Microscopic polyangiitis

Microscopic polyangiitis (MPA) is a rare systemic autoimmune disease classified as an anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis. It is characterized by necrotizing inflammation of small blood vessels (capillaries, venules, and arterioles) without granulomatous formation, distinguishing it from granulomatosis with polyangiitis (formerly Wegener's). MPA primarily affects the kidneys and lungs, though it can involve virtually any organ system including the skin, peripheral nerves, gastrointestinal tract, and musculoskeletal system. Most patients are positive for perinuclear ANCA (p-ANCA) directed against myeloperoxidase (MPO-ANCA). The hallmark renal manifestation is rapidly progressive glomerulonephritis (pauci-immune necrotizing and crescentic glomerulonephritis), which can lead to kidney failure if untreated. Pulmonary involvement frequently presents as alveolar hemorrhage, which can be life-threatening. Other common symptoms include constitutional features such as fever, weight loss, fatigue, and myalgias. Skin manifestations may include purpura, livedo reticularis, and skin ulcers. Peripheral neuropathy, particularly mononeuritis multiplex, occurs in a significant proportion of patients. Treatment of MPA typically involves two phases: induction of remission and maintenance therapy. Induction therapy generally consists of high-dose glucocorticoids combined with either cyclophosphamide or rituximab. Plasma exchange may be considered in patients with severe renal disease or pulmonary hemorrhage. Maintenance therapy commonly uses rituximab or azathioprine to prevent relapse. Avacopan, a complement C5a receptor inhibitor, has been approved as an adjunctive treatment. Despite advances in therapy, MPA carries significant morbidity related to both the disease itself and treatment-related side effects, and relapses are common, necessitating long-term monitoring.

Data sourced from FDA regulatory filings and ClinicalTrials.gov. Updated periodically.

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