called periarteritis nodosa. Areas of arter-
ial wall become inflamed, weakened, and
liable to aneurysms. The severity of the
condition depends on the arteries that
are affected and how much they are
weakened. The cause seems to be an
immune systemdisturbance, sometimes
triggered by exposure to the hepatitis B
virus. It is most common in adults and
affects men more than women.
Early symptoms of polyarteritis nodosa
include fever, aching muscles and joints,
general malaise, loss of appetite and
weight, and, sometimes, nerve pain.
There is also hypertension, skin ulcera-
tion, and gangrene. If the coronary
arteries are affected, myocardial infarc-
tionmay occur. Many patients suffer
abdominal pain, nausea, vomiting, diar-
rhoea, and blood in the faeces.
Diagnosis is made by biopsyand angio-
graphy. Large doses of corticosteroids,
and in some cases immunosuppressants,
may allow survival for at least 5 years.
Without treatment, few patients survive
for this length of time.
polycystic kidneySee kidney, poly-
cystic.
polycystic ovarySee ovary, polycystic.
polycythaemiaA condition in which
increased production of red blood cells
leads to an unusually large number of
them in the blood. This condition is
usually caused by another disorder or
by hypoxia, and is called secondary
polycythaemia. If it occurs for no appar-
ent reason, it is called polycythaemia
vera or primary polycythaemia.
Secondary polycythaemia occurs natu-
rally at high altitudes due to the
reduced oxygen level. It can also result
from a disorder that impairs the oxygen
supply to the blood, or can be secon-
dary to liver canceror some kidney
disorders. Descending to sea level, or
effective treatment of an underlying dis-
order, returns the blood to normal.
Polycythaemia vera is a rare disorder
that mainly affects people over 40. The
large number of red blood cells causes
increased volume and thickening of the
blood, which may lead to headaches,
blurred vision, and hypertension. There
may also be flushed skin, dizziness, night
sweats, and widespread itching. Thespleenis often enlarged. Possible com-
plications include a tendency to bleed
easily or to form blood clots; stroke; and
myelofibrosisor acute leukaemia (see
leukaemia, acute).
Diagnosis is made from a physical
examination andblood testsand by rul-
ing out other causes. Treatment is by
venesection, sometimes in combination
with anticancer drugsor with radioactive
phosphorus. This enables most patients
to survive for 10–15 years.polydactylyA birth defect in which
there is an excessive number of fingers
or toes. The extra digits may be fully
formed or they may be fleshy stumps.
Polydactyly often runs in otherwise nor-
mal families; however, it may also occur
as part of Laurence–Biedl–Moon syn-
drome or other congenital syndromes.
polydipsiaPersistent excessive thirst
(see thirst, excessive).
polyhydramniosExcess amniotic fluid
surrounding the fetus during pregnancy.
It occurs in about 1 in 250 pregnancies
and often has no known cause. The con-
dition sometimes occurs if the fetus has
a malformation that makes normal swal-
lowing impossible, or if the pregnant
woman hasdiabetes mellitus. The excess
amniotic fluid usually accumulates in
the 2nd half of pregnancy, producing
symptoms from about week 32. The main
symptom is abdominal discomfort. Other
possible symptoms are breathlessness
and swelling of the legs. The uterus is
larger than would usually be expected.
Occasionally, fluid accumulates rapidly,POLYCYSTIC KIDNEY POLYHYDRAMNIOSP
POLYCYTHAEMIAFLUSHED SKIN OF POLYCYTHAEMIA