Differential Progression of Neuroinflammation in Patients with Isolated Rapid‐Eye‐Movement Sleep Behavior Disorder

Background Neuroinflammation, measured using [ 11 C]( R )‐PK11195 positron emission tomography (PET), has been reported in isolated rapid‐eye‐movement sleep behavior disorder (iRBD), but its temporal progression is unknown. Objective The aim was to assess longitudinal progression of neuroinflammation in iRBD patients and its relationship with phenoconversion into Parkinson's disease (PD) or dementia with Lewy bodies (DLB). Methods Sixteen iRBD patients received longitudinal [ 11 C] (R) ‐PK11195 PET scans over 3 years and were followed up clinically for 8 years to record phenoconversion into PD and DLB. Results We found significant progression of neuroinflammation in the putamen among other regions, with a trend to cortical increase over 3 years. During the clinical follow‐up, 7 patients converted, and subgroup analyses suggested that the converters differed in progression patterns, with PD converters exhibiting increases and DLB exhibiting decreases in inflammation. Conclusion This exploratory study suggests that progression of neuroinflammation in iRBD patients depends on their clinical trajectories, and this could be impactful in immune‐modifying treatments.