Olfactory dysfunction predicts early transition to a Lewy body disease in idiopathic RBD

Neurology. 2015 Jan 21. pii: 10.1212/WNL.0000000000001265. [Epub ahead of print]

Mahlknecht P, Iranzo A, Högl B, Frauscher B, Müller C, Santamaría J, Tolosa E, Serradell M, Mitterling T, Gschliesser V, Goebel G, Brugger F, Scherfler C, Poewe W, Seppi K; For the SINBAR (Sleep Innsbruck Barcelona) Group; For the SINBAR Sleep Innsbruck Barcelona Group.

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.