Webster's New World Medical Dictionary

mycoplasma pneumoniae
A mycoplasma that
can infect the upper respiratory tract and the lungs.
Mycoplasma pneumoniae is a major cause of respi-
ratory infection in children of school age and young
adults. It is also a common cause of pneumonia in
persons with HIV. Treatment involves use of antibi-
otics, including tetracycline and erythromycin.
mycosis fungoides
A type of non-Hodgkin’s
lymphoma that first appears on the skin. Also
known as cutaneous T-cell lymphoma.
mydriasis
Dilation of the pupil. The opposite of
mydriasis is miosis.
myelin
The fatty substance that covers and pro-
tects nerves. Myelin is a layered tissue that sur-
rounds the nerve fibers (axons). This sheath
around the axons acts like a conduit in an electrical
system, ensuring that messages sent by axons are
not lost en route.
myelination
The formation of the myelin sheath
around a nerve fiber. Also known as myelinization.
See also 
myelin.
myelitis
Inflammation of the spinal cord, such as
from infection or immune inflammation.
myelodysplastic syndrome
One of a group of
disorders characterized by abnormal development
of one or more of the cell lines that are normally
found in the bone marrow. Patients can develop a
variety of symptoms related to anemia, low or high
white blood cell count, infections, and bleeding
problems. Myelodysplastic syndrome may progress
and become acute leukemia. The well-recognized
myelodysplastic syndromes include refractory ane-
mia, refractory anemia with ringed sideroblasts,
refractory anemia with excess blasts, refractory ane-
mia with excess blasts in transformation, chronic
myelomonocytic leukemia, chronic myelomono-
cytic leukemia in transformation, and unclassified
myelodysplastic syndrome. Also known as
preleukemia or smoldering leukemia.