Adult-onset Still’s disease (AOSD) is a rare inflammatory disorder characterized by high fevers, joint pain, and a distinctive salmon-pink rash. It typically affects adults under 45 but can occur at any age. Symptoms often include:
Fever: Daily spikes, often exceeding 39°C (102°F), lasting at least a week.

Arthritis/Arthralgia: Joint pain or inflammation, commonly in wrists, knees, or ankles.

Rash: A fleeting, salmon-colored rash, usually on the trunk or limbs, often appearing during fever spikes.

Other symptoms: Sore throat, swollen lymph nodes, muscle pain, or organ involvement (e.g., liver, spleen).

Causes and Risk Factors
The exact cause is unknown, but AOSD is considered an autoinflammatory condition, possibly triggered by infections, genetics, or immune dysregulation. No clear risk factors are established, though it slightly favors women.
Diagnosis
Diagnosis is challenging due to nonspecific symptoms and lack of a definitive test. It’s often based on:
Clinical criteria: Yamaguchi or Fautrel criteria, requiring symptoms like fever, arthritis, and rash, while excluding other conditions (e.g., infections, cancers, or other autoimmune diseases).

Lab tests: Elevated inflammatory markers (CRP, ESR), high ferritin levels, and leukocytosis. Negative rheumatoid factor and ANA tests help rule out similar conditions.

Imaging: To assess joint damage or organ involvement.