Odor identification test as an indicator of idiopathic REM sleep behavior disorder.

Reduction of olfactory function in idiopathic rapid-eye-movement (REM) sleep behavior disorder (iRBD) is of the same magnitude as that found in patients with Parkinson's disease (PD) and dementia with Lewy bodies (DLB). We assessed olfactory function using the Odor Stick Identification Test for Japanese (OSIT-J) in 48 Japanese patients with iRBD, 21 with PD, and 34 with obstructive sleep apnea syndrome (OSAS). Possible score of the OSIT-J ranges from 0 to 12. OSIT-J scores were 4.9 +/- 2.8 in patients with iRBD, 4.8 +/- 2.8 in patients with PD, and 9.9 +/- 1.4 in OSAS patients. An OSIT-J score of 8.5 was associated with a sensitivity of 88.2 and 85.3%, respectively, and specificity of 83.3 and 85.7%, respectively, in differentiating iRBD or PD patients from OSAS patients. Odor identification is impaired in Japanese patients with iRBD and PD. The results suggest that OSIT-J, which is a short and simple nonlexical olfactory identification test, can be useful as a clinical indicator for iRBD with Lewy body formation and is appropriate in the Japanese elderly population.