A rare presentation of extramedullary multiple myeloma as a large gluteal soft tissue mass: A case report

Extramedullary multiple myeloma is a rare condition, occurring in 7 % to 18 % of cases, where malignant plasma cells spread beyond the bone marrow to various organs and soft tissues. This report presents a case of secondary extramedullary multiple myeloma with an unusual soft tissue mass, highlighting diagnostic challenges, management considerations, and the importance of early detection.

A 78-year-old woman with a history of multiple myeloma and AL amyloidosis presented with a rapidly enlarging, non-tender gluteal mass over the past two months. Physical examination disclosed a firm, non-tender mass palpable in the left buttock, measuring approximately 23 cm. Imaging revealed osteolytic lesions in the left hip and a large mass invading surrounding tissues. A surgical biopsy was performed. Histological examination revealed a highly cellular malignant proliferation composed of atypical plasma cells arranged in sheets, surrounded by a thick fibrous capsule. Immunohistochemistry showed strong CD138 positivity, confirming the diagnosis of extramedullary plasmacytoma. The patient was scheduled for adjuvant radiotherapy but passed away due to severe pneumonia shortly after the first session of treatment.

The case underscores the diagnostic challenges and importance of a comprehensive evaluation in extramedullary multiple myeloma. Early detection and appropriate management are crucial for optimal patient care.

This case highlights the significance of recognizing and managing extramedullary multiple myeloma, particularly in patients with uncommon soft tissue presentations. Comprehensive evaluation and timely intervention are essential for enhancing patient outcomes in such cases.