[A case of non-secretory myeloma with crystal-storing histiocytosis]

Crystal-storing histiocytosis (CSH) is a rare event observed in association with lymphoproliferative diseases, and mainly occur in plasma cell dyscrasias. It is presumed to be an intra-lysosomal accumulation of the secreted paraproteins. Crystal formation can be seen inside histiocyte-like cells with phagocytosed crystalline inclusions in the bone marrow and extramedullary sites. CSH is a rare morphological entity with poor prognostic implications and may be confused with Gaucher or pseudo-Gaucher cells. Herein we report a case of non-secretory myeloma associated with CSH showing a poor clinical course. A 79-yr-old male presenting with dizziness was evaluated in hematology department for anemia. Laboratory tests revealed Hb of 4.9 g/dL and β2-microglobulin of 21,000 ng/mL (reference range, 0-370). Presence of monoclonal protein was not detected on protein electrophoresis and immunofixation in serum and urine. However, serum free light chain assay showed an increased kappa-light chain level of 126 mg/L (reference range, 3.3-19.4) resulting in an increased kappa/lambda ratio. The bone marrow touch print showed numerous plasma cells and crystal-laden histiocytes and immunohistochemical stainings on bone marrow biopsy revealed positivity for CD38, CD56 and kappa in the plasma cells and CD68 and kappa in crystal-laden histiocytes.