Extramedullary plasmacytoma of the orbit complicating the evolution of multiple myeloma in complete remission

Orbital plasmacytoma is rare and has only been reported in the context of the initial diagnosis of multiple myeloma. Moreover, isolated orbital plasmacytoma without any signs of multiple myeloma is extremely rare. We report the case of a 59-year-old female patient diagnosed with IgA Kappa multiple myeloma. It was stage I ISS (International Staging System) and stage I R-ISS (Revised ISS). According to the Tunisian national protocol, the patient was included in the standard-risk group and was eligible for four cycles of CTD (Cyclophosphamide, Thalidomide, Dexamethasone) followed by autologous stem cell transplantation. Taking into account the partial response after the CTD cycles, the patient has benefited from two VTD cycles (Bortezomib, Thalidomide, Dexamethasone). Thus, complete remission was obtained. The patient refused autologous stem cell transplantation. Therefore, maintenance treatment based on Thalidomide only was started and received over a twelve-month period. Five months after the end of maintenance treatment, she reported frontal headaches that were resistant to symptomatic treatment, with ptosis in the right eye in physical examination. Brain MRI revealed the presence of a right cranio-orbital tissue mass with intra-orbital and extra-axial cerebral components. The mass measured 32/36 mm on axial sections and 47 mm in height. The patient underwent a complete resection of the cranio-orbital mass with cranioplasty. The histopathological examination of the mass with Immunohistochemistry staining confirmed the diagnosis of orbital plasmocytoma. An update of the multiple myeloma assessment did not reveal any biological, cytological or radiological signs in favor of multiple myeloma. Therefore the diagnosis of isolated orbital plasmacytoma without signs of multiple myeloma was made. Post-operative brain MRI showed complete disappearance of the right cranio-orbital tissue lesion. There was only a persistent meningeal enhancement of the dura mater at the surgical site, suggestive of post-operative changes. The patient was then referred for cranio-orbital radiotherapy.