Usual interstitial pneumonia following resolution of cavitated pulmonary masses in a patient with ANCA‐associated vasculitis

A 72‐year‐old woman with slight pulmonary interstitial reticular markings was initially diagnosed with microscopic polyangiitis (MPA). Two years later, cavitated pulmonary masses appeared, and a biopsy specimen revealed granulomas. Granulomatosis with polyangiitis (GPA) was diagnosed. The masses resolved with treatment. Ten years later, the usual interstitial pneumonia (UIP) pattern appeared on chest computed tomography (CT). The diagnosis of lung toxicity from methotrexate (MTX) or cyclophosphamide (CYC) was precluded by the clinical course. Despite treatment with prednisolone (PSL), the UIP progressed. The change of pulmonary pathology from masses to UIP is rare in patients with GPA.