AOSD

Adult-onset Still's disease (AOSD) is a rare autoinflammatory disorder characterized by systemic inflammation with fevers, arthritis, and a salmon-pink skin rash, along with elevated inflammatory markers. It primarily affects adults, often presenting in the second to fourth decades of life, though onset can occur at any age. The exact cause is unknown, but genetic susceptibility and environmental triggers are thought to contribute, and dysregulated innate immune responses with proinflammatory cytokines play a central role.

Clinical presentation commonly includes quotidian fever spikes (often above 39°C), arthritis that can be symmetrical and involve large joints, and an evanescent rash that rises with fever. Additional symptoms may include sore throat, lymphadenopathy, hepatosplenomegaly, abdominal pain, weight loss, and fatigue. Laboratory findings typically show marked leukocytosis with neutrophilia, elevated CRP and ESR, and markedly elevated ferritin levels, which may be extremely high. Hyperferritinemia with a low glycosylated ferritin fraction is frequently observed. Liver enzymes can be abnormal, and other autoimmune markers are usually negative.

Diagnosis is clinical and by exclusion of infections, malignancies, and other rheumatic diseases. There is no single diagnostic test. Established criteria, such as the Yamaguchi or Fautrel criteria, guide diagnosis, emphasizing a combination of major and minor features and the exclusion of other conditions. MAS (macrophage activation syndrome) is a potential life-threatening complication.

Treatment ranges from nonsteroidal anti-inflammatory drugs for mild disease to systemic glucocorticoids for more active disease, often with steroid-sparing DMARDs such as methotrexate. Biologic therapies targeting IL-1 (anakinra, canakinumab) or IL-6 (tocilizumab) are effective in many patients. Prognosis is variable; some patients achieve remission, while others have relapsing disease or develop chronic arthritis, with rare but serious complications such as MAS or secondary amyloidosis.