Background: The relation between dementia with Lewy bodies (DLB) and Parkinson's disease with dementia (PDD) is unknown.
Objectives: To compare the cognitive profiles of patients with DLB and PDD, and compare those with the performance of patients with a subcortical dementia (progressive supranuclear palsy) and a cortical dementia (Alzheimer's disease).
Design: Survey of cognitive features.
Setting: General community in Rogaland county, Norway, and a university dementia and movement disorder research centre in the USA.
Patients: 60 patients with DLB, 35 with PDD, 49 with progressive supranuclear palsy, and 29 with Alzheimer's disease, diagnosed by either standardised clinical procedures and criteria (all PDD and Alzheimer cases and 76% of cases of progressive supranuclear palsy), or necropsy (all DLB cases and 24% of cases of progressive supranuclear palsy). Level of dementia severity was matched using the total score on the dementia rating scale adjusted for age and education.
Main outcome measures: Dementia rating scale subscores corrected for age.
Results: No significant differences between the dementia rating scale subscores in the PDD and DLB groups were found in the severely demented patients; in patients with mild to moderate dementia the conceptualisation subscore was higher in PDD than in DLB (p = 0.03). Compared with Alzheimer's disease, PDD and DLB had higher memory subscores (p < 0.001) but lower initiation and perseveration (p = 0.008 and p = 0.021) and construction subscores (p = 0.009 and p = 0.001). DLB patients had a lower conceptualisation subscore (p = 0.004). Compared with progressive supranuclear palsy, PDD and DLB patients had lower memory subscores (p < 0.001).
Conclusions: The cognitive profiles of patients with DLB and PDD were similar, but they differed from those of patients with Alzheimer's disease and progressive supranuclear palsy. The cognitive pattern in DLB and PDD probably reflects the superimposition of subcortical deficits upon deficits typically associated with Alzheimer's disease.
Dementia with Lewy bodies (DLB) and Parkinson's disease with dementia (PDD) are common syndromes characterised by parkinsonism and dementia. There are few comparisons of the clinical presentations of these syndromes, and differentiation between the disorders may occasionally be difficult in clinical practice. (12) Moreover, although there is some evidence suggesting pathological, (3) neurochemical, (4) and clinical (5) similarities, the nosological relation between the two syndromes has yet to be resolved.
The cognitive impairment in DLB is characterised by marked deficits in attention and in executive, visuospatial, and constructional abilities. (6) Memory is also impaired, although recall is relatively spared when compared with Alzheimer's disease. (7) A similar pattern of cognitive impairment is found in Parkinson's disease. (8) Nevertheless, two studies that directly compared cognition in PDD and DLB reported more executive dysfunction in the latter. (9, 10) However, the mean mini-mental state examination (MMSE) (11) score was only 12.5 in the DLB group compared with a nearly normal score of 24.1 in the Parkinson's disease group. (9)
To ensure that any between-group differences in subtest profiles are attributable to differences in the underlying nature of the two diseases rather than to differences in the global level of dementia, the two groups should be matched for overall severity of dementia. In the study by Downes et al, (10) clinically diagnosed PDD and DLB cases were carefully matched for dementia severity, but the study sample was small (only 10 patients in each group), the subjects were rather young (mean ages 64.9 and 66.4 years, respectively), and the level of cognitive impairment was mild (mean verbal IQ 97.2 and 94.1, respectively). Accordingly, the representativeness of these samples can be questioned.
Cortical and subcortical pathologies occur in both DLB and PDD, with potential implications for cognitive function, but the brain structures contributing to the cognitive impairment are still not clearly identified. Furthermore, differentiation of patients with DLB or PDD from those with dementia syndromes characterised by symptoms of mainly cortical pathology, such as Alzheimer's disease, or subcortical pathology, such as progressive supranuclear palsy, may be difficult. (1) Knowledge of the cognitive patterns in DLB and PDD in comparison with Alzheimer's disease and progressive supranuclear palsy could provide information about factors contributing to the cognitive dysfunction in these disorders, and could aid in the clinical diagnosis of dementia with parkinsonian syndromes and provide information on the nosological status of PDD and DLB.
With these aspects in mind, we used the dementia rating scale (12)--a brief measure of general cognitive status commonly used in both clinical practice and research--to study the performance of relatively large samples of patients with PDD, DLB, progressive supranuclear palsy, and Alzheimer's disease with similar levels of overall dementia. We hypothesised that the cognitive profiles of PDD and DLB cases are rather similar and are consistent with the presence of both cortical and subcortical dysfunction, in contrast with syndromes of cortical dementia (Alzheimer's disease) and subcortical dementia (progressive supranuclear palsy).
Parkinson's disease PDD patients were recruited from a community based cohort …