Webster's New World Medical Dictionary

wormwood
The plant whose essence forms the
basis of absinthe, a dangerous emerald-green
liqueur. See also 
absinthe.
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wormwood
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WPW syndrome
Wolff-Parkinson-White syn-
drome.
wrist
The part of the hand that is nearest the fore-
arm and consists of the carpal bones and the asso-
ciated soft tissues. The eight carpal bones are
arranged in two rows. One row of carpal bones
joins the long bones of the forearm (the radius,
and, indirectly, the ulna). Another row of carpal
bones meets the hand at the five metacarpal bones
that make up the palm.
writer’s cramp
See 
cramp, writer’s.
wryneck
See 
torticollis, congenital.
WS
Waardenburg syndrome.
Wt
Abbreviation for weight. For example, “Wt 80
lbs” means “weight 80 pounds.”
WPW syndrome
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X
In genetics and medicine, X chromosome.
X chromosome
The sex chromosome that is
found twice in normal females and singly, along with
a Y chromosome, in normal males. The complete
chromosome complement consists of 46 chromo-
somes, including the 2 sex chromosomes, and is
thus conventionally written as 46,XX for chromoso-
mally normal females and 46,XY for chromosomally
normal males.
xanthelasma
Tiny, slightly raised, yellowish
plaques on the skin surface of the upper or lower
eyelids. Xanthelasma is a harmless growth of tissue
caused by tiny deposits of fat in the skin, and it is
often associated with abnormal blood fat levels
(hyperlipidemia). Xanthelasma is composed of
lipid-laden foam cells called histiocytes. Treatment
is directed toward any underlying lipid disorder
when present. Dermatologists can remove the
abnormal plaques. See also 
xanthoma.
xanthinuria
A rare metabolic disorder that is
caused by lack of an enzyme needed to process xan-
thine, an alkaloid found in caffeine; theobromine;
theophylline; and related substances. Unchecked,
xanthinuria can lead to kidney stone formation.
Treatment involves avoiding foods and drinks that
contain xanthine derivatives, such as coffee, tea, and
cola. Classic xanthinuria is inherited in an autoso-
mal recessive manner and involves a defect in the
enzyme xanthine dehydrogenase.
xanthoma
A firm yellow, orange, or brown nod-
ule deep in the skin (such as around the Achilles
tendon, elbows, or knees) or mucous membrane
caused by fat deposition. Although xanthomas them-
selves are harmless, they frequently indicate under-
lying disease, such as diabetes, lipid disorders
(such as elevated blood cholesterol levels), or other
conditions. They are composed of lipid-laden foam
cells called histiocytes. Treatment is directed toward
any underlying disorder when present. The nodules
can be resected surgically for cosmetic purposes.
Xanthoma is distinguished from xanthelasma by
being a large nodule deep in the tissues as opposed
to a plaque on the skin surface, but both can occur
from lipid disorders. See also 
xanthelasma.