Respiratory System Involvement in Antineutrophil Cytoplasmic-associated Vasculitides: Clinical, pathological, radiological and therapeutic considerations

Wegener's granulomatosis (WG), microscopic polyangiitis (MPA) and Churg- Strauss syndrome (CSS) are small-vessel vasculitides that, because of their frequent association with antineutrophil cytoplasmic antibodies (ANCA), are usually referred to as ANCA-associated systemic vasculitides (AASV). The diagnosis of AASV is made on the basis of clinical findings, biopsy of an involved organ and the presence of ANCA in the serum. Lung disease is a very common and important clinical feature of AASV. In WG, almost all patients have either upper airway or lower respiratory tract disease. Solitary or multiple nodules, frequently cavitated, and masses are the most common findings on chest radiography. Asthma is a cardinal symptom of CSS, often preceded by allergic rhinitis. Pulmonary transient and patchy alveolar infiltrates are the most common radiographic findings. In MPA, diffuse alveolar haemorrhage as a result of alveolar capillaritis is the most frequent manifestation of respiratory involvement, and is clinically expressed as haemoptysis, respiratory distress and anaemia. However, diffuse alveolar haemorrhage may also be subclinical and should be suspected when a chest radiograph demonstrates new unexplained bilateral alveolar infiltrates in the context of falling haemoglobin levels. Normal and high-resolution CT have a higher sensitivity than chest radiography for demonstrating airway, parenchymal and pleural lesions. However, many of these radiological findings are nonspecific and, therefore, their interpretation must take into account all clinical, laboratory and pathological data. Therapy of AASV is commonly divided into two phases: an initial 'remission induction' phase, in which more intensive immunosuppressant therapy is used to control disease activity, and a 'maintenance' phase, which uses less intensive therapy, for maintaining disease remission while lowering the risk of adverse effects of immunosuppressant drugs. In patients with AASV refractory to standard therapy with corticosteroids and oral cyclophosphamide, new therapeutic options are now available. Recurrence of pulmonary symptoms suggesting a flare indicates the need for a careful search for an opportunistic lung infection or iatrogenic pulmonary complications. In conclusion, involvement of the respiratory system is a very common and important organ manifestation of AASV. Respiratory system involvement comprises a wide spectrum of clinical features and radiological findings, and because of its frequency and prognostic significance, a complete assessment of the respiratory system should be included in the work-up of all patients with AASV.