Massive bone marrow crystal-storing histiocytosis in a patient with IgA-lambda multiple myeloma and extensive extramedullary disease. A case report.

We report a case of multiple myeloma (MM) displaying an unusual course, with metastatic spread in uncommon sites (gastroduodenal and upper respiratory tract, breast, skin and liver) and with a fatal outcome. In our patient this plasma cell neoplasm was associated with a rare condition named crystal-storing histiocytosis (CSH), resulting from the storage in reactive histiocytes of crystalline immunoglobulin inclusions. These crystal-forming paraprotein components are secreted by the neoplastic plasma cells and give rise to the crystalline material of the histiocytes only after their ingestion and degradation by the same histiocytes. In this disorder crystal-storing cells may be present in various tissues (in our case mainly in bone marrow), often with functional alterations of the involved organs. In our opinion the association of this "atypical" MM with CSH is to be considered an uncommon event.