Pulmonary immunocytoma with massive crystal storing histiocytosis: a case report with review of literature.

An unusual immunocytoma (lymphoplasmacytoid lymphoma) composed predominantly of sheets of globoid and spindle-shaped crystal-storing histiocytes was detected incidentally in the right lung of a 72-year-old woman. Scattered lymphoplasmacytic aggregates within the tumor had monoclonality with anti-kappa immunoglobulin (Ig) M antibodies. The crystals were outlined positively by the same antibodies. They stained an intense blue with phosphotungstic acid-hematoxylin (PTAH) and were found during electron microscopy to be membrane bound and also within type I pneumocytes and the extracellular space. Excessive production of kappa IgM by neoplastic low-grade lymphoplasmacytoid cells of B-cell origin in an altered intra- or extracellular milieu may lead to crystallization and phagocytosis by reactive histiocytes. Review of the literature revealed seven more cases: four in the head and neck, and one each in the skin, the lymph node, and the lung. IgM was the most frequently crystallizing immunoglobulin (four of seven) and all had kappa light chains. The lesion needs to be differentiated from neoplastic and nonneoplastic histiocytic and lymphoplasmacytic disorders. The difference with bronchial mucosa-associated lymphoid tissue lymphoma and marginal zone lymphoma is, perhaps, semantic.