Alterations of the brain network in idiopathic rapid eye movement sleep behavior disorder: structural connectivity analysis Abstract Purpose To evaluate and compare structural connectivity using graph theoretical analysis in patients with idiopathic rapid eye movement sleep behavior disorder (iRBD) and healthy subjects. Methods Ten consecutive patients with iRBD were recruited from a single tertiary hospital. All patients had normal brain magnetic resonance imaging results on visual inspection. They did not have any other neurological disorder. Control subjects were also enrolled. All subjects underwent three-dimensional volumetric T1-weighted imaging. Absolute structural volumes were calculated using FreeSurfer image analysis software. Structural volume and connectivity analyses were performed with Brain Analysis using Graph Theory. Results Compared to healthy controls, patients with iRBD showed significant alterations in cortical and subcortical volumes, showing increased volumes of frontal cortex, thalamus, and caudate nucleus. In addition, patients with iRBD exhibited significantly different structural connectivity compared to healthy controls. In measures of global network, average degree, global efficiency, and local efficiency were decreased whereas characteristic path length was increased in iRBD patients. In measures of local network, there was significant hub reorganization in patients with iRBD. Betweenness centrality of caudate nucleus and frontal cortex was increased in patients with iRBD. Conclusions This is the first study to report that structural volume and connectivity in patients with iRBD are significantly different from those in healthy controls. iRBD patients exhibited disrupted topological disorganization of the global brain network and hub reorganization. These alterations are implicated in the pathogenesis of iRBD. They might be potential biomarkers of iRBD.