The periodontal pathogen Fusobacterium nucleatum is associated with disease severity in multiple sclerosis.

Increasing evidence suggests that periodontitis may contribute to central nervous system disorders through chronic inflammation, but its role in multiple sclerosis (MS) remains unclear. This exploratory, cross-sectional study investigated the associations between the relative abundance of periodontal pathogens in the oral cavity and the clinical characteristics of MS. We enrolled 98 patients with MS, neuromyelitis optica spectrum disorder, or myelin oligodendrocyte glycoprotein antibody-associated disease. Tongue coating samples were analyzed using quantitative polymerase chain reaction targeting four periodontal species. High relative abundance was defined as an abundance exceeding the third quartile in proportion to the total abundance of bacteria. Associations between clinical and MRI features were assessed. Among the 56 patients with MS, only a high relative abundance of Fusobacterium nucleatum was associated with disease severity, as measured by the Expanded Disability Status Scale (EDSS) (p = 0.009). No associations were observed for the other three pathogens or in the non-MS groups. In a multivariate analysis, a high relative abundance of Fusobacterium nucleatum remained independently associated with the EDSS score. These findings suggest a potential association between the relative abundance of Fusobacterium nucleatum in the oral cavity and disease severity in MS.