Neurology 2015 Feb 21;84(7):654-8. Epub 2015 Jan 21.
From the Department of Neurology (P.M., B.H., B.F., C.M., T.M., V.G., F.B., C.S., W.P., K.S.), Medical University Innsbruck; Department of Medical Statistics, Informatics and Health Economics (G.G.), Medical University Innsbruck, Austria; Neurology Service (A.I., J.S., E.T., M.S.), Hospital Clinic, Barcelona; Centro de Investigación Biomédica en Red Enfermedades Neurodegenerativas (CIBERNED) (A.I., J.S., E.T., M.S.); and IDIBAPS (A.I., J.S., E.T., M.S.), Barcelona, Spain.
Objective: The aim of the present study was to determine the predictive value of olfactory dysfunction for the early development of a synuclein-mediated neurodegenerative disease in subjects with idiopathic REM sleep behavior disorder (iRBD) over an observational period of 5 years.
Methods: Thirty-four patients with polysomnography-confirmed iRBD underwent olfactory testing using the entire Sniffin' Sticks test assessing odor identification, odor discrimination, and olfactory threshold. Patients with iRBD were prospectively followed up over a period of 4.9 ± 0.3 years (mean ± SD). The diagnosis of neurodegenerative diseases was based on current clinical diagnostic criteria.
Results: After 2.4 ± 1.7 years (mean ± SD), 9 patients (26.5%) with iRBD developed a Lewy body disease (6 Parkinson disease and 3 dementia with Lewy bodies). The entire Sniffin' Sticks test and the identification subtest had the same overall diagnostic accuracy of 82.4% (95% confidence interval: 66.1%-92.0%) in predicting conversion. The relative risk for a Lewy body disease in the lowest tertile of olfactory function was 7.3 (95% confidence interval: 1.8-29.6) compared with the top 2 tertiles.
Conclusions: Assessment of olfactory function, particularly odor identification, may help to predict the development of a Lewy body disease in patients with iRBD over a relatively short time period and thus to identify patients suitable for future disease modification trials.