BackgroundThe close relationship between joints and gut inflammation has long been known and several data suggest that dysbiosis could link spondyloarthritis (SpA) to inflammatory bowel diseases (IBD). The introduction of biological drugs, in particular tumour necrosis factor inhibitors (TNFi), revolutionised the management of both these diseases. While the impact of conventional drugs on gut microbiota is well known, poor data are available about TNFi.AimTo investigate the impact of TNFi on gut microbiota.MethodsWe evaluated 20 patients affected by enteropathic arthritis, naïve for biological drugs, treated with TNFi at baseline and after 6 months of therapy. All patients followed a Mediterranean diet. Patients performed self-sampling of a faecal sample at baseline and after 6 months of therapy. NGS-based ITS and 16S rRNA gene sequencing was performed, followed by the taxonomic bioinformatics analysis.ResultsAfter 6 months of therapy, we detected a remarkable increase in Lachnospiraceae family (Δ +10.3, p=0.04) and Coprococcus genus (Δ +2.8, p=0.003). We also noted a decreasing trend in Proteobacteria (Δ −8.0, p=0.095) and Gammaproteobacteria (Δ −9, p=0.093) and an increasing trend in Clostridia (Δ +8.2, p=0.083). We did not find differences between TNFi responders (SpA improvement or IBD remission achieved) and non-responders in terms of alpha and beta diversity.ConclusionsOur findings are consistent with the hypothesis that TNFi therapy tends to restore the intestinal eubiosis.