Adult-onset Still's disease (AOSD) is a form of Still's disease, a rare systemic autoinflammatory disease characterized by the classic triad of persistent high spiking fevers, joint pain, and a distinctive salmon-colored bumpy rash. The disease is considered a diagnosis of exclusion.Specialty: Rheumatology. Adult Still disease (ASD) is a rare illness that causes high fevers, rash, and joint pain. It may lead to long-term (chronic) arthritis. Adult Still disease is a severe version of juvenile idiopathic arthritis (JIA), which occurs in children. Adults can have the same condition, although it is much less common.