Lung Involvement in ANCA-Associated Vasculitis

The small vessel vasculitis syndromes, granulomatosis with polyangiitis (GPA), microscopic polyangiitis (MPA), and eosinophilic polyangiitis (EGPA) comprise the group referred to cumulatively as antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV). The respiratory tract is commonly involved in each of the syndromes. The clinical presentation of pulmonary parenchymal and tracheobronchial inflammation of GPA and MPA is quite heterogeneous. Consequently, the differential diagnosis is broad and includes infection, malignancy, and other autoimmune diseases. Necrotizing granulomatous inflammation is the disease-defining feature of GPA causing lung nodules or mass lesions with or without cavitation, as well as tracheobronchial inflammation, often with subsequent stenosis. Capillaritis presenting clinically as diffuse alveolar hemorrhage is a severe disease manifestation often leading to respiratory failure which occurs in about 25% of patients with GPA or MPA, but is rare in patients with EGPA. MPA with ANCA targeting myeloperoxidase (MPO-ANCA) is sometimes associated with interstitial lung disease, a relationship that remains under investigation. The diagnostic approach for specific clinical presentations is described in this chapter. The disease manifestations caused by active inflammation in the respiratory tract usually responds well to immunosuppressive therapy following standard principles for AAV. However, damage caused by tracheobronchial involvement may require individualized interventions such as dilation procedures or stent placement. The management of diffuse alveolar hemorrhage caused by AAV is discussed in light of recent study results, and a practical approach to patients with interstitial lung disease and MPO-ANCA is proposed.