Purpose of review: Thirty years ago, the concept of microscopic gut inflammation in spondyloarthritis (SpA) was established. Over the past decade, there has been tremendous progress in the earlier diagnosis of SpA. In addition, it has been suggested that, because of improved hygiene over the past years, exposure to microorganisms has changed, leading to a shift in diseases, for example, a decreased incidence of reactive arthritis. It is therefore necessary to re-establish the role of gut inflammation in SpA.
Recent findings: The prevalence of microscopic gut inflammation could be confirmed in c. 50% of patients with early axial and/or peripheral SpA. More importantly, a predictive model could be developed linking gut inflammation with clinical factors, that is, higher disease activity, extensive sacroiliac bone marrow edema, and progressive disease. In addition, there is increasing evidence indicating that the presence or absence of gut inflammation in SpA may influence therapeutic decision-making in the future. A clear demonstration of this is the different efficacy of IL-17 blockade in Crohn's disease versus SpA.
Summary: Microscopic gut inflammation is present in almost 50% of SpA patients and appears relevant for prognosis and therapeutic decision-making. SpA patients with the chronic type of gut inflammation seem to have a less favorable disease course. It is therefore conceivable that assessment of gut inflammation should be included in future models for risk stratification of SpA.