Beyond Infection and Lupus Flare: MPO‐ANCA Microscopic Polyangiitis Causing Diffuse Alveolar Hemorrhage in a Patient With Systemic Lupus Erythematosus

We describe an elderly woman with systemic lupus erythematosus (SLE) who presented with dyspnoea, anemia, and bilateral pulmonary infiltrates initially diagnosed as community-acquired pneumonia. Despite appropriate antibiotics, she failed to improve, and all microbiological investigations remained negative. Further immunological evaluation revealed perinuclear antineutrophil cytoplasmic antibody (p-ANCA) with anti-myeloperoxidase (MPO) specificity, establishing a diagnosis of microscopic polyangiitis (MPA) complicated by diffuse alveolar hemorrhage (DAH). This case illustrates a complex diagnostic dilemma in which pulmonary hemorrhage in a patient with SLE may represent either lupus-related pulmonary vasculitis or a new ANCA-associated process. It highlights the importance of reconsidering the diagnosis in non-resolving respiratory disease, particularly in patients with overlapping autoimmune conditions.