26th February 2025

Adult-onset Still’s disease (AOSD)

AOSD is the term for systemic juvenile idiopathic arthritis when seen in a patient over 16 years old.

It typically presents with daily fevers, a salmon-coloured maculopapular rash and arthritis. The rash is usually non-pruritic and flares with episodes of fever. Joint involvement can initially be in an oligoarticular pattern but progresses to a more severe polyarthritis. Sore throat, lymphadenopathy and splenomegaly may also be found.

There is no definitive diagnostic test. ESR and CRP are markedly raised, and there is a neutrophilic leucocytosis. Elevated ferritin is very common and likely represents an acute phase response. Typically, antibodies are negative.

Mild-to-moderate disease is treated with NSAIDs once other causes are excluded. If patients do not respond to NSAIDs, either glucocorticoids or biologic therapy are initiated. Biologic therapy is usually with IL-1 inhibitors such as anakinra or canakinumab.