Giant myeloma cells or crystal‐storing histiocytes?

A 77-year-old male with a 7-year history of IgG-κ (IgG kappa) multiple myeloma presented with chest pain; white blood cell count of 3.1 × 109/L; haemoglobin concentration of 100 g/L; platelet count of 235 × 109/L; serum total protein of 62.2 g/L, globulin of 34.1 g/L; serum creatinine of 87 μmol/L; and serum calcium of 2.00 mmol/L. The blood film showed 1% plasma cells. Bone marrow aspirate films showed 10% abnormal giant cells with intracytoplasmic Auer rod-shaped inclusions or abundant irregular purple inclusions (left, Wright–Giemsa stain, 10 × objective; middle-right, 100 × objective) and 85% myeloma cells. There was diagnostic uncertainty as to the lineage of these cells, with giant plasma cells as part of myeloma or crystal-storing histiocytes being possibilities. Flow cytometric analysis showed that 73.56% myeloma cells were positive for CD38, CD138, CD56, CD9 (dim), CD117 and cKappa while negative for CD45, CD19, CD20, CD27, CD28, CD33, CD81 and cLambda. Crystal-storing histiocytosis (CSH) is a rare, non-neoplastic histiocytic proliferation characterised by the accumulation of histiocytes containing intracytoplasmic crystalline immunoglobulin inclusions, typically kappa light chains, and is most commonly associated with underlying lymphoproliferative or plasma cell disorders.1-3 Histiocytes in crystal-storing histiocytosis are characterized by abundant eosinophilic cytoplasm containing elongated, needle-like or globular crystalline inclusions that are typically non-refractile and non-polarizable in bone marrow aspirates.3-6 Finally, the diagnosis was established as myeloma with CSH. The authors declared that this study received no financial support. This study did not involve personal information; only laboratory data were reported. Patient consent was, therefore, waived by the Ethics Committee of The First Hospital of Qinhuangdao.