Webster's New World Medical Dictionary

multiple myeloma
A bone marrow cancer that
involves a type of white blood cell called a plasma (or
myeloma) cell. The tumor cells in myeloma can form
a single collection (plasmacytoma) or many tumors
(multiple myeloma). Plasma cells are normally part
of the immune system; they make antibodies.
Because myeloma patients have an excess of identical
plasma cells, they have too much of one type of anti-
body. 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. Myeloma cells prevent
the bone marrow from forming normal plasma cells
and other white blood cells that are important to the
immune system, so patients with multiple myeloma
may not be able to fight infections. Myeloma cells can
also prevent the growth of new red blood cells in the
marrow, causing anemia. Excess antibody proteins
and calcium may prevent the kidneys from filtering
and cleaning the blood properly. Chemotherapy and
bone marrow transplant are the primary treatments.
Also known as plasma cell myeloma and myeloma.
multiple personality disorder
See 
dissocia-
tive disorder.
multiple sclerosis
A disease that is characterized
by loss of myelin (demyelinization). Abbreviated MS.
Myelin, the coating of nerve fibers, is composed of
lipids (fats) and protein. It serves as insulation and
permits efficient nerve fiber conduction. In MS,
demyelinization usually affects white matter in the
brain, but sometimes it extends into the gray matter.
When myelin is damaged, nerve fiber conduction is
faulty or absent, and nerve cell death may occur.
Impaired bodily functions or altered sensations
associated with those demyelinated nerve fibers give
rise to the symptoms of MS, which range from