Crystal-Storing Histiocytosis with Plasma Cell Neoplasm in the Setting of Chronic Carbamazepine Exposure

Crystal-storing histiocytosis (CSH) is an uncommon phenomenon in which crystalline material accumulates within the cytoplasm of histiocytes, and is typically associated with an underlying lymphoproliferative or plasma cell disorder with monoclonal immunoglobulin expression, such as multiple myeloma (MM), lymphoplasmacytic lymphoma (LPL), and monoclonal gammopathy of undetermined significance (MGUS).(1,2) With a few exceptions, the crystalline materials are almost exclusively composed of. immunoglobulin light chains.(2,3) Recently, other less common variants of CSH in which the crystalline material is not of an immunoglobulin origin have also been described, including clofazimine-induced CSH.(4,5) Here, we describe a case of CSH with plasma cell myeloma in the setting of chronic carbamazepine exposure.