Rationale: Plasma cell neoplasms are categorized by neoplastic proliferation of a single clone of plasma cells which produce a monoclonal immunoglobulin. Plasma cell neoplasms can present as a solitary plasmacytoma or as multiple myeloma. Both of them can progress to multiple myeloma. Once a diagnosis of plasmacytoma has been made, thorough examinations should be carried out for identifying the disease entity.
Patient concerns and diagnoses: Herein, we describe an extraordinary rare case of multiple myeloma with initial presentation of a left sphenoid neoplasm resulting in left-sided headache and rapid deterioration of visual acuity. Histo-pathologic analysis revealed a plasma cell neoplasm with positive immunostaining for cluster of differentiation (CD)138, CD79a, and kappa light chain of immunoglobulin. A bone marrow aspiration was then performed, and the diagnosis of multiple myeloma was then confirmed.
Interventions and outcomes: After investigative workup, our patient received chemotherapy, localized radiotherapy, and autologous stem cell transplantation. Her visual acuity recovered to the baseline and she sustained a partial response without subjective discomfort.
Lessons: Extramedullary plasmacytoma is an interesting but infrequent presentation of multiple myeloma. Moreover, involvement of the sphenoid sinus in multiple myeloma resulting in extrinsic optic nerve compression is extremely rare. Clinicians should consider plasmacytoma as a diagnostic possibility when presented with cases of solitary sphenoid neoplasm and rapid progression of clinical course.