Webster's New World Medical Dictionary

melanoma, ocular
A rare type of malignant
melanoma that arises from a structure within the
eye. The most common sites for ocular melanoma
are the choroid, the ciliary body, and the iris. The
tumor may metastasize (spread), most often to the
liver. Ocular melanoma tends to occur after age 40.
melanoma, superficial spreading
One of the
four clinical types of malignant melanoma, the most
common type in white people, which typically pres-
ents as a raised, irregular, colored area that starts in
a mole-like shape and spreads across the skin.
melanosis coli
A benign, reversible condition
that is usually, but not always, associated with long-
term use of laxatives in which pigment deposition in
the lamina propria of the large intestine results in a
brown to black discoloration of the mucosa (lining)
of the large intestine. Melanosis coli is sometimes
called pseudomelanosis coli because the pigment
deposited is lipofuscin and not melanin, as the
name implies. Melanosis coli produces no
symptoms.
MELAS syndrome
Mitochondrial encephalopa-
thy, lactic acidosis, and stroke-like episodes syn-
drome, a rare form of dementia caused by
mutations in the genetic material (DNA) in the mito-
chondria. Most DNA is in the chromosomes in the
cell nucleus, but another important cell structure
that carries DNA is the mitochondrion. Much of the
DNA in the mitochondrion is used to manufacture
proteins that help to produce energy. As a result of
265
MELAS syndrome
14_189283 ch13.qxp 4/18/08 10:17 PM Page 265
http://www.rashidislamiccenter.com
http://www.allofislam.com/

---

the disturbed function of their cells’ mitochondria,
patients with MELAS syndrome develop brain dys-
function (encephalopathy), with seizures and
headaches, as well as muscle disease, with a
buildup of lactic acid in the blood (lactic acidosis),
temporary local paralysis (stroke-like episodes),
and abnormal thinking (dementia). MELAS syn-
drome is diagnosed via muscle biopsy that shows
characteristic ragged red fibers. Brain biopsy shows
stroke-like changes. MELAS syndrome can affect
people at different times of life, but most patients
show symptoms before age 20. Patients are treated
according to which areas of the body are affected at
a particular time. There is no known cure for
MELAS, which is progressive and fatal.
melasma
Pigmentation of the cheeks of the face
(malar area). When it occurs during pregnancy it is
referred to as chloasma or the mask of pregnancy.
Melasma darkens with sun exposure. 
melatonin
A hormone that is produced by the
pineal gland and is intimately involved in regulating
the sleeping and waking cycles, among other
processes. Some people who have chronic insomnia
use melatonin supplements. However, melatonin is
not recommended for all patients with sleep prob-
lems, so one should consult a physician before tak-
ing it.