Background: The cognitive profile of mild dementia with Lewy bodies (DLB) versus mild Alzheimer’s disease (AD) has not been extensively studied, and the relation of cognitive deficits to the core diagnostic criteria for DLB (fluctuations, visual hallucinations, and parkinsonism) remains poorly understood.

Objective: To compare the cognitive profile in patients with mild DLB to patients with mild AD and investigate the relation between cognitive deficits distinguishing DLB from AD and the core diagnostic features in DLB. Methods: Patients with mild dementia were recruited from the southwestern part of Norway and patients diagnosed with probable AD (n= 113) or probable DLB (n= 77) were included. The DLB core diagnostic symptoms were assessed using standardized clinical measures, and standardized neurocognitive tests assessing attention, language, memory, and visuospatial functions were administered. Univariate and multivariate comparisons of cognitive tests were performed, and tests distinguishing between AD and DLB were subjected to correlational analyses with the core diagnostic symptoms. Results: DLB patients performed worse than AD patients on test of visuoconstruction, but not visual perception and on all tests involving attention and executive functions, except verbal fluency. The multivariate model distinguished between DLB and AD with a sensitivity of 74% and a specificity of 82%. Tests where DLB performed worse than AD were highly correlated with degree of parkinsonism, but not with cognitive fluctuations or visual hallucinations. Conclusions: The cognitive profile in mild DLB can be useful in distinguishing AD from DLB. The strong relation between relative deficits in DLB and parkinsonism warrants further studies.