Academic journal article Hong Kong Journal of Psychiatry

Research into Parkinson's Disease and Its Relevance to Understanding Degenerative Neurological Disease

Academic journal article Hong Kong Journal of Psychiatry

Research into Parkinson's Disease and Its Relevance to Understanding Degenerative Neurological Disease

Article excerpt

Abstract

Although Parkinson's disease has been regarded primarily as a disorder of movement, there is evidence that a substantial proportion of sufferers also show impairment of cognitive function. The relationship between disordered movement and impaired cognitive function is of great clinical and theoretical importance. We have sought to clarify this relationship in the context of our own and other research. Our current study is a prospective comparison of cognitive function in patients with Parkinson's disease and a matched control group, of 15 years duration.

DSM III R diagnosis of dementia has been identified in a substantial proportion of the patients with Parkinson's disease but none of the control group. Further, patients with Parkinson's disease and some of the control group have shown lesser degrees of impairment. These findings demonstrate that dementia in patients with Parkinson's disease is not due to a coincident disease and that 'subcortical dementia' is not the sole cause of cognitive decline. The results are compatible with the notion that dementia in patients with Parkinson's disease is due to an interaction between a specific pathology and the loss of neuronal cells as a part of the ageing process.

Key words: Parkinson's disease, Dementia, Neurodegenerative disease

Introduction

Parkinson's disease (PD) has attracted the interest of psychiatrists for 2 reasons--first, the management of psychiatric complications of PD is clinically important and, second, the study of the disease gives insight into a range of psychiatric and neurological disorders.

As a trainee in psychiatry, I prepared a dissertation based on a retrospective study of the psychiatric syndromes associated with PD. (1) This experience led to an interest in PD, which has continued throughout my professional life. Research projects on various aspects of PD followed: the effects of levodopa on the mood of patients receiving treatment for PD; (2) cognitive impairment in PD; (3) the effects of PD on driving skills; (4) emotional lability in PD; (5) facial expression in PD; (6) and factors influencing survival in PD. (7) Currently, work concerns cognitive impairment in PD and the methodological issues encountered in research into this field. (8) This work has some relevance to the wider understanding of neurodegenerative disease and the story of the evolution of thinking in this field is both interesting and instructive. (9)

Current Research

Our current research is a prospective controlled study of the incidence of dementia in PD. Since 1985, a trial has included a group of 50 patients with PD and a control group of 50 people. PD was diagnosed using the UK Brain Bank Criteria. (9) Controls were matched for age, sex, and premorbid intelligence. All patients were free of other major physical illness and all were assessed at intervals of approximately 9 months using a series of tests of intellectual function, premorbid intelligence, disability, severity of neurological symptoms, and mood. The diagnosis of dementia was made by the rigorous application of DSM III R criteria by blind raters and the results analysed by survival analysis. (9)

Of 83 subjects in whom a diagnosis of PD was sustained and who did not show dementia at the first assessment and 50 control subjects, 21 patients with PD and no control subjects have reached the criteria for dementia during a period of 12 years. A further 21 patients with PD and 8 control subjects have shown lesser degrees of cognitive impairment. The incidence of dementia in PD can be expressed as 46.9/1000 person years of observation. Age at entry to the study, age at onset of PD, duration of PD, and severity of PD were positively associated with the occurrence of dementia. (9) These findings are consistent with our earlier findings (10-11) and echo the findings of studies from other parts of the world. (9)

Causes of Cognitive Impairment in Parkinson's Disease

During the past 35 years, the relationship between severe cognitive impairment and PD has been considered in 3 distinct ways--first, that the decline is due to a coincidental dementing illness such as Alzheimer's disease (AD), second, that it is the product of changes in the subcortical region of the brain in which both motor and cognitive functions are disturbed, and third, that it is the result of interactions between the pathological processes which occur in PD and other processes which lead to the death of brain cells of which age-related cell degeneration is the most important. …

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