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Serial assessments of cognition, mood, and disability were carried out at nine month intervals over a 54 month period on a cohort of 87 patients with Parkinson's disease (PD) and a matched cohort of 50 control subjects. Dementia was diagnosed from data by rigorously applying DSM-III-R criteria. Initially, 6% (5187) PD patients were demented, compared with none of the 50 control subjects. A further 10 PD patients met the dementia criteria during the follow up period; this was equivalent, with survival analysis, to a cumulative incidence of 190%.. With the number of person years of observation as the denominator, the incidence was 47*6I1000 person years of observation.None of the control subjects fulfilled dementia criteria during the follow up period. The Serial assessments of patients can overcome these difficulties. Firstly, poor performance on cognitive testing on a single occasion may be seen to be transient, in which case dementia is unlikely to be the cause. Secondly, decline can be directly observed rather than inferred from the use of unvalidated tests of premorbid intelligence. Thirdly, cross sectional assessment can give only an estimate of prevalence of dementia in PD but serial assessments can enable the incidence of dementia to be estimated and may provide information about the evolution and prognosis of dementia in PD.Mayeux et al recently estimated the incidence of dementia in PD.'0 They rightly emphasised that incidence is a better indicator than prevalence of the occurrence of dementia in PD: if coincident PD and dementia result in a greater mortality than PD uncomplicated by dementia the prevalence of dementia in PD will be lowered. We carried out longitudinal assessments of cognition, mood, and disability at nine month intervals over a 54 month follow up period on a cohort of patients with PD and a matched cohort of control subjects. On the basis of the data we judged whether DSM-III-R dementia was present in each subject and, if present, when it occurred. We present our findings in the form of a survival analysis.

Patients with Parkinson's disease (PD) and matched control subjects were photographed posing a range of facial expressions. The same subjects were later asked to identify the posed expressions of the other subjects. They were also asked to rate the quality of expressions posed by the control subjects after being told what each expression was. Expressions posed by healthy control subjects were more readily identifiable than expressions posed by Parkinson's patients, but the two groups did not differ in their ability to recognize facial expressions or in the goodness ratings they gave, and their error patterns were closely similar. There was no significant difference between the groups on other tests of face processing or on ratings of emotionality except for greater reported anxiety in the Parkinson's patients. We conclude that although patients with PD have reduced facial expressiveness, there is no apparent diminution in their comprehension of facial expressions or their day-to-day experience of emotion.

SYNOPSISThe performance of 47 patients with Parkinson's disease on a battery of tests of cognition, motor function, disability and mood was compared with the performance of 47 healthy control subjects who were matched to the patients on the basis of age, sex and pre-morbid IQ. An increased prevalence of impairment over a range of cognitive functions was observed in the Parkinson's disease patients as compared with their matched controls. The differences between the Parkinson's disease patients and controls could not be accounted for by factors such as depressed mood, effects of medication or motor impairment. Our findings are discussed in relation to the methodology of previous studies in this area and to the need for a comprehensive clinico-pathological longitudinal study.

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