Olfactory dysfunction in idiopathic REM sleep behavior disorder

Background: Olfactory dysfunction is frequently observed in patients with idiopathic REM sleep behavior disorder (iRBD) such as Parkinson's disease or dementia with Lewy bodies. Methods: Olfactory function tests using Sniffin' Sticks and Odor Stick Identification Test for Japanese (OSIT-J) were performed in 73 consecutive middle-aged (range, 50-69 years) patients with iRBD, 33 consecutive older-aged (71-82 years) patients with iRBD, and 28 control subjects (55-70 years). Results: Odor identification was more frequently impaired than odor threshold or discrimination among the iRBD group and allowed better discrimination between the middle-aged iRBD group and age-adjusted control subjects. The area under the curve for threshold, discrimination, identification, TDI score and OSIT-J score determined from receiver operating characteristic curves were 0.831 (0.753-0.909), 0.761 (0.666-0.855), 0.938 (0.894-0.982), 0.939 (0.897-0.981), and 0.965 (0.931-0.999), respectively. Discrimination and identification scores were significantly lower in the older-aged iRBD group than in the middle-aged iRBD group. A significant correlation was observed between the identification score on Sniffin' Sticks and OSIT-J score (r = 0.5910, P < 0.0001, n = 106, Spearman's rank). Conclusion: Anosmia/hyposmia may be a feature of iRBD. Olfactory dysfunction in iRBD is a consistent, widespread central nervous abnormality of different olfactory modalities with different cognitive complexity. (C) 2010 Elsevier B.V. All rights reserved.