B35-17 Adult-onset Still’s Disease Presenting With Myocarditis - An Uncommon But Potentially Lethal Complication

Abstract Introduction Adult-onset Still’s disease (AOSD) is a rare autoimmune inflammatory disorder characterized by a triad of fever, polyarthritis, and salmon-pink evanescent rash. Myocarditis represents an uncommon but potentially lethal complication. We present the case of a 20-year-old female presenting with shock secondary to myocarditis due to AOSD. Case Presentation A 20-year-old female with no medical or family history presented with a 3-day history of chest pain, shortness of breath, multiple joint pain, rash and fever. On admission, she was febrile (T max 100.4 °F), tachycardic, hypotensive (70/50 mmHg), tachypneic (25/min) and saturating well on room air. Cardiovascular examination revealed normal heart sounds without murmurs, jugular venous distension or edema. Laboratory tests showed anemia (hemoglobin 8.9 g/dL), leukocytosis (22 × 10³/μL), thrombocytosis (585 × 10³/μL), lactic acidosis (6.8 mmol/L), elevated ferritin (16,500 ng/mL), and beta-natriuretic peptide (12,252 pg/mL). Electrocardiogram showed sinus tachycardia and right axis deviation without any acute ST-T changes. Patient was appropriately resuscitated, cultured, started on pressors and broad spectrum antibiotics. All infective, autoimmune and vasculitis work-up was negative. Echocardiogram showed severe left ventricular systolic dysfunction (30%) with preserved right-sided function. A pyrophosphate scan excluded amyloidosis. Cardiac magnetic resonance imaging (MRI) revealed myocardial edema and late gadolinium enhancement (Fig 1), confirming acute myocarditis. A diagnosis of AOSD was established based on Yamaguchi criteria. The patient improved with corticosteroid therapy and subsequently discharged. Discussion Cardiac involvement in AOSD (AOSD-C) is uncommon with one study estimating 29% cardiac involvement and 6% with myocarditis. It confers worse prognosis and higher intensive care unit admission rates. Common presenting features include fever, pharyngitis, arthritis, and rash. Predictors of cardiac involvement include high C-reactive protein, chest pain, dyspnea, leukocytosis and markedly elevated ferritin. Echocardiography may reveal reduced ejection fraction, while cardiac MRI demonstrates edema and late gadolinium enhancement. Endomyocardial biopsy may be reserved for uncertain cases. High-dose corticosteroids are first-line therapy. Refractory cases may benefit from intravenous immunoglobulin, methotrexate, or biologic therapy. Interleukin-1(IL-1) inhibition with anakinra and interleukin-6 (IL-6) inhibition with tocilizumab have shown favorable outcomes in steroid-resistant disease. Conclusion AOSD may rarely present as acute myocarditis in young adults. Clinicians should suspect AOSD in patients with fever, rash, arthritis, leukocytosis, and hyper-ferritinemia. Prompt diagnosis and immunosuppressive therapy, beginning with corticosteroids and escalating to IL-1 or IL-6 inhibitors when necessary, are crucial to improve outcomes. This abstract is funded by: HCA Healthcare