Webster's New World Medical Dictionary

pseudoxanthoma elasticum
A disorder that is
characterized by deposition of calcium and other
minerals in elastic fibers. It can affect elastic fibers
prothrombin
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in the skin, eyes, and blood vessels, and less fre-
quently other areas. Abbreviated PXE. PXE is inher-
ited in an autosomal recessive manner and is due to
mutations in the ABCC6 gene on chromosome 16.
Symptoms include small yellow-white raised areas
in the skin folds on the neck, armpits, and other
areas. A physician may see abnormalities in the
back of the eye called angioid streaks, tiny breaks in
the elastin-filled tissue that can lead to blindness.
Impairment of blood vessels in the legs can lead to
pains in the legs while walking (claudication).
psilocybin
An hallucinogenic compound
obtained from certain mushrooms.
psittacosis
An infectious disease that is due to a
bacterium (Chlamydia psittaci) contracted from
psittacine birds, especially caged birds such as par-
rots, parakeets, and lovebirds. It is also seen in
turkey-processing plants. C. psittaci enters the
human body by inhalation of air containing dried
secretions from infected birds. Signs and symptoms
include fever and chills, ill feeling (malaise), loss of
appetite, cough, and shortness of breath. Diagnosis
is made by finding the bacterium in the patient’s
blood or sputum. Treatment involves use of antibi-
otics, such as tetracycline. To avoid psittacosis, one
should avoid dust from bird feathers and cage
contents and not handle sick birds. Also known as
parrot fever.
psoas
Two muscles of the lower back. There are
two psoas muscles on each side of the back. The
larger of the two is called the psoas major and the
smaller the psoas minor. The psoas major originates
at the spine, around the bottom of the rib cage, and
runs down to the thighbone (the femur). The psoas
major acts to flex the hip. The psoas minor also
originates at the spine, around the bottom of the rib
cage, but it runs down to the bony pelvis. The psoas
minor acts to flex the lower (lumbar) spine.
psoriasis
A reddish, scaly, plaque-like rash that is
often located over the surfaces of the elbows, knees,
and scalp, and around or in the ears, navel, genitals,
or buttocks. Approximately 10 to 15 percent of
patients with psoriasis develop joint inflammation
(inflammatory arthritis). Psoriasis is caused by the
body making too many skin cells as the result of an
immune system disturbance in which the body’s T
lymphocytes attack healthy skin cells. Treatment
options include use of topical steroid creams, use of
tar soap preparations, and exposure to ultraviolet
light. See also 
psoriasis, guttate; psoriasis, pustu-
lar; psoriatic arthritis.