[Reactive arthritis]

Reactive arthritis (ReA) is a disease caused by an extra-articular infection that manifests as a sterile joint inflammation. In contrast to bacterial septic arthritis no pathogens can be cultured from the joint in ReA but pathogen components, such as antigens or DNA are more frequently detectable in the joint, suggesting an intra-articular culture-negative persistent infection or at least an intra-articular interaction between the host and pathogen components. The primary extra-articular infection in classical ReA is of bacterial origin and usually affects either the urogenital, gastrointestinal or, less frequently, the respiratory tract. Chlamydia (C. trachomatis and less frequently C. pneumoniae) and enterobacteria are among the most common pathogens causing ReA. The prevalence of ReA is estimated at 40/100,000 and the incidence at 5/100,000. Typical clinical manifestations are mostly self-limiting peripheral arthritis (monoarticular or oligoarticular), dactylitis and, more rarely, axial involvement and in half of the cases, there is an association with HLA-B27. Due to these similarities, classical ReA is categorized as a form of spondyloarthritis (SpA). The diagnosis is made on the basis of a typical clinical picture, evidence of a previous or persistent infection and the exclusion of other causes of arthritis. Treatment includes physical measures, the use of anti-inflammatory agents such as nonsteroidal anti-inflammatory drugs (NSAID) or glucocorticoids, in the case of persistent arthritis, immunomodulating substances such as sulphasalazine, methotrexate and in individual cases biologics and Janus kinase inhibitors (JAKi) are used. In general, antibiotic treatment of ReA does not shorten the duration of the disease.