Rapid Eye Movement Sleep Behavior Disorder with Clinical Dementia with Lewy Bodies Phenotype but Lacking Postmortem Central Nervous System Synuclein Pathology: Alternate Etiologies

RBD may arise independently of α-synuclein pathology. In the present case, RBD might be caused by dysregulation of the brainstem REM sleep-related structures due to age-related proteinopathies impairing the limbic system, and venlafaxine overactive monoaminergic transmission. In neuroprotective trials, CSF α-synuclein SAA may be useful to exclude IRBD patients without synuclein pathology. © 2026 International Parkinson and Movement Disorder Society.