Clival plasmacytoma: an exceedingly unusual extramedullary relapse of multiple myeloma
Materials and Methods/Case Presentation/Objective:
A 60-year-old-male patient diagnosed with immunoglobulin G (IgG) kappa MM [t(11;14)] in 2016 received lenalidomide/bortezomib/dexamethasone (RVD), daratumumab/bortezomib/dexamethasone, and autologous stem cell transplant (ASCT) (2017), followed by bortezomib maintenance until biochemical progression (2018). Subsequent lines included daratumumab/carfilzomib/dexamethasone (2019-2021) and elotuzumab/pomalidomide/dexamethasone (2021-2023), after which he was lost to follow-up for two years.
In July 2025, he presented after occupational head trauma and CT incidentally revealed a 3.3 x 3.1 cm sellar lesion. The patient then developed blurry vision, and magnetic resonance imaging (MRI) demonstrated a 3.6 x 3.6 x 3.5 cm destructive clival lesion. Monoclonal protein (M-protein) was 7.7 g/dL, and bone marrow showed 70-80% plasma cells. Biopsy confirmed clival plasmacytoma. A multimodal therapy strategy was initiated: cyclophosphamide for cytoreduction, palliative radiation (2,000 cGy/10 fractions) to the clival mass, teclistamab (complicated by grade 1 cytokine release syndrome [CRS]) followed by talquetamab (switched to preserve B-cell maturation antigen [BCMA]-directed chimeric antigen receptor T-cell [CAR-T] eligibility), daratumumab/selinexor (without response), and bortezomib/dexamethasone/cisplatin/doxorubicin/cyclophosphamide/etoposide (VD-PACE). MRI in February 2026 demonstrated a significant reduction in the clival mass, to 2.3 x 1.8 x 1.8 cm. Following VD-PACE, marrow plasma cells decreased to 30% and M-protein declined to 3.3 g/dL. The patient then proceeded with CAR-T and received ciltacabtagene autoleucel. By day +77 post-CAR-T, PET-CT showed no avid myelomatous lesions, and M-protein declined to 0.5 g/dL- a 94% reduction from relapse.
Results/Description/Main Outcome Measure(s): This case highlights that the superior clivus is a surveillance blind spot in MM- standard PET-CT fields do not capture this region, and disease was detected coincidentally in this case. Clinicians should suspect cerebral extramedullary disease when MM patients present with visual changes or sellar abnormalities. Also, a dedicated skull base MRI confirmed a local clival response before CAR-T; however, no post-CAR-T skull base imaging was obtained, underscoring the need for site-specific imaging in cranial base extramedullary MM. It's also worth noting that sequential BiTE therapy usage- teclistamab (BCMA-directed) followed by talquetamab (GPRC5D-directed) - maintained disease control while preserving BCMA-directed CAR-T eligibility, a strategy used for refractory disease but not previously documented in the context of skull base extramedullary relapse.
Conclusion(s).: This case demonstrates that MM can present at the superior clivus, an evasive site that warrants dedicated imaging if clinical suspicion is high. The decision to use a bridging strategy with sequential BiTE therapy to CAR-T therapy provided a robust systemic response in this heavily refractory and unusually relapsed patient.
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