[Inflammatory pseudotumor of the lung].

The patient was a 76-year-old man whose chief complaint was a dry cough. His chest X-ray film revealed a large hazy shadow with unclear margin in the left upper lobe. Bronchiolitis obliterans organizing pneumonia was initially diagnosed because transbronchial lung biopsy (TBLB) specimens showed organizing pneumonia with no evidence of malignancy. However, because the hazy shadow increased gradually in size despite steroid therapy. TBLBs were performed several more times to confirm the diagnosis. The last TBLB specimen showed proliferation of fibroblasts and mononuclear cells, with marked infiltration mainly of plasma cells 12 months after the initiation of steroid therapy. Because we were unable to obtain a histological diagnosis by bronchofiberscopy, a left upper lobectomy was preformed and the lesion resected. Histology disclosed inflammatory pseudotumor of a lymphoplasmacytic type with organizing pneumonia. The results of an immuno-histochemical examination confirmed that the proliferating plasma cells were polyclonal. These findings suggest that inflammatory pseudotumors should be taken into account by differential diagnoses of cases of organizing pneumonia that are resistant to steroid therapy.