Supplementary Material for: Sequential Myelomatous Pleural and Pericardial Effusions in Multiple Myeloma: A Case Report Demonstrating Extended Survival with Teclistamab

Abstract
Background: Myelomatous pleural effusion (MPE) and pericardial involvement are rare manifestations of multiple myeloma, occurring in less than 1% of cases and carrying historically poor prognoses. We present a unique case where both these rare serous cavity manifestations occurred sequentially in the same patient, demonstrating the evolving treatment landscape with novel targeted therapies.
Case Presentation: A 42-year-old Asian female presented with left shoulder pain and swelling, leading to the diagnosis of IgG Lambda Multiple Myeloma with extensive extramedullary disease. After initial partial response to D-VRD therapy, she developed MPE with complete left lung collapse. Following failure of second-line KPD-PACE therapy, she received Teclistamab, achieving complete metabolic and morphological response documented by PET-CT. After maintaining remission for 10 months, she experienced relapse with pericardial involvement presenting as cardiac tamponade.
Results: The patient demonstrated an unprecedented response to BCMA-targeted therapy with Teclistamab, achieving complete remission that lasted 10 months - more than doubling the historical median survival of 4 months for MPE. Flow cytometry proved instrumental in rapid diagnosis, showing 11% lambda monotypic plasma cells in the pleural fluid. The subsequent pericardial involvement after initial complete response highlighted the persistent challenges in managing extramedullary disease.
Conclusion: This case represents the first documented instance of sequential MPE and pericardial involvement in multiple myeloma, demonstrating the potential of novel targeted therapies, particularly BCMA-directed approaches, in extending survival and improving outcomes in these rare but aggressive disease manifestations.
Keywords: Multiple myeloma, myelomatous pleural effusion, pericardial effusion, extramedullary disease, Teclistamab