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

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 +/- 6.1 years), 17 consecutive patients with PD (66.4 +/- 6.7 years), and 21 control group subjects (64.4 +/- 5.8 years). Results: There was a significantly increased area of echogenicity in the SN in the iRBD group (0.20 +/- 0.13 cm(2)) and PD group (0.22 +/- 0.11 cm(2)) compared with the control group (0.06 +/- 0.06 cm(2)). We found pathological SN hyperechogenicity (>= 0.20 cm(2)) 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 (>= 0.20 cm(2)) 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. (C) 2010 Elsevier B.V. All rights reserved.