[A case of bronchiolitis obliterans organizing pneumonia (BOOP) showing spontaneous regression after an open lung biopsy].

The patient was a 57-year-old Japanese male with dry cough, exertional dyspnea of 6 weeks' duration and bilateral basal pulmonary infiltrates, before a left thoracotomy for lung biopsy was performed in August 1984. Because the symptoms of the patient were not severe, he could be followed up without corticosteroid hormone treatment for 3.5 years, during which a spontaneous regression of both symptoms and objective findings were recognized, following the open lung biopsy. The primary pathological diagnosis of the case was an unclassified type of interstitial pneumonia, because the two lobes of the left lung showed diffuse alveolar septal fibrotic and inflammatory changes. However, granulation tissues in respiratory bronchioles were noted in tissue from the lingular segment and, after more careful observation, from the lower lobe (segment 8) (Fig. 9). Bacteriological cultures from fresh lung tissues were negative for microorganisms. From these clinical and pathological findings, this patient's pulmonary lesions were determined to be idiopathic BOOP.