A novel approach to diagnosing crystal-storing histiocytosis: utility of scanning electron microscopy for formalin-fixed paraffin-embedded tissue specimens

Crystal-storing histiocytosis (CSH) is a rare disorder that shows infiltration of histiocytes with an aberrant cytoplasmic accumulation of crystalline structures and is often accompanied by lymphoproliferative-plasma cell disorders (LP-PCD) as background diseases. The diagnosis of CSH requires identification of crystalline structures that accumulate in the infiltrating histiocytes, which may be challenging by optical microscopy alone. In this case report, we describe an atypical course of systemic CSH with multifocal fibrosclerosis of an unknown background disease that was diagnosed by ultrastructural observation, including transmission electron microscopy (TEM) and scanning electron microscopy (SEM), in pathological autopsy. In addition, crystalline structures were successfully identified by scanning electron microscopic observations using formalin-fixed and paraffin-embedded (FFPE) tissue from biopsy specimens taken before death. Since CSH was identified by SEM in a tiny biopsy specimen, observation of histiocytic infiltrative lesions by SEM using FFPE tissue may lead to early detection of and initiation of treatment for CSH.

Automated summary

Crystal-storing histiocytosis (CSH) is a rare disorder characterized by histiocyte infiltration and abnormal accumulation of crystalline structures, often occurring with lymphoproliferative-plasma cell disorders (LP-PCD) as background diseases. The diagnosis of CSH is challenging as optical microscopy alone may not be sufficient for identifying the crystals in infiltrating histiocytes. This case report highlights the atypical course of systemic CSH with multifocal fibrosclerosis, diagnosed through ultrastructural observation using transmission electron microscopy (TEM) and scanning electron microscopy (SEM) in pathological autopsy. Additionally, scanning electron microscopic observations using formalin-fixed and paraffin-embedded (FFPE) tissue from biopsy specimens before death successfully identified the crystalline structures. Early detection and treatment of CSH may be facilitated by SEM observation of histiocytic infiltrative lesions using FFPE tissue.