Systemic-onset juvenile idiopathic arthritis

Systemic-onset juvenile idiopathic arthritis, also called Still disease, is a childhood form of arthritis marked by joint inflammation combined with distinctive systemic features, typically affecting children between one and five years old and making up 10 to 20 percent of juvenile idiopathic arthritis cases. It presents with a characteristic fever pattern, spiking above 39 degrees Celsius once or twice daily before rapidly returning to normal, and more than 80 percent of children develop a salmon-colored, migratory, non-itching rash. Its underlying cause remains unknown; infectious organisms have been suspected but microbiologic and virologic analyses have failed to identify a single causative agent, and the disease is now classified as autoinflammatory rather than autoimmune because no specific antigen-antibody relationship has been identified, with the innate immune system producing excess interleukin-1 and interleukin-6. The condition affects children of all genders and ethnicities roughly equally, though prevalence runs slightly higher in Japan and India than in North America.