Fulminant extramedullary relapse of multiple myeloma with rare cardiac, vascular, and multivisceral involvement: A case report.

Multiple myeloma (MM) is a plasma cell malignancy that typically follows a protracted clinical course. Extramedullary disease (EMD) represents an aggressive manifestation of MM with a relatively low incidence, traditionally involving the skin and soft tissues. While MM usually progresses indolently, fulminant disease progression characterized by extensive multivisceral and vascular infiltration is exceptionally rare and seldom documented in the medical literature. This case illustrates a 64-year-old woman who presented with left chest wall mass and pain and was diagnosed with high-risk IgG-λ-type MM (R-ISS Stage II), harboring 1q21 amplification and IGH/FGFR3 translocation. Following 12 cycles of VCD (bortezomib, cyclophosphamide, and dexamethasone) induction, she achieved partial remission and proceeded to maintenance therapy with bortezomib and ixazomib. Fifteen months post-diagnosis, the patient presented with a rapidly enlarging abdominal wall mass. 18F-FDG PET-CT revealed widespread hypermetabolic activity involving the heart, major blood vessels, liver, spleen, lungs, and multiple soft tissue sites, indicating extensive EMD. Bone marrow examination showed only 1% plasma cells, demonstrating a marked dissociation between systemic EMD and medullary involvement. Despite salvage therapy with carfilzomib, liposomal doxorubicin, and dexamethasone, the patient's condition deteriorated rapidly. Compounded by severe hypoproteinemia, electrolyte disturbances, and respiratory infection, the disease followed a fulminant course, ultimately leading to the patient's death. This case represents a catastrophic transition of genetically high-risk MM from initial medullary involvement to widespread multivisceral and cardiovascular infiltration upon relapse. It highlights a rare phenotype of relapsed/refractory MM where aggressive extramedullary proliferation occurs independently of bone marrow progression. Such patients face a dismal prognosis and present a formidable challenge for current salvage therapeutic strategies.