Olfactory dysfunction in patients with multiple sclerosis

Association of changes in olfactory-related structures with olfactory function in patients with multiple sclerosis (MS) is not well understood. We used a T&T olfactometer test kit to evaluate olfactory function in 26 patients with MS and 26 age- and sex-matched healthy controls (HC). Then, Brain MRI were performed and olfactory-related structures were analyzed in these subjects. Olfactory detection and recognition threshold were significantly higher in the MS group, interestingly olfactory recognition threshold positively correlated with expanded disability status scale scores in these patients. Olfactory bulb (OB) volume reduced in patients with olfactory dysfunction (ODF). At the same time, reductions in gray matter (GM) volume were observed in the parahippocampal gyrus (PCG), amygdala, piriform cortex, and inferior frontal gyrus in patients with MS compared to HC. Atrophy of the PCG was more obvious in patients with ODF than patients without ODF and the PCG volume correlated with the olfactory recognition threshold, while no difference was found in fractional anisotropy values of tract-based spatial statistics analysis in the two groups. Olfactory function in patients with MS tends to become gradually more impaired with disability aggravation. Decreases in the volume of the OB and olfactory-related GM might provide valuable information about disease status in patients with MS with olfactory impairment.