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Crystal-storing histiocytosis (CSH) is a rare disorder characterized by the accumulation of histiocytes laden with refractile intracytoplasmic crystals in various organ systems and is most commonly associated with an underlying plasma cell neoplasm or a B cell lymphoproliferative disorder.

We present the case of a 61-year-old man who underwent a bone marrow biopsy as part of work-up for anemia. The biopsy showed a markedly hypercellular bone marrow (95% cellular) with diffuse sheets of histiocytes replacing 80% of the marrow space (A-red arrow). The histiocytes exhibited abundant striated pink cytoplasm imparting a Gaucher-like appearance (B-red arrow). A few histiocytes showed intracytoplasmic refractile rhomboid as well as occasional tubular crystalline structures (B-green arrows). Scattered in between the histiocytes were subtle clusters of plasma cells comprising 10% of the marrow cellularity (A-green arrow). By immunohistochemistry, the plasma cells were CD138 and CD56 positive and kappa light chain restricted. Flow cytometric immunophenotyping performed on the bone marrow aspirate also revealed a kappa light chain restricted plasma cell population that was CD38+, CD138+, CD56+, CD19-, CD20-, and CD117+. Based on these findings a diagnosis of IgG kappa multiple myeloma with associated crystal-storing histiocytosis (CSH) was made.

Morphologically, CSH exhibits a wide spectrum with respect to the appearance of histiocytes and crystals. In aspirate specimens, the crystals within the histiocytes may exhibit bright eosinophilic, needle-like, or globular appearance whereas in hematoxylin and eosin-stained biopsy specimens the histiocytes show intracellular hexagonal, rhomboid, needle-like or globular, refractile inclusions [1]. In some instances, the histiocytic infiltration can be exuberant and may outnumber or mask a clonal plasma cell or B cell population, as in this case. The recognition of CSH and awareness of its strong association with plasma cell neoplasms and B cell lymphoproliferative disorders is crucial in order to avoid histologic misinterpretation.

Reference: 

1. Fang H, Chiu A, Reichard, K. Crystal-Storing Histiocytosis in Bone Marrow: A Clinicopathologic Study of Eight Cases and Review of the Literature, American Journal of Clinical Pathology. 2018;149:148–163.