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PATIENT STORY

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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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FIGURE 79-1

Chest radiograph showing bilateral alveolar infiltrates due to pulmonary hemorrhage.

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FIGURE 79-2

Photomicrograph from a transbronchial lung biopsy specimen demonstrates pulmonary capillaritis with acute and organizing intra-alveolar hemorrhage. Neutrophilic infiltrate and hemosiderin-laden macrophages are seen.

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EPIDEMIOLOGY

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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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DIAGNOSIS

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Clinical Features

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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 ...

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