OBJECTIVE. The lung is one of the organs possibly involved in microscopic polyangiitis (MPA), and myeloperoxidase (MPO) antineutrophil cytoplasmic antibody (ANCA) is commonly found in patients with MPA. The aim of this study was to assess pulmonary lesions in Japanese patients with MPA. SUBJECTS AND METHODS. This prospective study was based on 144 patients with MPA who were enrolled in the Remission Induction Therapy in Japanese Patients With ANCA-Associated Vasculitis and Rapidly Progressive Glomerulonephritis Study and who underwent chest high-resolution CT (HRCT) imaging at the time of diagnosis during 2011-2014. We reviewed the electronic case report forms of patients with MPA who did and did not have interstitial pneumonia (IP), and the clinical features and laboratory findings of these groups were compared. RESULTS. Abnormal HRCT findings were noted in 134 of the 144 patients (93%). Chest HRCT findings included ground-glass opacity (n = 72; 50%), reticulation (n = 69; 48%), traction bronchiectasis (n = 57; 42%), honeycombing (n = 44; 31%), and emphysema (n = 32; 22%). IP was diagnosed radiologically in 74 patients (51%), 38% of whom had the usual IP (UIP) pattern. Ground-glass opacity, reticulation, traction bronchiectasis, honeycombing, and interlobular septal thickening were frequent in patients with IP (p < 0.05). Patients with MPA with the UIP or possible UIP pattern also had minor findings, such as bronchial wall thickening, consolidation, increased attenuation around honeycombing, and traction bronchiectasis. CONCLUSION. IP (51%) was most commonly observed in Japanese patients with MPA, and 38% of these patients exhibited a UIP pattern. Increased attenuation around honeycombing or traction bronchiectasis was also found.

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