Primary Conjunctival Extramedullary Plasmacytoma: A Case Report and Review of the Literature

A 77-year-old male presented with a painless, raised, erythematous lesion of the left lower eyelid conjunctival fornix, found incidentally on routine ophthalmic examination. Further evaluation demonstrated a mobile, nontender 5 × 4 mm injected mass without scleral or orbital extension. Excisional biopsy revealed dense infiltration of atypical plasmacytoid cells, strongly positive for CD138, MUM1, and CD56, with kappa light chain restriction and a Ki-67 index of 7% to 8%, consistent with a histopathologic diagnosis of plasmacytoma. Markers for melanoma, carcinoma, histiocytic/dendritic tumors, T-cells, and B-cells were not expressed. Systemic workup, including positron emission tomography/CT, serum and urine protein electrophoresis, and bone marrow biopsy, showed no evidence of systemic plasma cell dyscrasia, confirming a diagnosis of primary conjunctival extramedullary plasmacytoma. At 6-month follow-up, the patient remains free of local recurrence without adjuvant therapy. This case contributes to the limited literature on primary conjunctival extramedullary plasmacytoma and highlights the importance of including it in the differential diagnosis of atypical conjunctival lesions.