Nostril Differences in the Olfactory Performance in Health and Disease

In the past few decades, several olfactory tests have been developed to assess olfactory performance and detect disorders. Contrary to other sensory systems, both nostrils are usually tested together; we hypothesized that monorhinal testing may reveal side differences in sensitivity which may be useful for the diagnosis of olfactory dysfunction. Using the "Sniffin' Sticks" test, we assessed olfactory function of 458 participants (278 healthy controls, 180 hyposmic patients), one nostril after the other, with 3 different tasks. For each participant and each task, we compared the scores obtained with both nostrils, and defined the best and worst nostrils. Thus we were able to establish normative data and to define cut-off values. Our results suggest that scores obtained with the worst nostril are the most efficient in detecting an olfactory disorder. This supports the importance of monorhinal testing, as it can allow an earlier and more accurate diagnosis than birhinal testing. This may be especially useful in the context of early detection of neurodegenerative diseases.