Felon Mahrous

Introduction

A plasmacytoma is a localized tumour composed of monoclonal plasma cells, which are antibody-producing cells derived from B lymphocytes (1). It represents a focal form of plasma cell dyscrasia and occurs either as a solitary bone plasmacytoma or as an extramedullary plasmacytoma arising in soft tissues (2). Extramedullary plasma tumours are rare and account for roughly 3–5 % of all plasma cell neoplasms (3). Unlike multiple myeloma, plasmacytoma lacks diffuse bone marrow involvement and systemic features, although it carries a risk of progression to multiple myeloma over time (4). It often presents diagnostic challenges due to its varied and site-specific clinical manifestations.

Proptosis is a common ophthalmic sign associated with a wide spectrum of orbital and craniofacial pathologies, including inflammatory, neoplastic, and vascular conditions. However, plasma cell neoplasms rarely involve the orbit or adjacent cranial bones, with Orbital plasmacytoma representing approximately <1% of all orbital tumours in published series (5). Solitary plasmacytomas account for a small proportion of plasma cell dyscrasias, with temporal bone involvement being particularly uncommon (6). We report a case of a temporal bone plasmacytoma presenting primarily with ophthalmic signs, emphasizing the importance of considering systemic malignancies in the differential diagnoses of proptosis.

Case Report

A 68-year-old female was referred to the ophthalmology clinic after presenting to a maxillofacial clinic with a three-month history of progressive left-sided proptosis and a painless swelling over the left temporal region. The patient described a pulsatile sensation over the mass but denied visual loss, diplopia, ocular pain, or systemic symptoms such as weight loss or fatigue. Although the patient felt well in herself, her family felt like there were some behavioral and memory changes that had developed as the plasmocytoma progressed.

Ophthalmic examination revealed non-axial left proptosis with mild restriction of extraocular motility in lateral gaze. Visual acuity, pupillary responses, intraocular pressure, and fundoscopic examination were within normal limits. External examination demonstrated a firm, non-tender, pulsatile mass over the left temporal region.

Computed tomography of the orbit and skull showed a lytic lesion of the left temporal bone with cortical destruction and extension into the orbit and temporal lobe. Magnetic resonance imaging revealed an enhancing intraosseous and extraosseous mass causing mass effect on the globe without optic nerve compression. There was no evidence of flow voids to suggest the presence of a vascular lesion.

An incisional biopsy of the temporal mass was performed and histopathology revealed sheets of atypical plasma cells with eccentric nuclei and prominent nucleoli. Immunohistochemical staining was positive for CD138 and demonstrated monoclonal light chain restriction, consistent with plasmacytoma.

Systemic evaluation, including bone marrow biopsy, serum protein electrophoresis, immunofixation, serum free light chain analysis, and skeletal survey, showed no evidence of multiple myeloma hence a diagnosis of a solitary temporal bone plasmacytoma was established. Given its intracranial extension, the nearest neurosurgical unit was consulted to guide further management and explore neurosurgical necessity.

The patient underwent definitive localised radiotherapy. At three-month follow-up, there was marked reduction in the size of the temporal mass and improvement of proptosis, with preserved visual function. She remains under long-term surveillance.

Discussion points

Orbital involvement in plasma cell neoplasms is rare and often represents secondary spread from adjacent structures such as the paranasal sinuses or skull base. Temporal bone plasmacytomas may present with otologic symptoms; however, ophthalmic manifestations such as proptosis are infrequently reported.

Pulsatility of a craniofacial mass may raise suspicion for vascular lesions including arteriovenous malformations or aneurysms. In this case, absence of flow voids on imaging and histological confirmation were crucial in establishing the diagnosis.

From an ophthalmologic perspective, early recognition of atypical causes of proptosis is essential to prevent visual morbidity. Radiotherapy remains the mainstay of treatment for solitary plasmacytoma and is associated with good local control. Long-term follow-up is mandatory due to the risk of progression to multiple myeloma.

Conclusion

Temporal bone plasmacytoma is a rare cause of proptosis and may mimic more common orbital or vascular conditions. Ophthalmologists should maintain a high index of suspicion for plasma cell neoplasms in patients with destructive cranio-orbital lesions. Prompt diagnosis and multidisciplinary management can result in favourable visual and systemic outcomes.

References

1. Iqbal QUA, Majid HJ. Plasmacytoma [Internet]. PubMed. Treasure Island (FL): StatPearls Publishing; 2022. Available from: https://www.ncbi.nlm.nih.gov/books/NBK573076/
2. Uğur Hatipoğlu, Mert Seyhan, Turgay Ulas, Dal MS, Fevzi Altuntaş. Solitary Plasmacytomas: Current Status in 2025. Hematology Reports [Internet]. 2025 Jun 30 [cited 2025 Sep 5];17(4):32. Available from: https://www.mdpi.com/2038-8330/17/4/32
3. Ge S, Zhu G, Yi Y. Extramedullary plasmacytoma of the larynx: Literature review and report of a case who subsequently developed acute myeloid leukemia. Oncology Letters. 2018 Jun 19.
4. Soutar R, Lucraft H, Jackson G, Reece A, Bird J, Low E, et al. Guidelines on the diagnosis and management of solitary plasmacytoma of bone and solitary extramedullary plasmacytoma. Clin Oncol (R Coll Radiol). 2004 Sep 1;16(6):405–13.
5. Andreia Margarida de Matos, André Goulard, André Ribeiro, Ricardo Freitas, Catarina Monteiro, Paulo Martins. Orbital Plasmacytoma, An Uncommon Presentation of Advanced Multiple Myeloma. European Journal of Case Reports in Internal Medicine [Internet]. 2020 Jan 31;7(3). Available from: https://pmc.ncbi.nlm.nih.gov/articles/PMC7083190/
6. Wein RO, Popat SR, Doerr TD, Dutcher PO. Plasma Cell Tumors of the Skull Base: Four Case Reports and Literature Review. Skull Base. 2002;12(2):077–86.