Relevance of substantia nigra hyperechogenicity and reduced odor identification in idiopathic REM sleep behavior disorder

Abstract: Background: Substantia nigra (SN) hyperechogenicity determined by transcranial sonography (TCS) and olfactory dysfunction are common findings in Parkinson disease (PD), which may reveal a prodromal synucleinopathy in idiopathic REM sleep behavior disorder (iRBD). Methods: TCS and the Odor Stick Identification Test for Japanese (OSIT-J) were performed in 34 consecutive patients with iRBD (67.9±6.1years), 17 consecutive patients with PD (66.4±6.7years), and 21 control group subjects (64.4±5.8years). Results: There was a significantly increased area of echogenicity in the SN in the iRBD group (0.20±0.13cm2) and PD group (0.22±0.11cm2) compared with the control group (0.06±0.06cm2). We found pathological SN hyperechogenicity (⩾0.20cm2) in 41.2% of the iRBD group, 52.6% of the PD group, and 9.5% of the control group. Further, there were abnormal findings of both pathological SN hyperechogenicity (⩾0.20cm2) and functional anosmia or hyposmia in 4 (11.8%) or 9 (26.5%) of the iRBD group subjects, respectively, and 7 (57.9%) or 2 (11.8%) of the PD group subjects, respectively. Conclusion: Pathological SN hyperechogenic abnormality and functional anosmia in iRBD may be a disease state in the transition to a neurodegenerative disease. [Copyright &y& Elsevier]