Coexisting Amyloid Positivity and Probable Dementia With Lewy Bodies in a Patient With Rapid Eye Movement Sleep Behavior Disorder.

BACKGROUND Rapid eye movement (REM) sleep behavior disorder (RBD) is a REM-related parasomnia in which the normal muscle atonia of REM sleep is lost, leading to complex motor behaviors or dream enactments. RBD is increasingly recognized as a prodromal manifestation of neurodegenerative a-synucleinopathy. It is well established in longitudinal studies that isolated RBD is among the strongest predictors of a-synucleinopathies, with more than 80-90% of patients eventually converting to Parkinson disease, dementia with Lewy bodies (DLB), or multiple system atrophy. CASE REPORT We report a 69-year-old woman with a previous history of RBD who was admitted for progressive cognitive and behavioral deterioration after starting antiseizure and antipsychotic medications. On admission, she exhibited bradykinesia and rigidity and dopamine transporter positron emission tomography (PET) imaging demonstrated reduced uptake in the putamina. During hospitalization, dream-enacting behaviors were observed, leading to the decision to conduct polysomnography, which confirmed loss of muscle atonia during REM sleep. Taken together, these findings supported a diagnosis of DLB and RBD. In addition, brain magnetic resonance imaging with susceptibility-weighted sequences revealed multiple cortical microbleeds consistent with cerebral amyloid angiopathy, prompting amyloid PET imaging, which showed diffuse cortical amyloid deposition and indicated concurrent amyloid pathology. CONCLUSIONS This case highlights that RBD and characteristic neuroimaging findings are consistent with DLB as the primary disease, with coexisting amyloid pathology. Additionally, the potential influence of clinical confounders such as cerebral amyloid angiopathy, seizure, and medication effects must be taken into account.