Microscopic polyangiitis

This code represents microscopic polyangiitis, a systemic autoimmune disease characterized by necrotizing inflammation of small blood vessels (capillaries, venules, or arterioles) without immune complex deposition. It commonly affects the kidneys, lungs, and skin, leading to conditions like rapidly progressive glomerulonephritis and pulmonary hemorrhage.

Use this code when documentation explicitly states a diagnosis of microscopic polyangiitis. This diagnosis is typically confirmed through biopsy showing pauci-immune necrotizing vasculitis and positive ANCA (anti-neutrophil cytoplasmic antibody) serology, particularly p-ANCA/MPO-ANCA.

• Differentiate carefully from polyarteritis nodosa (M30.0), which is an Excludes1 condition and involves medium-sized arteries.
• Ensure documentation specifies "microscopic" polyangiitis to avoid confusion with other forms of vasculitis.
• Code any associated organ manifestations (e.g., glomerulonephritis, pulmonary hemorrhage) as secondary diagnoses.