Fecal Microbiota Transplantation in Axial Spondyloarthritis

Inclusion Criteria: * Axial Spondyloarthritis according to the ASAS classification criteria * Active disease defined as ASDAS ≥2.1 with elevated CRP ≥3 OR active inflammation on MRI within the last 3 months * Onset of axial SpA within last 10 years * Unsatisfactory relief of NSAIDs * On stable immunomodulatory treatment (TNFi, IL17i or JAKi) the last 3 months OR without immunomodulatory treatment last 3 months Exclusion Criteria: * Planned dose adjustment or change in immunomodulatory treatment the next 90 days * Disease or disorder with life expectancy of ≤5 years * Severe immune deficiency (acquired, congenital og du to medication) * Previous treatment with FMT * Regular use of opioids with the exception of codeine and tramadol * Any specific diagnosis that could explain or contribute to the patients back pain (e.g. tumor, fracture, infection or degenerative disease) * Inflammatory spinal disease other than axSpA * Severe psychiatric disorder, alcohol- or drug abuse * Active inflammatory bowel disease * Microscopic colitis, diverticulitis or ileus * Active psoriasis * Fibromyalgia * Abdominal surgery excluding appendectomy, cholecystectomy, hysterectomy, caesarian section, sapling-ooforectomy and hernia surgery * Malignant disease excluding basalioma and melanoma stage 1 * Conditions with expected necessary treatment with antibiotics during the study period, e.g. periodontitis end ischemic digital ulcers * Treatment with antibiotics 12 weeks prior to study entry * Pregnancy, lactation or planned pregnancy within the next 3 months * Contraindications for rectal catheter insertion * Planned rehabilitation program the next 90 days * Limited ability to comply with protocol requirements, including biobank participation