Therapeutic alteration of the microbiota in rheumatic diseases: Hype or potential?

Multiple studies have demonstrated abnormalities in the contents of the fecal microbiota in patients with a variety of forms of arthritis. This has prompted interest in microbial-altering therapy as a therapeutic tool. While antibiotics as a long-term therapeutic tool have largely fallen out of favor, there have been multiple studies evaluating probiotics in rheumatoid arthritis, spondyloarthritis, or systemic sclerosis; a small number of studies have tested fecal microbial transplantation (FMT) in rheumatic diseases. Although probiotics were well tolerated, few studies detected meaningful clinical benefit regardless of indication. Likewise, one of the two randomized studies evaluating FMT showed minimal clinical benefit, while the other demonstrated worsening compared to sham treatment. In this review article, I summarize the literature on probiotics and FMT in rheumatic diseases, discuss potential reasons for the absence of demonstrable benefit, and suggest avenues of future direction of research.