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A 68-year-old woman was hospitalized for evaluation of progressive dyspnea, cough, and hemoptysis. She had a 2-month history of malaise, anorexia, arthralgias, and a 30-lb weight loss. Symptoms did not improve with outpatient antibiotic therapy. Laboratory studies were significant for profound anemia, elevated erythrocyte sedimentation rate (ESR), C-reactive protein (CRP), and decreased renal function. Perinuclear-pattern antineutrophil cytoplasmic antibody (p-ANCA) and myeloperoxidase (MPO) antibody were positive. Urinalysis showed microscopic hematuria with granular and red blood cell casts. Chest radiograph revealed bilateral alveolar infiltrates (Figure 79-1). Bronchoscopy with bronchoalveolar lavage was consistent with alveolar hemorrhage, and transbronchial lung biopsy showed changes of pulmonary capillaritis (Figure 79-2). An extensive infectious workup was negative. A diagnosis of microscopic polyangiitis (MPA) was made. The patient was treated with high-dose corticosteroids and oral cyclophosphamide, resulting in gradual clinical improvement. She was subsequently switched to azathioprine for maintenance of remission.
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MPA is a rare, multisystem autoimmune disorder.
It is characterized by inflammation of small blood vessels such as arterioles, venules, and capillaries.
It most commonly occurs in the 65- to 74-year age group.
Males are affected slightly more frequently than females.
Incidence of MPA is 3 to 6 per million per year; prevalence is about 60 per million population.1,2
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ETIOLOGY AND PATHOPHYSIOLOGY
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The exact etiology of MPA remains unknown.
Genetic and environmental factors, including infections, are thought to play a role in disease pathogenesis.
Antineutrophil cytoplasmic antibodies (ANCAs) are present in most patients with MPA and are specific for MPO, an antigen in neutrophil granules and monocyte lysosomes.
In vitro and experimental animal observations suggest that ANCAs have an important pathogenic role in the pathogenesis of MPA. However, other proinflammatory stimuli are required for the development of clinical disease.
Antiendothelial cell antibodies (AECAs) may also play a role in pathogenesis.
Histologically, MPA is characterized by necrotizing small vessel vasculitis (SVV) without evidence of granulomatous inflammation.2,3
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MPA mainly involves the kidney along with the upper and lower respiratory tract.
Symptoms are variable and related to pattern of involvement of the internal organs.
Constitutional symptoms including fever and weight loss are common.
Almost all patients have renal involvement, characterized by rapidly progressive glomerulonephritis, which may progress to end-stage kidney disease.
Pulmonary manifestations occur in about 50% of patients. Pulmonary capillaritis from MPA causes alveolar hemorrhage with hemoptysis, dyspnea, cough, and pleuritic chest pain. ...