Pericardial Effusion as an Early Manifestation of Myeloperoxidase (MPO)-Positive Antineutrophil Cytoplasmic Antibody (ANCA)-Associated Vasculitis With Eosinophilia

Antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) is a rare but life-threatening autoimmune disease that primarily targets the kidneys and lungs. Cardiac involvement is far less common, and when it does occur, it is often overlooked until late in the disease course. We describe an elderly man who presented with acute breathlessness, pericardial effusion, eosinophilia, and worsening renal function. Initial management of pneumonia proved ineffective, and further investigation revealed strongly positive myeloperoxidase (MPO)-ANCA antibodies. The diagnosis of MPO-positive AAV with eosinophilia was established. Following treatment with corticosteroids and rituximab, the patient showed complete resolution of the effusion and significant recovery of renal function. This case highlights the diagnostic challenge of pericardial effusion as an early clue to systemic vasculitis and underscores the importance of early recognition and prompt immunosuppressive therapy.