Parkinson's disease, cognition and aging Clinical, neuropsychological, electrophysiological and cranial computerized tomographic assessment

Abstract

Forty-three patients with Parkinson's disease (PD) and thirty-seven normal volunteers were subjected to clinical, neuropsychological, neurophysiological (P300 component of the event-related potentials ERP) and radiological (cranial computerized tomographic scanning CCT) evaluation. Intentional memory was more impaired in PD than in normal controls, more so in the demented group of patients, and was related to enlargement of third ventricular size in CCT. While intentional memory was age related in PD patients, perception was age-related in normal controls. Neither global nor specific cognitive functions were related to duration, severity of parkinsonian motor disability, or depression. However, depression in PD was significantly related to parkinsonian motor disability. P300 latency was more prolonged in PD patients than normal controls. P300 parameters of PD patients were not influenced by age, cognitive functions, duration or severity of motor disability, or depression. The reaction time was the only P300 parameter that was age-related in normal controls. Subcortical atrophy as indicated by CCT was more marked in PD and correlated with age in both patients and controls. Subcortical atrophy was significantly related to cognitive functions in PD but not in normal controls. It was concluded that cognitive impairment in PD could be attributed to complex cognitive changes rather than age. It is a disease process, though not directly related to parkinsonian motor disability or depression. PD differed from normal aging as regards the effect of age on the specific cognitive functions, where in PD patients, age was related to intentional memory, yet in normal controls, it was related to perception. Intentional memory deterioration was found to be specific of PD, being related to subcortical atrophy as well as being more pronounced in the demented group of patients.

Introduction

The occurrence of cognitive impairment in Parkinson's disease (PD) as the disease progressed was frequently reported (Charcot and Vulpian, 1861; Charcot, 1875; Mjones, 1949; Walshe, 1955; Reitan and Boll, 1971; Shaw et al., 1980).

This cognitive impairment could be either global or specifically involving certain aspects such as visual discrimination, visuospatial orientation, verbal fluency, memory, frontal lobe functions and conceptual abilities (Girotti et al., 1988).

The frequency of cognitive impairment increases with increased duration of the disease and severity of motor disability, and has been attributed to the possible role of advancing age (Dubois et al., 1990).

Whereas dementia in PD ranged from 10 to 40% (Girotti et al., 1988; Mayeux et al., 1990), depression, mild or moderate, occurred in 40% (Hamilton, 1960). However, 25% experienced depression before motor symptoms of PD became manifest, associated later with mild intellectual dysfunction (Starkstein et al., 1992).

Impairment in intellectual functions involved mainly complex language comprehension, visuospatial factors and attention in parkinsonian patients with the highest depression levels (Vilert et al., 1991).

The aim of this work was to evaluate the influence of aging on the cognitive domain in PD and to assess points of similarities as well as differences between PD and normal aging. It was hoped that this study would clarify whether such changes were specifically due to the disease process of PD or to an underlying age process, and to clarify the relationship between cognitive decline in PD and parkinsonian motor disability or depression.