Abstract
Crystal-storing histiocytosis (CSH) is a rare condition characterized by cytoplasmic accumulation of crystalline or granular material, typically immunoglobulins, within histiocytes. Most reported cases to date occurred in patients with a lymphoplasmacytic neoplasm such as lymphoplasmacytic lymphoma, monoclonal gammopathy of uncertain significance, multiple myeloma, or others. About 10% of cases are instead associated with non-neoplastic disorders including inflammatory bowel disease and rheumatoid arthritis. Primary cutaneous involvement is very uncommon with less than 10 cases reported to date, all of which have been associated with lymphoplasmacytic neoplasms. We present the case of a 44-year-old female with a 2-year history of a nasal lesion diagnosed as granular cell tumor (GCT) by an outside pathologist. She underwent slow Mohs due to increasing growth of the lesion. On histopathology, there is a variably dense dermal infiltrate of histiocytoid cells with granular cytoplasms, numerous plasma cells containing abundant cytoplasmic immunoglobulin and scattered lymphocytes. By immunohistochemistry, the histiocytoid cells stain positive for CD68 and CD163 and negative for S100. These findings support a histiocytic infiltrate over GCT. The cytoplasmic granules within histiocytes stain positive for kappa light and IgG heavy chains and negative for IgA, IgM and lambda compatible with CSH. By in situ hybridization, the plasma cell infiltrate is polytypic for light chains. Histopathologic recognition of CSH is important given several histopathologic mimics and a strong association with hematolymphoid malignancies. Differential diagnoses include neoplasms (GCT, rhabdomyoma), infectious processes (mycobacterial, fungal infections and malakoplakia), storage diseases (e.g., Gauchers) and other histiocytoses. The patient is currently being worked up to rule out an underlying hematologic malignancy or a monoclonal gammopathy.
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