Which of the following is a CRAB feature of multiple myeloma?

• A. Hypercalcemia
• B. M-spike
• C. Anemia
• D. Bone lesions

Answer: (A)

In multiple myeloma, end-organ damage is summarized by the acronym CRAB: hypercalcemia, renal dysfunction, anemia, and bone lesions. Hypercalcemia is a CRAB feature because malignant plasma cells in the bone marrow stimulate osteoclasts and bone resorption, releasing calcium into the bloodstream. This excess calcium can cause symptoms such as fatigue, confusion, dehydration, constipation, and polyuria, signaling that the disease is affecting organs beyond the marrow.

M-spike, or a monoclonal protein spike, is a marker of a plasma cell abnormality but not an end-organ damage finding. It indicates the presence of a clone of abnormal plasma cells, but by itself it does not tell you that organs are being damaged. Anemia and bone lesions are also CRAB features: anemia results from marrow infiltration and suppressed red cell production, while bone lesions reflect osteolytic damage from the malignant plasma cell activity.

So hypercalcemia fits the CRAB pattern because it denotes end-organ involvement, just as anemia and bone lesions do, whereas the M-spike is not part of the CRAB criteria.