[Unusual presentation of plasma cell myeloma]

A 41 year-old woman consulted because of facial pain. A magnetic resonance imaging showed a mass in the right petrous apex. A biopsy revealed a diffuse proliferation of large atypical cells with plasmablastic appearance, positive for CD138, BCL6, CD56 and p53. The proliferation factor was 80%. Monoclonal kappa light chain expression was observed. Because the unusual clinicopathological features the patient was studied to rule out systemic plasma cell myeloma. Bone scan disclosed multiple cranium osteolytic lesions; proteinogram showed hypogammaglobulinemia and immunofixation in serum and urine were negative. Afterwards, bone marrow biopsy was performed and it presented a 30% infiltration of the bone cylinder by mature plasma cells. These were monoclonal for kappa light chain with focal expression of p53 and without expression of CD56. These findings suggested the diagnosis of multiple myeloma. This case proposes a morphological spectrum of plasma cell neoplasms, showing a continuous clonal evolution of tumor cells, with an acquired plasticity of dedifferentiate, become immature and infiltrate extramedullary tissues, a fact possibly determined by accumulation of multiple genetic alterations. These findings confirm the difficulty of the differential diagnosis from histopathology study between plasmablastic lymphoma and plasmablastic transformation of plasma cell myeloma because of the nearly identical immunohistochemical profiles.