Neuropsychological differentiation between Alzheimer's disease and dementia with Lewy bodies in a memory clinic.

OBJECTIVE

The aim of this study was to identify a useful neuropsychological instrument for making a differential clinical diagnosis between Alzheimer's disease (AD) and dementia with Lewy bodies (DLB).

METHODS

We examined 402 AD and 38 DLB patients with neuropsychological tests that covered general cognition, frontal lobe cognitive function, non-verbal abstract reasoning, working memory and attention, and verbal memory. Discriminant analysis using a stepwise method was performed to identify the measures best able to discriminate between AD and DLB.

RESULTS

The AD patients performed significantly worse than the DLB patients on orientation to time, delayed recall subtests on the Mini-Mental State Examination, and logical memory subtests 1 and 2 of the Revised Wechsler Memory Scale. The DLB patients performed significantly worse than the AD patients on the attention, repetition, and pentagon copying subtests of the Mini-Mental State Examination, the constructional praxis subtests of the Alzheimer's Disease Assessment Scale-cognitive component-Japanese version, the Frontal Assessment Battery total score, Raven's Coloured Progressive Matrices (RCPM) sets A, AB, and B, and backward digit span. Discriminant analyses between AD and DLB established the key variables as Logical Memory 1, Logical Memory 2, backward digit span, RCPM, and delayed recall on the Mini-Mental State Examination. We inferred the AD-DLB discriminant index from the following discriminant analyses: AD-DLB discriminant index = (Backward digit span score + RCPM set B score) - (Logical Memory 1 score + Logical Memory 2 score), which offered a highly favourable value for diagnostic utility.

CONCLUSIONS

The AD-DLB discriminant index, consisting of backward digit span, RCPM set B, and logical memory 1 and 2, is useful to differentiate between AD and DLB.