Mild behavioral impairment in idiopathic REM sleep behavior disorder and Lewy body disease continuum.

To investigate the clinical impact of mild behavioral impairment (MBI) in a predefined cohort with Lewy body disease (LBD) continuum. Eighty-four patients in the LBD continuum participated in this study, including 35 patients with video-polysomnography-confirmed idiopathic REM sleep behavior disorder (iRBD) and 49 clinically established LBD. Evaluations included the Movement Disorder Society-Unified Parkinson's Disease Rating Scale (MDS-UPDRS), neuropsychological tests, and MBI Checklist (MBI-C). We examined the clinical associates of MBI-C and its diagnostic values in predicting disease severity and cognitive impairment across the LBD continuum. Participants were classified into 19 cognitively normal (CN), 45 mild cognitive impairment (MCI), and 20 dementia groups. Median MBI-C total scores were 1.0, 8.0, and 18.5 for CN, MCI, and dementia groups, respectively, with a significant increasing trend (p < 0.001). The MBI-C total score demonstrated significant correlations with the MDS-UPDRS part 1 (r = 0.504, p < 0.001) and total scores (r = 0.508, p < 0.001). Furthermore, significant correlations were observed between MBI-C and cognitive performances in frontal/executive (DSC: r = -0.314, p = 0.006; TMT-B: r = -0.338, p = 0.003) and attentional (TMT-A: r = -0.343, p = 0.002) domains. A cutoff 5.0 effectively differentiated the MCI from CN groups (area under the curve (AUC = 0.74). Furthermore, the MBI-C effectively discriminated the iRBD patients with high phenoconversion risk against those with low-risk (cut-off 4.0, AUC = 0.72). The MBI-C may be a useful screening questionnaire reflecting clinical severity across the LBD continuum. Longitudinal studies are needed to determine its value in monitoring disease progression in prodromal LBD.