Title of Case:

A rare case of systemic junevile idiopathic arthritis (sJIA) in a 10-month-old infant initially diagnosed as MIS-C

Background:

sJIA is a multisystem inflammatory disease accounting for 10–20% of JIA cases that rarely affects infants. Clinical manifestations vary among young children. Immune system reaction is mainly activated by interleukin-1 and interleukin-6. Newly emerging biologic agents targeting those markers showed promising results.

Case Presentation Summary:

A previously healthy 10-month-old female infant was admitted with a two day history of high fever, rash and diarrhea. Clinical examination was otherwise unremarkable. Inflammatory markers were highly elevated. Therefore, wide-spectrum antibiotics were administered. Due to the continuation of fever, two systems involvement (skin, gut) and increased inflammatory markers, the clinical suspicion of MIS-C emerged. Treatment with IVIG, methylprednisolone and aspirin was initiated. Echocardiogram and abdominal ultrasound were normal. Testing for infectious causes including Sars-Cov-2 serology was negative. NGS was performed in order to screen for antoinflammatory diseases presenting in the infantile age with prolonged fever and systemic inflammation. No mutations were detected.

Despite the aforementioned treatment, clinical manifestations including high fever and widespread evanescent salmon-pink maculopapular rash did not subside. Inflammatory markers remained high. Diagnosis of MIS-C was revisited and the clinical suspicion of sJIA emerged. Treatment with anti-IL-6 agent was initiated. Subsequently, fever subsided and inflammatory markers improved. The infant was discharged in excellent condition, with a milder rash appearing during evening hours. Two months after discontinuation of corticosteroids, she suffered a relapse and was treated successfully with an anti-IL-1β blocker (canakinumab). She remains in remission eversince.

Learning Points/Discussion:

Clinical presentation of sJIA can be non-specific among infants and diagnosis may delay, especially during Covid-19 pandemic. Biologic agents have gained a major role in sJIA therapy with encouraging results.