[A case of IgG4-positive inflammatory pseudotumor which rapidly resolved].

A 72-year-old man visited our hospital due to persistent cough, fever and weight loss. A chest X-ray film revealed a round tumor in the left lower lung field. A specimen obtained by transbronchial lung biopsy demonstrated histiocytic and lymphocytic infiltration in the alveolar space, with spindle myofibroblasts and plasmacytes in the interstitium, Those findings were consistent with inflammatory pseudotumor. Four weeks later, a chest X-ray film showed only scars of the primary lesion, and his symptoms resolved dramatically. He has had no recurrence of symptoms and pulmonary tumor since then. Although spontaneous remission is uncommon in inflammatory pseudotumor of the lung, there are several case reports about spontaneous remission of hepatic inflammatory pseudotumor and autoimmune pancreatitis, parts of IgG4-related sclerosing disease. Recently, inflammatory pseudotumor is thought to be IgG4-related sclerosing disease. We speculate that IgG4 may be associated with spontaneous remission of inflammatory pseudotumor of the lung, and we discuss this issue in relation to the pertinent literature.