Webster's New World Medical Dictionary

parietal pericardium
The outer layer of the
pericardium. See also 
pericardium.
Parkinson’s disease
A slowly progressive neu-
rologic disease that is characterized by a fixed inex-
pressive face, tremor at rest, slowing of voluntary
movements, gait with short accelerating steps, pecu-
liar posture and muscle weakness (caused by
degeneration of an area of the brain called the basal
ganglia), and low production of the neurotransmit-
ter dopamine. Most patients are over 50, but at least
10 percent are under 40. Treatment involves use of
medication, such as levodopa (brand name:
Larodopa) and carbidopa (brand name: Sinemet).
A surgical procedure known as deep brain stimula-
tion, in which externally controlled electrodes are
implanted into the brain, has also been shown to be
helpful. There are no blood or laboratory tests to
diagnose the condition. Although it is a chronic and
progressive disease, the degree of disability varies
among affected persons. Also known as paralysis
agitans and shaking palsy.
paronychia
Inflammation of the folds of tissue
surrounding the nail due to infection. The infection
may be bacterial (most commonly, Staphylococcus
aureus or Streptococcus) or fungal.
parotid gland
One of the largest of the three
major salivary glands. The parotid glands are
located on the sides of the face in front of the ear,
below the level of the ear, and behind the jawbone.
See also 
parotitis.
parotitis
Inflammation of the parotid glands, a
classic feature of mumps.
paroxysmal atrial tachycardia
Bouts of rapid,
regular heart beating that originate in the upper
chamber of the heart (atrium). Abbreviated PAT.
PAT is caused by abnormalities in the atrioventricu-
lar (AV) node that lead to rapid firing of electrical
impulses from the atrium that bypass the AV node
under certain conditions, including excess alcohol
consumption, stress, caffeine use, overactive thyroid
or excessive thyroid hormone intake, and use of
certain drugs. PAT is an example of an arrhythmia in
which the abnormality is in the electrical system of
the heart, while the heart muscle and valves may be
normal. Also known as paroxysmal supraventricular
tachycardia.