pneumonitisInflammation of the lungs
that may cause coughing, breathing diffi-
culty, and wheezing. Causes include an
allergic reaction to dust containing ani-
mal or plant material (see alveolitis) and
exposure to radiation (see radiation haz-
ards). Pneuomonitis may also occur as a
side effect of drugs, such as amiodarone
andazathioprine.
pneumothoraxA condition in which air
enters the pleural cavity (the space
between the layers of the pleura). Symp-
toms are chest pain or shortness of
breath. If air continues to leak, the pneu-
mothorax may grow to produce a tension
pneumothorax. This may be life-threat-
ening. Diagnosis is confirmed by chest
X-ray. A small pneumothorax may dis-
appear in a few days without treatment.
If not, treatment involves removing the
air through a tube with a one-way valve.
pocket, gingivalSee periodontitis.
podiatryA paramedical speciality con-
cerned with the feet (see chiropody).
podophyllinA drug used to treat geni-
tal warts (see warts, genital). It may
cause irritation of thetreated area and
severe toxicity on excessive application.
poisonA substance that, in relatively
small amounts, disrupts the structure
and/or function of cells. (See also drug
poisoning; poisoning.)
poisoningPoisonsmay be swallowed,
inhaled, absorbed through skin, or inject-
ed under the skin (as with an insect
sting). Poisons may also originate in the
body, as when bacteria produce endotox-
ins, or when metabolic disordersproduce
poisonous substances or allow them to
build up. Poisoning may be acute (a
large amount of poison over a short
time) or chronic (gradual accumulation
of poison that is not eliminated quickly).
Unintentional poisoning occurs mainly
in young children. Adults may be poi-
soned by mistaking the dosage of a
prescribed drug (see drug poisoning), by
taking very high doses of vitamin or
mineral supplements, by exposure to
poisonous substances in industry, or by
drug abuse. Poisoning may also be a
deliberate attempt to commit suicide.
polioAn abbreviation for poliomyelitis.
poliomyelitisAn infectious viral dis-
ease,also called polio. It is usually
mild, but in serious cases, it attacks the
brain and spinal cord, sometimes caus-
ing paralysis or death. The virus is spread
from the faeces of infected people to
food. Airborne transmission also occurs.
In countrieswith poor hygiene and sani-
tation, most children develop immunity
through being infected early in life,
when the infection rarely causes serious
illness. In countries with better stan-
dards, this does not occur and, if
children are not vaccinated, epidemics
can occur. In the UK, polio is now very
rare due to a vaccination programme.
Most infected children have no symp-
toms. In others, there is a slight fever,
sore throat, headache, and vomiting
after a 3–5-day incubation period. Most
children recover completely, but inflam-
mation of the meningesmay develop.
Symptoms are fever, severe headache,
stiff neck and back, and achingmuscles,
sometimes with widespread twitching.
Often, extensive paralysis, usually of the
legs and lower trunk, occurs in a few
hours. If infection spreads to the brain-
stem, problems with, or total loss of,
swallowing and breathingmay result.
Diagnosis is made by lumbar puncture,
throat swab, or a faeces sample. Charac-
teristic paralysis with an acute feverish
illness allows an immediate diagnosis.
There is no effective drug treatment for
polio. Nonparalytic patients usually need
bed rest and analgesic drugs. In paraly-
sis, physiotherapyand, in some cases,
catheterization, tracheostomy,and artifi-
cial ventilation are needed.
Recovery from nonparalytic polio is
complete. More than half of those with
paralysis make a full recovery, fewer
than a quarter are left with severe dis-
ability, and fewer than 1 in 10 dies.
In the UK, vaccination against polio is
given at about age 2, 3, and 4 months,
with a booster dose at about 5 years
(see immunization). Parentsand carers
should also be immunized because the
active vaccine can cause polio.
pollutionContamination of the environ-
ment by poisons, radioactive substances,
microorganisms, or other wastes.
poly-A prefix meaning many or much.
polyarteritis nodosaAn uncommon
disease of medium-sized arteries, alsoPNEUMONITIS POLYARTERITIS NODOSA
P