Summary

Dementia is a constant manifestation of Parkinson's disease; it is the third most common cause of dementia after Alzheimer's disease and stroke. The clinical manifestations are similar to those seen in other degenerative disorders that cause dementia with some minimal differences; some specific disturbances such as depression and a decline in verbal fluency may identify individuals who are in the early stages of dementia. While patients advanced in age seem to be at higher risk of dementia with Parkinson's disease, the risk is uniform throughout the duration of disease. There are no known environmental risk factors specific for dementia, though many putative factors have been identified for Parkinson's disease. There is a strong evidence to suggest a genetic etiology, but more work is essential because of the unusual relationship between Alzheimer's disease, Lewy body dementia and the dementia of Parkinson's disease.

Introduction

Nearly all of the therapeutic success in Parkinson's disease during the last three decades have been dampened by the presence of dementia which occurs as a regular manifestation. There is general agreement that dementia is most common in older patients with Parkinson's disease and that it is the single most important factor limiting treatment. Most also agree that there is a considerable overlap in clinical manifestations with Alzheimer's disease and dementia of the Lewy body type. The frequency of dementia in Parkinson's disease is even higher than appreciated (Girotti et al., 1988; Mayeux et al., 1990) and it increases the mortality rate by at least twofold compared with nondemented persons of the same age with and without Parkinson's disease (Marder et al, 1991).