Reactive eosinophilic pleuritis. A sequela of pneumothorax in pulmonary eosinophilic granuloma.

Pneumothorax is a frequent complication of pulmonary eosinophilic granuloma (EG) and can be a presenting manifestation of this disorder. Histologically the differential diagnosis of EG in patients presenting with pneumothorax includes reactive eosinophilic pleuritis (REP), a nonspecific inflammatory reaction commonly observed in association with ruptured pleural blebs. The authors present a case in which both EG and REP were found in lung tissue from a patient with recurrent pneumothorax. Immunohistochemical stains for lysozyme and S-100 protein assisted in differentiating these two lesions. Histiocytic cells in areas of EG were S-100 positive and lysozyme negative, whereas mononuclear cells in areas of REP were S-100 negative and lysozyme positive. It is emphasized that the finding of REP and pleural blebs in lung tissue from patients presenting with pneumothorax does not exclude the diagnosis of EG.