Crystal-storing histiocytosis associated with a lymphoplasmacytic neoplasm mimicking adult rhabdomyoma: a case report and review of the literature.

Massive accumulation of crystals within histiocytes in association with a lymphoplasmacytic neoplasm causing histologic features closely mimicking adult rhabdomyoma is a rare occurrence. We report the case of a 49-year-old man who presented with a left posterior cervical mass. Histologic examination demonstrated sheets of large, elongated, and polygonal cells with prominent eosinophilic cytoplasm surrounding scattered dense lymphoplasmacytic collections. Evidence of the reactive histiocytic nature of the eosinophilic cells was provided by an immunohistochemical reaction that was positive with KP-1 (CD68), but negative with common muscle actin, desmin, and myoglobin. The ultrastructural finding of elongated and rhomboid, membrane-bound, cytoplasmic crystals further supported the reactive histiocytic nature of these cells. B-cell kappa monoclonality of the lymphoplasmacytic component was proven by gene rearrangement studies. A recurrence involving the right parotid gland, 18 months after removal of the cervical mass, confirmed the aggressive nature of this B-cell lymphoma. Misdiagnosis of crystal-storing histiocytosis as adult rhabdomyoma can be avoided if the following features are recognized: lack of cytoplasmic cross striations, frequent multinucleation of the histiocytes, and prominence of the atypical lymphoplasmacytic component.