Crystal-Storing Histiocytosis: Report of a Rare Case Presenting With Pathological Fracture of Femur. Is There More to the Entity?

Crystal-storing histiocytosis (CSH) is a rare histiocytic lesion, most often described in association with lymphoid malignancies, especially plasma cell myeloma or lymphomas associated with monoclonal gammopathy. A few cases have also been described in patients without an underlying lymphoid/plasmacytic neoplasm. The histiocytes are characterized by intralysosomal accumulation of crystals composed of whole or part of the immunoglobulin molecule. The pathobiology is largely unclear. It is a rare phenomenon and the available literature is restricted to case reports and a few case series. We present a case of a 70-year-old gentleman who presented with pathological fracture of left neck of femur secondary to CSH, a presentation so far unreported in the literature. Because of associated clinical features, a plasma cell dyscrasia was suspected and the workup, including bone marrow biopsy, yielded a diagnosis of plasma cell myeloma. Histological examination of the excised femoral head showed near complete replacement of the marrow spaces with sheets of histocytes rich in intracytoplasmic crystals and only occasional plasma cells. The peculiar presentation with pathological fracture of femur in the index case and predominant tumefactive lesions in the cases in the literature might suggest a possible neoplastic origin of this lesion.