Mild behavioral impairment and its relation to amyloid load in isolated REM sleep behavior disorder

In isolated REM sleep behavior disorder (iRBD), the evidence of cognitive impairment and co-existing amyloid pathology suggests that mild behavioral impairment (MBI) may be associated with disease progression. In this study, we investigated MBI and its association with cognitive function, brain amyloid load and glucose metabolism in iRBD patients to evaluate the utility of MBI as a predictive marker of disease progression.

Patients with iRBD underwent a neuropsychological evaluation, ¹⁸F-florbetaben (FBB) PET, and ¹⁸F-fluorodeoxyglucose (FDG) PET. MBI was evaluated using the MBI-checklist (MBI-C). Comparisons between MBI-positive and MBI-negative groups and correlations with MBI-C total scores were examined on neuropsychological performances and PET regional standardized uptake value ratios (SUVRs). Additionally, associations between regional amyloid burden and glucose metabolism and mediating role of MBI status on these associations were evaluated in all iRBD patients.

Of 36 iRBD patients, about one-third were classified as MBI-positive. Although we did not find the differences between the MBI groups and correlations with MBI-C total scores in neuropsychological performances and brain glucose metabolism, the MBI-positive group revealed higher FBB SUVRs in the anterior cingulate cortex, prefrontal cortex, caudate nucleus, and putamen than the MBI-negative group. The FBB SUVR of caudate nucleus was negatively correlated with glucose metabolism in the precuneus, which was not directly mediated by the MBI.

Characteristic amyloid accumulation in prefrontal and subcortical structures in MBI-positive iRBD patients suggests that MBI may be associated with early amyloid pathology that can be an integral role in disease progression.