Sphenoid plasmacytoma as initial presentation of multiple myeloma-case report.

Plasmacytoma is a rare plasma cell neoplasm. Whether solitary or associated with multiple myeloma (MM), it rarely involves the skull base, particularly the sphenoid bone. We present a unique case of sphenoid bone plasmacytoma secondary to MM, highlighting diagnostic and therapeutic challenges. A 56-year-old female presented with headaches, vomiting, epistaxis, and cranial nerve deficits. Cerebral imaging revealed a 65-mm tumor infiltrating the sphenoid bone and adjacent structures. Subtotal resection was performed using an endoscopic nasal approach. Histopathology revealed plasmacytoma, and diagnostic workup confirmed MM. By the end of biological exploration, relapse of the sphenoid plasmacytoma was observed, and the patient was successfully treated with radiotherapy, immunochemotherapy, and autologous stem cell transplantation. After 18-month follow-up, sustained complete remission was confirmed. Although rare, the diagnosis of plasmacytoma should be considered in cases of skull base tumors. This localization is highly predictive of MM, warranting comprehensive investigations to initiate prompt and adequate management.