musculoskeletal and connective tissue disorders
Microscopic Polyangiitis (MPA)
Diagnosis of MPA
Clinical findings Tests for antineutrophil cytoplasmic antibodies and routine laboratory tests Biopsy Microscopic polyangiitis should be suspected in patients who have unexplained combinations of fever, weight loss, arthralgias, abdominal pain, alveolar hemorrhage, new-onset nephritic syndrome, new-onset multiple mononeuropathy, or polyneuropathy. Laboratory tests and sometimes x-rays are done, but the diagnosis is usually confirmed by biopsy. Tests include complete blood count , erythrocyte sedimentation rate (ESR), C-reactive protein, urinalysis, serum creatinine, and tests for antineutrophil cytoplasmic antibodies (ANCA). ESR, C-reactive protein levels, and white blood cell and platelet counts are elevated, reflecting systemic inflammation. Anemia of chronic disease is common. An acute drop in hematocrit suggests alveolar hemorrhage or hemorrhage in the gastrointestinal tract. Urinalysis (to check for hematuria, proteinuria, and cellular casts) should be done, and serum creatinine should be measured periodically to check for renal involvement. Immunofluorescence staining can detect ANCA; this test is followed by an enzyme-linked immunosorbent assay (ELISA) to check for specific antibodies. At least 60% of patients are ANCA-positive, usually perinuclear ANCA (p-ANCA) with antibodies against myeloperoxidase. Biopsy of the most accessible involved tissue should be done to confirm vasculitis. Renal biopsy may detect focal segmental pauci-immune necrotizing glomerulonephritis with fibrinoid necrosis of the glomerular capillary wall, leading to formation of cellular crescents. In patients with respiratory symptoms, chest imaging is done to check for infiltrates. Bilateral patchy infiltrates suggest alveolar hemorrhage even in patients without hemoptysis. CT is much more sensitive than x-ray. If patients have dyspnea and bilateral infiltrates, bronchoscopy should be done immediately to check for alveolar hemorrhages and to exclude infection. Blood coming from both lungs and all bronchi, with more blood coming as the bronchoscope goes deeper in the airways, indicates active alveolar hemorrhage. Hemosiderin-laden macrophages appear within 24 to 72 hours after onset of hemorrhage and may persist for up to 2 months. 