Here, we present a 22-year-old female patient with adult-onset Still's disease (AOSD) who was newly diagnosed in the setting of secondary macrophage activation syndrome (MAS), a rare, life-threatening inflammatory disease with 50% mortality due to multi-organ failure. She met the diagnostic criteria of AOSD and MAS, while genetic testing excluded primary causes of MAS. She had high fevers, anemia, thrombocytopenia, splenomegaly, hematophagocytosis, and elevated serum ferritin (37,950 ng/mL) and CD25 levels (11,870 pg/mL), which remained unresponsive to corticosteroids and anakinra. Her serum interferon gamma (IFN-γ) levels were elevated (7 pg/mL). She was markedly responsive to IFN-γ blockade with emapalumab that eliminated her fevers and all MAS-associated laboratory abnormalities. This report provides initial evidence for therapeutic efficacy for IFN-γ blockade in AOSD and secondary MAS.

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A 42-year-old woman with juvenile idiopathic arthritis was treated with anakinra, corticosteroids, and hydroxychloroquine when she developed chronic hypoxic respiratory myopathy. She was admitted to the intensive care unit for acute hypercapnic respiratory failure and required prolonged intubation, subsequent tracheostomy, and long-term ventilatory support due to multiple failed spontaneous breathing trials after discontinuation of anakinra and steroids. Muscle biopsy revealed type II fiber atrophy with the accumulation of autophagosomes and vacuoles presenting as curvilinear bodies, elevated MHC class I antigen expression, and infiltration by CD68+ macrophages and CD8+ T cells. Type II fiber atrophy was attributed to corticosteroid use and curvilinear bodies due to blockade of autophagy by hydroxychloroquine. After hydroxychloroquine was discontinued, the patient recovered to her prehospitalization baseline.

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