What are typical sites of involvement in multiple myeloma?

• A. Brain and spinal cord.
• B. Lymph nodes in neck and armpits.
• C. Bone marrow of spine, pelvis, ribs, and skull.
• D. Skin and soft tissue.

Answer: (C)

In multiple myeloma, malignant plasma cells grow primarily in the bone marrow. Because the marrow is most abundant in certain bones, the disease most commonly involves the bone marrow of the spine, pelvis, ribs, and skull. This marrow involvement explains symptoms like bone pain and anemia and leads to characteristic bone lesions seen on imaging.

Other sites listed are not typical primary locations for myeloma cells: the brain and spinal cord are central nervous system structures, not marrow; lymph nodes are more characteristic of lymphomas; skin involvement is rare for myeloma. So the most accurate description of typical involvement is the bone marrow of the spine, pelvis, ribs, and skull.