Psychiatric-onset prodromal dementia with lewy bodies: a comparative analysis of two cases.

Psychiatric-onset DLB refers to a prodromal presentation of DLB in which late-life psychiatric symptoms precede the characteristic cognitive and neurological features of DLB, often leading to an initial diagnosis of a primary psychiatric disorder. We report two women with psychiatric-onset DLB presentations who were followed longitudinally at a single institution. Case 1 presented with late-onset severe depression and anxiety, together with clinically suspected rapid eye movement sleep behavior disorder (RBD). Cognitive function was preserved, and dopamine transporter scintigraphy showed reduced striatal uptake, whereas myocardial metaiodobenzylguanidine scintigraphy and cerebral perfusion single-photon emission computed tomography showed no clinically meaningful abnormalities. A psychiatric-onset prodromal DLB presentation was suspected. Case 2 initially presented with depressive symptoms and mild cognitive impairment after cerebral aneurysm surgery and was first diagnosed with an organic mental disorder. Longitudinal follow-up revealed progressive cognitive decline, parkinsonism, autonomic dysfunction, and subsequent biomarker abnormalities approximately 9 years after the initial presentation, leading to a diagnosis of DLB. The total follow-up period to date is approximately 15 years. These cases highlight the heterogeneity of psychiatric-onset DLB and the importance of careful longitudinal reassessment in older adults with new-onset psychiatric symptoms.