Dementia in long-term Parkinson's Disease patients receving chronic levodopa therapy

Abstract

The present study investigated the hypothesis that two subgroups of Parkinson's Disease patients may exist: those susceptible to dementia and those resistant to dementia. The sample comprised 43 white patients (26 males and 17 females), all receiving levodopa therapy. Cognitive functioning was assessed using subtests from the WAIS and abbreviated scales from Liria's Neuro-psychological Investigation. Three cognitive components, namely general intellectual functioning, memory span and linguistic skills, emerged from a principal component analysis of the test scores. Uni-dimensional and multi-dimensional cluster analytic investigations of the component scores failed to demonstrate the existence of patient subgroups. The cognitive functioning of the patient sample was characterised by a continuous distribution with the demented patients representing the severely impaired extreme. The influence of five patient variables on cognitive functioning in Parkinson's Disease was examined using stepwise multiple regression analyses. Present age, age at onset, duration of illness, depression and sex acted as predictor variables. The three time-related variables emerged as important determinants of dementia but, because of their high intercorrelation, their individual influences were difficult to establish. The influences of depression and sex proved to be negligible. The findings of the present study were reviewed against the background of recent histopathological evidence of the involvement of both subcortical and cortical brain structures in the Parkinson's Disease process.