Pulmonary extranodal marginal zone lymphoma with massive crystal storing histiocytosis.

We present an incidentally discovered, unusual case of pulmonary bronchial mucosa-associated lymphoid tissue lymphoma associated with massive crystal storing histiocytosis in a 69-year-old woman. The neoplastic process was masked by large numbers of epithelioid and spindled histiocytes containing crystalline material. Histochemical stains showed intracytoplasmic crystals and immunoperoxidase staining confirmed the histiocytic nature of the swollen cells. Electron microscopy demonstrated the characteristic appearance of immunoglobulin crystals. Lymphoepithelial lesions were identified on immunohistochemical staining, compounding suspicions of an underlying lymphoid neoplasm. Molecular studies later revealed a monoclonal B-cell population. The patient had no systemic evidence of a paraproteinemia. Crystal storing histiocytosis is a rare phenomenon in which macrophages accumulate light chain or immunoglobulin crystalline inclusions. The disease may be systemic, or localized as in this case. It is usually associated with the excess production of a monoclonal immunoglobulin, although there have been many case reports without this feature. An overview of crystal storing histiocytosis is given.