Pulmonary involvement in ANCA-associated vasculitis from the view of the pulmonologist

Microscopic polyangiitis (MPA), granulomatosis with polyangiitis (GPA), and eosinophilic granulomatosis with polyangiitis (Churg–Strauss syndrome) are conditions classified under the general heading of antinuclear cytoplasmic autoantibody (ANCA)-associated vasculitis (AAV). Lung lesion is a very common and important clinical feature in AAV. In MPA, diffuse alveolar hemorrhage and pulmonary fibrosis (PF) are the most frequent manifestations. High-resolution computed tomography (HRCT) chest findings associated with MPA in PF patients demonstrate a high frequency of usual interstitial pneumonia (UIP), fibrotic-nonspecific interstitial pneumonia (F-NSIP), and combined PF and emphysema (CPFE) pattern with honeycombing, traction bronchiectasis, ground-glass opacity, and emphysema. In most of these cases, the histologic pattern of PF has been classified as UIP and/or fibrotic NSIP. In addition, a high incidence of histological findings, such as extensive interstitial fibrosis, lymphoid hyperplasia, and bronchiolitis, are characteristics observed in PF associated with collagen vascular diseases and which are not observed in idiopathic PF (IPF). In some cases, PF precedes the development of MPA. Indeed, there are some cases of pulmonary-limited MPA in this group. Therefore, clinicians should be aware of MPA as an underlying feature of PF in order to avoid overlooking and misdiagnosing this condition as IPF. The median survival time (MST) in UIP pattern/MPA is comparable with that of IPF. In GPA, almost all patients have either upper airway or lower respiratory tract lesions. Solitary or multiple nodules (frequently cavitated) and masses are the most common findings on chest images. Asthma is a cardinal symptom of Churg-Straus syndrome, often preceded by allergic rhinitis. To induce remission, a severity-based regimen was given to patients according to the appropriate protocol of the Japanese patients with myeloperoxidase (MPO)-ANCA-associated vasculitis (JMAAV) study group: low-dose corticosteroid and, if necessary, cyclophosphamide or azathioprine in patients with mild form; high-dose corticosteroid and cyclophosphamide in those with severe form; severe-form regimen plus plasmapheresis in those with the most severe form.