(Greek: bone marrow; the spinal cord and medulla oblongata; the myelin sheath of nerve fibers)
2. A cancer that begins in plasma cells.
Plasma cells are white blood cells which make antibodies. Antibodies are part of the immune system. They work with other parts of the immune system to help protect the body from germs and other harmful substances. Each type of plasma cell makes a different antibody.
Myeloma, like other cancers, begins in cells. Normally, cells grow and divide to form new cells as the body needs them.
When cells grow old, they die, and new cells take their place. In cancer, this orderly process goes wrong. New cells form when the body does not need them, and old cells do not die when they should. These extra cells can form a mass of tissue called a growth or tumor.
Myeloma begins when a plasma cell becomes abnormal and that abnormal cell divides to make copies of itself. The new cells divide again and again, making more and more abnormal cells. The abnormal plasma cells are myeloma cells.
In time, myeloma cells collect in the bone marrow where they may crowd out normal blood cells. Myeloma cells also collect in the solid part of the bone.
The disease is called multiple myeloma because it affects many bones. If myeloma cells collect in only one bone, the single mass is called a plasmacytoma or cancer of the plasma cells (white blood cells that produce antibodies).
As myeloma cells increase in number, they damage and weaken the bones, causing pain and often fractures. When bones are damaged, too much calcium is released into the blood, leading to loss of appetite, nausea, thirst, fatigue, muscle weakness, restlessness, and confusion.
Chemotherapy and bone marrow transplant are currently the primary treatments.
2. An abnormality in development of the spinal cord; especially, the lower part of the cord.
The arachnoid is named for its delicate, spider-web-like filaments that extend from its under surface through the cerebrospinal fluid in the subarachnoid space to the pia mater or the innermost membrane surrounding the central nervous system.