From Cough to Myocarditis: A Systemic Tale of Adult-Onset Still's Disease.

Adult-onset Still's disease (AOSD) is a rare systemic autoinflammatory disorder that presents a significant diagnostic challenge due to its nonspecific features and overlap with infectious, autoimmune, and malignant conditions. We report a case of a 39-year-old man who initially presented with fever, sore throat, myalgia, and cough. He was initially treated for a presumed respiratory infection. On re-presentation, he developed worsening pyrexia, polyarthritis, odynophagia, and dyspnea. Laboratory investigations revealed markedly elevated inflammatory markers, hyperferritinemia exceeding 6000 µg/L, neutrophilic leukocytosis, anemia, thrombocytopenia, and deranged liver function tests. Imaging demonstrated splenomegaly and pleural effusion, while elevated troponin and ECG changes were consistent with myocarditis. Extensive infectious, autoimmune, and malignant evaluations were unrevealing, and despite broad-spectrum antibiotics, his symptoms persisted. Given the constellation of prolonged fever, systemic inflammation, arthritis, hyperferritinemia, and exclusion of alternative causes, a diagnosis of AOSD was made. The patient responded dramatically to high-dose corticosteroid therapy, with rapid resolution of fever and arthritis and significant biochemical improvement. This case underscores the importance of recognizing AOSD in patients with prolonged pyrexia of unknown origin, particularly when ferritin levels are markedly elevated, and highlights how systemic features such as cardiac and serosal involvement may indicate severe disease. Early initiation of corticosteroids is critical, as timely treatment can lead to rapid recovery and help prevent life-threatening complications such as macrophage activation syndrome.