Crystal-storing histiocytosis associated with lymphoplasmacytic neoplasms. Report of three cases mimicking adult rhabdomyoma.

Massive crystal deposition is rare in lymphoplasmacytic (LPc) or plasma cell neoplasms. We report three cases in which the accumulation of crystals in histiocytes closely reproduced the histologic features of adult rhabdomyoma. The patients, all female, aged 18, 77, and 78 years, presented with tumor of cervical lymph nodes (two cases) or the otolaryngic mucosa (two cases). In addition, two patients had monoclonal serum or urine immunoglobulin (IgM-kappa-1, unknown-1), and one had renal and bone marrow involvement on biopsy. This last patient died of acute renal failure at 5 months, another was alive without disease at 8 years, and the remaining one was lost to follow-up. Lymph nodes, mucosae, and kidney showed a neoplastic LPc infiltrate masked by sheets of large benign histiocytes containing sheaves of crystals. Paraffin-section immunohistochemistry demonstrated monoclonal staining of the LPc cells in all cases (IgM-kappa-2, IgA-kappa-1) and of the crystals (IgM-kappa) in one case. In all patients, the crystal-containing cells were positive for KP-1 (CD68), but not for desmin, muscle-specific actin, or myoglobin. These findings suggest that, in any case of adult rhabdomyoma in which the histologic findings are not typical, a crystal-storing histiocytosis should be ruled out: recognition of the atypical LPc component and the histiocytic immunophenotype of the crystal-storing cells will help prevent a serious misdiagnosis.