Exploring Nasal Structural‐Microbial Interactions in Multiple Sclerosis‐Associated Olfactory Impairment

Olfactory dysfunction is frequently observed in patients with multiple sclerosis (MS); however, its underlying mechanisms remain poorly understood. To date, no studies have directly examined the nasal mucosal microbiota in MS. This study aimed to explore potential relationships among olfactory function, nasal microbiota composition, and superior turbinate volume in MS. This single-center observational study included 42 patients with MS and 37 healthy controls (HC) in China. Olfactory function was evaluated using the University of Pennsylvania Smell Identification Test (UPSIT). Deep nasal microbiota profiles and MRI-based measurements of superior turbinate volume were analyzed. A reduced relative abundance of Prevotella buccalis (P. buccalis) was observed in MS with lower UPSIT scores (p = 0.030). In HC, a positive correlation was found between UPSIT scores and the superior turbinate volume (Rp = 0.329, p = 0.041), whereas no such correlation was observed in MS (Rs = -0.022, p = 0.625), suggesting a dissociation between olfactory performance and turbinate morphology in MS. Additionally, in MS, superior turbinate volume showed negative correlations with several genera, including Cupriavidus, Methylobacterium-Methylorubrum, Ideonella, and Acinetobacter (all p < 0.05), indicating potential associations between mucosal structure and microbial composition. These preliminary findings suggest that alterations in nasal microbiota may be linked to olfactory impairment and mucosal structural changes in MS. While P. buccalis emerged as a potential microbial correlate of olfactory dysfunction, its role remains unclear and may reflect secondary ecological shifts. Further mechanistic studies and larger cohorts are needed to determine causality and assess the diagnostic or therapeutic value of nasal microbiome features in MS.