Atypical Monoclonal Plasma Cell Hyperplasia of the Central Nervous System: Precursor of Plasmacytoma with Evolutionary Considerations

Hematopoietic proliferations rich in plasma cells rarely occur within the central nervous system without the involvement of other organ systems. Depending on their histological pattern and cellular composition, several different terms, including plasmacytoma, plasma cell granuloma, hyalinizing plasmacytic granulomatosis, and inflammatory meningioma, are used for these lesions. We report a left temporal dural lesion composed of plasma cells, lymphocytes, histiocytes, and rare eosinophils with hyaline changes and a suggestion of follicle formation, which stained predominantly for IgG and kappa light chains. This lesion arose in an otherwise healthy 52-year-old woman. Free kappa light chains without a monoclonal peak were found in the urine. We are aware of only two other heterogeneous, predominantly plasmacytic, solitary dural lesions that were found to be monoclonal on immunohistochemical examination. The label atypical monoclonal plasma cell hyperplasia appears to suit the morphological characteristics of our lesion. We suggest that a spectrum of solitary plasmacytic lesions may occur within the central nervous system and that atypical plasma cell hyperplasias have the potential to evolve into plasmacytoma. The preneoplastic nature of this lesion and its potential for evolution to malignant myeloma should be considered when planning treatment and lifelong follow-up for patients.