Discerning dementia with Lewy bodies (DLB) from Alzheimer's disease (AD) is one of the most common and challenging differential diagnoses at the memory clinic. Although the neuropsychiatric manifestations have been widely reported as one of the main key points in the differential diagnosis between these two diseases, to date no neuropsychiatric questionnaire has been specifically devised for this purpose.

We administered the Neuropsychiatric Inventory (NPI) and the Columbia University Scale for Psychopathology in Alzheimer's Disease (CUSPAD) to a memory clinic sample of 80 patients with probable DLB and 85 age- and severity-matched patients with probable AD. Diagnosis of probable DLB was supported with a positive dopamine transporter SPECT scan. We examined the usefulness of these two neuropsychiatric tools designed for AD in the differential diagnosis between DLB and AD. We also investigated the correlations between psychotic symptoms and measures of cognitive and functional decline.

Auditory hallucinations were very specific of DLB and were usually preceded by visual hallucinations. Misinterpretation of real visual stimuli (illusions) was more frequent in DLB. Delusions were both quantitatively and qualitatively different between DLB and AD: delusional misidentifications were significantly more characteristic of DLB, while paranoid delusions did not show specificity for DLB.

Neuropsychiatric tools are useful to discriminate DLB from AD. Hallucinations and delusions are not only more frequent in DLB than in AD but also have distinct qualitative characteristics and patterns of progression that can help clinicians to make a more accurate differential diagnosis.