Reactive arthritis (ReA), and enteropathic arthritis secondary to inflammatory bowel disease, are forms of spondyloarthritis, all of which share an association with HLA B27 and can involve both axial and peripheral joints. Genetic studies strongly implicate the cytokines IL-17 and IL-23 in their pathogenesis, and evidence for autoimmunity is lacking. ReA is triggered by particular bacteria, mainly affecting the gut and genitourinary tract, though infections are sometimes asymptomatic. Classically an acute oligo- or monoarthritis with enthesitis occurs, often with inflammatory back pain, though mild polyarthritis can also occur. Septic and crystal-induced arthritis are the principal differential diagnoses. Extra-articular features may aid diagnosis, which otherwise requires laboratory evidence of preceding infection. Bacterial components traffic to the joint (which is nevertheless sterile), and elicit local pro-inflammatory immune responses. Most ReA is self-limiting, but persistent cases may require disease-modifying anti-rheumatic drugs or even biologics.
Autoinflammatory Mechanisms in Crystal-Induced Arthritis
