Encyclopedia of Health and Medicine

276 The Nervous System
• shuffling, hunched posture when walking
(Parkinsonian gait)
• loss of balance, especially when changing direction
during walking
Other symptoms develop as the condition progresses
and may include SIALORRHEA (excessive
drooling), HYPERHIDROSIS (excessive sweating), BLE-
PHAROSPASM, and difficulty speaking and swallowing.
There is no definitive diagnostic test for
Parkinson’s disease, so the diagnostic path considers
both personal health history and clinical findings.
The neurologist may conduct imaging
procedures such as COMPUTED TOMOGRAPHY (CT)
SCAN and MAGNETIC RESONANCE IMAGING (MRI) to rule
out other causes of the symptoms, such as BRAIN
TUMOR or STROKE.
Treatment Options and Outlook
Treatment targets the symptoms. Some medications
replace dopamine or function as dopamine
agonists to activate dopamine receptors. The
antiviral medication amantadine improves symptoms
in some people. Response to medications is
highly individual. The neurologist chooses medication
combinations according to the person’s
age, general health status, apparent rate of progression,
and other factors. Most people take combinations
of medications to address different
aspects of the condition and to offset the side
effects of some medications. The person eventually
becomes resistant to levodopa, a dopamine
precursor that currently is the only dopaminereplacement
DRUG available. A person who has
Parkinson’s disease can typically take levodopa for
five to seven years.
The US Food and Drug Administration (FDA)
recently approved the surgical treatment DEEP
BRAIN STIMULATION (DBS) as a treatment for Parkinson’s
disease that no longer responds to medications.
In DBS, the neurosurgeon implants an
electrode deep into the BRAIN near the thalamus (a
structure with an integral role in movement and
motor function). The electrodes connect to a pulse
generator, similar in concept to a HEART PACEMAKER,
implanted in a small pocket of tissue. The neurologist
programs the pulse generator to deliver regular
electrical impulses that subdue dyskinesias,
rigidity, and tremors. DBS can provide relief from
symptoms for a year or two with reprogramming
to adjust the intervals and intensity of the electrical
impulses.
Parkinson’s disease typically progresses over
several decades. With early treatment many people
can remain symptom free for years. As the
number of dopamine-producing cells in the brain
continues to decline, however, medications to
treat Parkinson’s disease become less effective and
eventually do not work at all. Though Parkinson’s
disease continues to progress, it is not fatal for
most people when the age of onset is 60 or later.
Risk Factors and Preventive Measures
Researchers do not know what causes Parkinson’s
disease, though it does appear to run in some families.
The most significant risk factor for Parkinson’s
disease is advancing age, as neurologists
diagnose the condition most frequently in people
who are age 60 or older. Researchers believe most
early-onset Parkinson’s disease, which often
begins in the 30s or 40s, is genetic. There are no
measures known to prevent Parkinson’s disease.
See also AGING, NEUROLOGIC CHANGES THAT OCCUR
WITH; ALZHEIMER’S DISEASE; DEMENTIA; HUNTINGTON’S
DISEASE; PALLIDOTOMY; THALAMOTOMY; TREMOR DISOR-
DERS.
peripheral nerves The nerves that branch from
the CENTRAL NERVOUS SYSTEM to serve the body. The
primary peripheral nerves are the CRANIAL NERVES
and the SPINAL NERVES, which branch into smaller
and numerous nerves that extend to all parts of
the body. The peripheral nerves may be visible to
the unaided EYE, as are the cranial nerves and the
spinal nerves, or microscopic, as are the tiny
nerves that serve areas such as the fingertips. Sensory
nerves carry signals to the BRAIN and motor
nerves carry signals to the body. Some nerves
have both functions.
For further discussion of the peripheral nerves
within the context of the structures and functions
of the nervous system, please see the overview
section “The Nervous System.”
See also SPINAL CORD.
peripheral nervous system The CRANIAL NERVES,
SPINAL NERVES, and their extensions. The peripheral
nervous system has two major subdivisions: the