Hemoptysis Revealing Microscopic Polyangiitis: A Case Report.

Microscopic polyangiitis (MPA) is a rare, necrotizing vasculitis affecting small-caliber vessels, commonly associated with anti-neutrophil cytoplasmic antibodies (ANCA), particularly anti-myeloperoxidase (MPO). We report the case of a 63-year-old male with a medical history of chronic smoking and hypothyroidism, who presented with hemoptysis, worsening dyspnea, and constitutional symptoms. Imaging revealed bilateral alveolo-interstitial infiltrates indicative of lung involvement, along with a distal pulmonary embolism. Laboratory investigations found anemia, rapidly progressive renal impairment, and positive anti-MPO perinuclear anti-neutrophil cytoplasmic antibodies (p-ANCA) at high titers, supporting a diagnosis of MPA. The patient was treated with high-dose corticosteroids and cyclophosphamide, with the immunosuppressive therapy adjusted according to his renal function. This case highlights the importance of considering MPA in patients with unexplained pulmonary and renal manifestations, especially in the presence of constitutional symptoms and positive ANCA serology.