Multiple myeloma.

Multiple myeloma is characterized by abnormalities in plasma cells, a type of white blood cell. These abnormal cells multiply out of control, increasing from about one percent of cells in the bone marrow to the majority of bone marrow cells. The abnormal cells form tumors within the bone, causing bone pain and an increased risk of fractures. If the tumors interfere with nerves near the bones, numbness or weakness in the arms or legs can occur. Affected individuals may also experience a loss of bone tissue, particularly in the skull, spine, ribs, and pelvis. The deterioration of bone can result in an excess of calcium in the blood (hypercalcemia), which can lead to nausea and loss of appetite, excessive thirst, fatigue, muscle weakness, and confusion.