Microscopic polyangiitis with pulmonary involvement: Case Report.

INTRODUCTION: ANCA-associated vasculitis is a rare autoimmune disorder characterized by necrotizing inflammation of small vessels, frequently affecting the kidneys and lungs, and may present as a potentially life-threatening pulmonary-renal syndrome during disease relapse. CASE PRESENTATION: We present the case of a 66-year-old woman with a history of MPO-ANCA-associated vasculitis with prior renal and pulmonary involvement, who was admitted with acute respiratory failure and rapidly progressed to severe acute respiratory distress syndrome requiring invasive mechanical ventilation, along with acute kidney injury (KDIGO stage 3B) superimposed on chronic kidney disease. Laboratory findings revealed progressive anemia, elevated inflammatory markers, and markedly increased MPO-ANCA titers, compatible with vasculitis reactivation presenting as diffuse alveolar hemorrhage and pulmonary-renal syndrome. The patient was treated with pulse methylprednisolone, intravenous immunoglobulin, plasmapheresis, and rituximab, in addition to intensive supportive care. Her clinical course was complicated by a urinary tract infection caused by extended-spectrum beta-lactamase (ESBL)-producing Escherichia coli. After gradual immunomodulatory treatment, she showed progressive recovery of respiratory and renal function, with resolution of the alveolar hemorrhage and satisfactory discharge from the intensive care unit. CONCLUSION: This case highlights the diagnostic challenges and severity of MPO-ANCA vasculitis relapse, and underscores the importance of early recognition, prompt immunosuppressive therapy, and multidisciplinary management to improve outcomes, especially in healthcare settings with limited resources.