Orbital Myeloma and Plasmacytoma: An Australian Study.

PURPOSE The purpose of this study was to provide Australian data on the clinical and radiological features and outcomes in patients with orbital plasmacytomas. METHODS Multicentre retrospective review of orbital plasmacytoma and orbital involvement in multiple myeloma (MM) from 2005 to 2022 in Australia. RESULTS Twenty-one participants were identified. The median age was 62 years (range 34-88 years), and 11 (52%) were females. Eighteen (84%) had a known diagnosis of MM prior to their orbital presentation, with all patients eventually being diagnosed with systemic MM. Thirteen (72%) were receiving active treatment for systemic myeloma on presentation, while 3 (17%) were in remission. All but 1 had unilateral orbital involvement (n = 20, 95%). Common presenting symptoms and signs were decreased visual acuity (n = 13, 62%), proptosis (n = 11, 52%), limited motility (n = 15, 71%), and optic neuropathy (n = 5, 24%). Radiologically, 15 (71%) involved the superotemporal orbit, 7 (33%) inferotemporal orbit, and 16 (76%) involved ≥1 extraocular muscle. Sixteen (76%) were biopsied and confirmed orbital plasmacytoma on histopathology. Treatment modalities included intravenous and oral steroids (n = 7, 33%), chemotherapy (n = 9, 43%), radiotherapy (n = 13, 62%), stem cell transplant (n = 3, 14%), and surgical debulking and decompression (n = 3, 14%). Mortality was high, with 15 (71%) having MM-related mortality. CONCLUSIONS This is the largest cohort of Australian data on orbital plasmacytomas. Most patients have a diagnosis of systemic MM at presentation. It is crucial to recognize and treat these patients early due to a poor systemic prognosis.