The role of the gastrointestinal microbiome on rheumatoid arthritis, psoriatic arthritis, ankylosing spondylitis and reactive arthritis: A systematic review

Background: There is an increasing body of literature observing a state of dysbiosis in the gut microbiome in different autoimmune conditions including inflammatory arthritis. It is unknown whether the microbiome can be a biomarker for prognostication purposes or for stratification of treatment strategies. This review aims to evaluate the existing evidence on the association between the microbiome and inflammatory arthritis, including rheumatoid arthritis (RA), psoriatic arthritis (PsA) and ankylosing spondylitis (AS) and reactive arthritis (ReA) population groups. Methods: This systematic review was performed based on methods from the Cochrane guidelines and reported based on PRISMA criteria. Studies exploring the microbiome of patients with RA, AS, PsA or ReA compared with controls via 16s rRNA or shotgun sequencing were evaluated. The outcomes of interest include alpha and beta diversity, abundance or depletion of organisms and functional analysis. Literature up to August 2024 was retrieved searching the databases PubMed, Medline, ScienceDirect, Scopus, Web of Science, Cochrane, EMBASE and CINAHL. All references were systematically evaluated by two reviewers. Quality of the studies were evaluated by the Newcastle-Ottawa Scale. Findings: The review yielded 25,794 search results, of which 53 studies were included for the RA group, 34 studies for the AS group, 6 studies for the PsA group and 2 studies for the ReA group. Reduced diversity has been observed in disease groups and in patients with higher disease activity. Interpretation: There are limited longitudinal studies on the role of the microbiome in inflammatory arthritis, in particular PsA. Existing cross-sectional studies suggest altered microbiome in disease states compared with controls. Further studies are required to understand the utility of the microbiome as a biomarker to better understand prognosis and tailor treatments.