Epidemiology and management of interstitial lung disease in ANCA-associated vasculitis

Antineutrophil cytoplasmic antibodies (ANCA)-associated vasculitis (AAV) is a group of systemic vasculitides that predominantly affect small vessels, including granulomatosis with polyangiitis (GPA), microscopic polyangiitis (MPA), and eosinophilic granulomatosis with polyangiitis (EGPA). Pulmonary involvement is frequently observed in AAV patients, with various possible phenotypes in the different diseases. In the last years, among the possible types of lung involvement, a growing interest has been addressed to the interstitial lung disease (ILD). Prevalence of ILD is higher in MPA than in GPA; in fact, ILD has been reported in up to 45% of MPA patients and in 23% of GPA. Anti-MPO antibodies are the main ANCA subtype associated to ILD, in about 46-71% of cases, while anti-PR3 antibodies are reported in 0-29% of patients. High resolution computed tomography (HRCT) frequently detects interstitial lung abnormalities in AAV, up to 66% of patients with MPA, even if with an unclear clinical relevance, specifically in asymptomatic patients. Ground glass opacities, mainly consistent with diffuse alveolar hemorrhage (DAH), are the most frequent finding in MPA patients, but reticulations, interlobular septal thickening and honeycombing are also reported. ILD significantly affects quality of life and survival, with mortality increased 2 to 4 times, particularly higher in MPA patients with pulmonary fibrosis. Currently, immunosuppressive therapy is considered also as a possible treatment of ILD. However, a careful evaluation of progression and severity of lung involvement, should guide the treatment decision in the single patient. In this review, we discuss the available evidence on clinical features, diagnostic work-up, prognosis and management of AAV-ILD.