Introduction: Kawasaki disease (KD) is an acute vasculitis of childhood with characteristic mucocutaneous and systemic features. Several inflammatory conditions may closely mimic KD, posing diagnostic challenges and therapeutic implications. Although systemic-onset juvenile idiopathic arthritis (soJIA) or Still’s disease, is not frequently presenting as a KD mimicker or overlap syndrome, clinical overlapping features and similar immunological pathways might be involved, particularly when complicated by macrophage activation syndrome (MAS).
Case Presentation: We report a 12-year-old girl presenting with a 10-day history of spiking fever and sore throat, accompanied by cracked lips, conjunctivitis, cervical lymphadenopathy, multiform erythematous rash, edema and desquamation of the hands, and arthralgia. Based on the clinical presentation, Kawasaki disease was suspected and treated with intravenous immunoglobulin (IVIG) and aspirin, followed by infliximab after an insufficient response. This resulted in resolution of fever and clinical improvement. After 48 hours, she again developed fever, worsening rash, and worsening of her joint complaints. Subcutaneous anakinra was started. Laboratory evaluation revealed a markedly elevated ESR (max. 128 mm/h), CRP (max. 95.8 mg/L), ferritin of initially 1575 ug/L (max 6379 ug/L) and interleukin-18 of >20,000 pg/ml, favoring a diagnosis of Still’s disease. Serial echocardiography showed no coronary artery dilatation or aneurysms. Following initiation of anakinra, the patient developed anemia and leukopenia, raising concern for MAS. High-dose methylprednisolone pulse therapy was commenced, leading to rapid clinical and laboratory recovery.
Discussion: Kawasaki disease mimics include bacterial and viral infections, or other autoinflammatory syndromes. Still’s disease shares several overlapping features with KD, such as prolonged fever, rash, arthritis and lymphadenopathy. However, extreme hyperferritinemia, elevated IL-18 levels, prominent arthritis, and cytopenias — especially in the setting of MAS — support Still’s disease over KD. Recognition of clinical mimics of KD or overlap syndromes are crucial, as management strategies may differ with a preference for anti-IL-1 treatment instead of TNF blockade. This case highlights the importance of reassessing the diagnosis in refractory or atypical KD presentations.
Conclusion: Still’s disease with MAS should be considered in children with KD-like features who show incomplete or transient response to standard KD therapy, particularly when inflammatory markers such as IL-18 are markedly elevated.