High-grade malignant cutaneous plasmacytoma metastatic to the central nervous system. A case report with electron microscopy, immunohistological, and neuropathological studies.

A case of high-grade malignant extramedullary plasmacytoma (EMP), unusual in its initial cutaneous localization and major involvement in the central nervous system rapidly resulting in death, is reported. Light- and electron-microscopic studies of a skin nodule revealed a high proportion of immature and mature plasmacytes. Immunohistological study revealed that both cells synthesized different amounts of a monotypic cytoplasmic kappa light chain. Neuropathological study revealed extensive infiltration of the leptomeninges and perivascular spaces as far as the deep parenchyma. In several places, effraction of vessels resulted in parenchymatous, tumor-like, plasmacytic infiltration. The findings of this case were compared with those of the few previously reported cases of EMP with initial cutaneous or intracranial localization, and with those of immunoblastic sarcoma occurring in some cases of myeloma.