MPO and necrotizing vasculitis: Microscopic polyangiitis (MPA) is a rare, necrotizing vasculitis that primarily affects small-sized blood vessels, with a predilection for the upper and lower respiratory tract and the kidneys. It is commonly associated with the presence of perinuclear antineutrophil cytoplasmic antibodies (p-ANCA), often targeting myeloperoxidase (MPO), and typically presents with renal impairment, pulmonary symptoms, or systemic features such as fatigue and weight loss.