Bilateral proptosis as the initial manifestation of multiple myeloma with orbital involvement: case report and literature review.

Orbital plasmacytoma (OP) is a rare extramedullary manifestation of multiple myeloma (MM), typically presenting unilaterally during the course of previously diagnosed disease. Bilateral OP as the initial manifestation of MM is exceedingly uncommon. We report a 40-year-old woman who presented with rapidly severe bilateral proptosis, visual impairment, and ocular surface damage. Cranio-orbital imaging demonstrated bilateral extraconal masses and diffuse lytic lesions. Immunoelectrophoresis identified monoclonal IgA kappa, and bone marrow aspiration showed 48% dystrophic plasma cells. Histopathological examination of a conjunctival biopsy confirmed extramedullary plasmacytoma, establishing the diagnosis of IgA kappa MM with bilateral OP. Despite a marked early local response after one month of treatment with high-dose corticosteroids and immunochemotherapy, the patient died shortly after. This case highlights an exceptionally rare and aggressive initial presentation of MM with bilateral OP, underscoring the high tumor burden and poor prognosis associated with this unusual manifestation.