Sinonasal extramedullary plasmacytoma: A case report of unilateral nasal obstruction with epistaxis.

Sinonasal extramedullary plasmacytoma is a rare localized plasma cell neoplasm arising outside the bone marrow, most commonly involving the upper aerodigestive tract. It typically presents with unilateral nasal obstruction and epistaxis and may mimic a broad spectrum of benign and malignant sinonasal conditions. Cross-sectional imaging usually demonstrates an enhancing soft-tissue mass with possible bone remodeling or destruction; however, imaging findings are not specific, and histopathological confirmation of monoclonal plasma cell proliferation remains essential. A comprehensive systemic evaluation is required to exclude multiple myeloma, which significantly impacts management and prognosis. A 40-year-old patient presented with a 6-month history of progressive unilateral nasal obstruction associated with recurrent epistaxis and visual disturbances. Computed tomography and magnetic resonance imaging revealed an infiltrative sinonasal mass with extension to adjacent structures, including the medial orbital wall. Endoscopic biopsy confirmed extramedullary plasmacytoma with kappa light-chain restriction. Systemic work-up did not reveal evidence of multiple myeloma. The patient was treated with definitive radiotherapy, resulting in favorable clinical evolution with no evidence of recurrence at short-term follow-up. This case highlights the importance of early biopsy of unilateral sinonasal masses and emphasizes the role of imaging in assessing locoregional extension. It also underlines the necessity of systematic evaluation to differentiate isolated extramedullary plasmacytoma from multiple myeloma in order to guide appropriate management.