RESUMEN
One of the most frequent diffuse interstitial lung diseases is hypersensitivity pneumonitis. It is related to exposure to diverse antigens, causing fibrosis in advanced stages, making the differential diagnosis with interstitial pulmonary fibrosis difficult as it overlaps with the usual interstitial pneumonia pattern. On the other hand, there are interstitial lung diseases associated with ANCA, such as microscopic polyangiitis, which is also related to the usual interstitial pneumonia pattern. We present the case of a 74-year-old male patient with chronic dyspnea, history of smoking and exposure to organic particles, in addition to a pattern suggestive of moderately severe restriction. The diagnosis was confirmed by histology of hypersensitivity pneumonitis by presenting granules, however, anti MPO and p-ANCA positivity was found, integrating the simultaneous diagnosis of microscopic polyangiitis. This is a case of difficult diagnosis since these pathologies have not been previously reported to coexist.