Rare Extramedullary Manifestations of Multiple Myeloma: A Case Series Involving the Thyroid, Pleura, and Skin

Multiple myeloma is a malignancy characterized by the monoclonal proliferation of plasma cells, primarily within the bone marrow. While it predominantly remains confined to the marrow, extramedullary plasmacytomas, though rare, can occur in various anatomical sites. This report presents three cases of extramedullary plasmacytomas in uncommon locations (the thyroid, pleura, and skin) in patients with an established diagnosis of multiple myeloma. Each case was diagnosed using histopathological examination and immunohistochemical profiling. The thyroid plasmacytoma was identified through thyroid lobectomy, while pleural and cutaneous involvements were detected via biopsy of a pleural and a subcutaneous mass, respectively. These cases highlight the diversity of extramedullary plasmacytoma manifestations and underscore the importance of considering multiple myeloma in the differential diagnosis when atypical extramedullary tumors are identified.