Intramuscular enhancing masses: Late relapse of multiple myeloma mimicking hematoma in trauma setting

Extramedullary disease (EMD) is an uncommon and aggressive form of multiple myeloma, especially when localized to intramuscular locations. We present a case of a 45-year-old man with a history of IgG multiple myeloma (MM), who underwent allogeneic bone marrow transplantation and had been in clinical remission for more than a decade. He presented acutely after trauma with computed tomography (CT) revealed several enhancing masses in bilateral psoas, right obturator internus, right adductors and left sartorius muscles, which were initially misinterpreted as intramuscular hematomas. These masses remained stable on follow-up imaging, raising concern for underlying undiagnosed soft tissue tumors. Biopsy of one of the masses demonstrated a plasma cell tumor, and further evaluation confirmed relapse of multiple myeloma. Additionally, the largest mass in the left psoas exhibited peripheral calcification-an unusual imaging characteristic of extra ossous myeloma. Despite imaging following trauma, the presence of intramuscular masses in patients with history of MM should raise a high degree of clinical suspicion for EMD. Recognition of this diagnostic pitfall can help avoid delay diagnosis and inappropriate management.