Crystal‐storing histiocytosis: a clinicopathological study of 13 cases

Aims Crystal-storing histiocytosis (CSH) is a rare lesion composed of histiocytes with abnormal intralysosomal accumulation of immunoglobulin (Ig) as crystals, reported in patients with plasmacytic/lymphoplasmacytic neoplasms. The aims of this study were to report the clinicopathological features of 13 patients with CSH, and to describe the proteomic composition of the crystals in three cases analysed by mass spectrometry (MS). Methods and results There were seven men and six women, with a median age of 60 years (range, 33–79 years). CSH was generalized in one patient (8%) and localized in 12 (92%) patients, involving various sites. CSH was associated with a low-grade B-cell lymphoma with plasmacytoid differentiation or a plasma cell neoplasm in all cases. In 10 (77%) cases, CSH represented >50% of the neoplastic infiltrate. According to immunohistochemical studies, histiocytes were positive for monotypic kappa in 5 (50%) cases, and for monotypic lambda in 4 (40%) cases; in 1 (10%) case, the results were equivocal. MS analysis of the histiocyte contents in all three tested cases showed a predominance of variable-region fragments of Ig light and/or heavy chains. Conclusions CSH is frequently associated with an underlying lymphoplasmacytic neoplasm. MS findings suggest that Ig alterations and/or possibly defects in the ability of histiocytes to process Ig play a role in pathogenesis.