tangles (nfts). Some of these patients also had cortical Lbs. It is postulated there are two types of PD dementia, and by inference two types of PD. One type, which may include familial PD, is characterized by cortical Lbs. The second, related to AD, or frontotemporal dementia (FTD), is characterized by cortical senile plaques and nfts. As 90% of demented PD patients have cortical changes, it is argued that PD dementia should be referred to as a cortical not a subcortical dementia.