Immunoglobulin crystal-storing histiocytosis in a pleural effusion from a woman with iga kappa multiple myeloma: a case report

Background Crystal-storing histiocytosis (CSH) is a rare disorder occurring in patients with lymphoproliferative diseases, predominantly multiple myeloma and low grade B-cell lymphoma. This report presents the first case of CSH diagnosed on pleural fluid from a patient with multiple myeloma (MM). Case A 79-year-old woman with IgA k MM underwent thoracocenthesis and thoracic drainage because of a pleural effusion. Cytologic and immunocytochemical examination of pleural fluid revealed abundant histiocytic, CD68-positive cells with prominent intracytoplasmic, needlelike, crystalloid inclusions showing strong immunopositivity for IgA heavy and k light chains. Identical crystals were observed on an extracellular background. No myeloma infiltration was detected. Two weeks later, examination of new pleural fluid from the patient showed a similar cytologic picture, but, in addition, isolated plasma cell features were identified. They were too few for a meaningful determination of clonality. The patient died 1 month after the CSH diagnosis. Conclusion This case illustrates the value of cytologic examination of serous fluids from patients with plasma cell dyscrasias, not only to evaluate possible infectious or neoplastic causes but also to diagnose CSH