Pulmonary infiltration with eosinophilia complicated with mucosa-associated lymphoid tissue lymphoma: A case report.

Tissue eosinophilia is rarely observed in cases of non-Hodgkin's lymphoma of B cell origin. The present study describes a rare case of mucosa-associated lymphoid tissue (MALT) lymphoma, which was initially misdiagnosed as eosinophilic pneumonia. The initial diagnosis was formed based on the results of chest radiography, peripheral eosinophilia tests and bronchoalveolar lavage, and the clinical course of the patient. Following administration of methylprednisolone (40 mg/day) for 4 days and oral administration of prednisolone (30 mg/day), the clinical course rapidly improved and the eosinophil count immediately decreased a to normal level. However, abnormal shadows observed on computed tomography (CT) scans of the chest did not diminish. At 6 months after the initiation of treatment, CT-guided percutaneous lung biopsy was performed, and a final diagnosis of primary pulmonary mucosa-associated lymphoid tissue lymphoma was made based on immunohistochemical examination. Primary lung MALT lymphoma remains a rare entity, with an indolent course and a reasonably favorable prognosis, whose diagnosis may be challenging.