Encyclopedia of Health and Medicine

268 The Nervous System
all structures in the body. The two major divisions
of the nervous system are the CENTRAL NERVOUS SYS-
TEM and the PERIPHERAL NERVOUS SYSTEM. The central
nervous system consists of the brain and SPINAL
CORD. The peripheral nervous system consists of all
other NERVE structures, including the CRANIAL
NERVES, the SPINAL NERVES, and the PERIPHERAL
NERVES.
For further discussion of the structures and
functions of the nervous system, please see the
overview section “The Nervous System.”
See also NEURON; NEURORECEPTOR; NEUROTRANS-
MITTER.
neuralgia PAIN that occurs along a DERMATOME
(the tract of a NERVE). Neuralgia is often severe,
sharp, and brief (each episode lasting 15 seconds
or less) though repetitive. The most common
causes of neuralgia are INFECTION (notably HERPES
ZOSTER, also called postherpetic neuralgia) and
compression (a “pinched” nerve). DIABETES,
untreated (tertiary) SYPHILIS, MULTIPLE SCLEROSIS,
and PORPHYRIA are among the health conditions
that can cause neuralgia. Exposure to toxins,
notably heavy metals such as arsenic and lead,
may cause certain forms of neuralgia. Often, however,
the doctor cannot identify the cause of neuralgia.
Neuralgia may affect any dermatome in the
body. Those most often affected are the CRANIAL
NERVES that serve the face and head (especially the
glossopharyngeal, trigeminal, facial, and occipital),
the intercostal nerves (ribs), and the posterior tibial
nerve (ankle and foot).
Symptoms and Diagnostic Path
Neuralgia typically begins with sudden, sharp pain
along the affected dermatome. The attacks may be
momentarily disabling and last 10 to 15 seconds.
However, a person may experience dozens of
sequential attacks in episodes, with periods of
REMISSION during which there is no pain. The pain is
• always in the same location
• near the surface rather than deep in the body
• often intense and intermittent, though sometimes
continuous
Sometimes touching a particular area on the
SKIN or actions, such as chewing trigger, attacks of
pain. The diagnostic path includes a NEUROLOGIC
EXAMINATION and often electromyogram (EMG) to
assess the function of the nerves in the affected
area. The neurologist may conduct diagnostic
imaging procedures such as COMPUTED TOMOGRAPHY
(CT) SCAN or MAGNETIC RESONANCE IMAGING (MRI) to
determine whether there is compression of the
affected nerve, such as from a tumor, or to rule
out other possible causes of the pain.
Treatment Options and Outlook
Treatment targets the cause when known, such as
PHYSICAL THERAPY or surgery to relieve compression
against a nerve, removal from exposure to potential
toxins, or ANTIVIRAL MEDICATIONS for postherpetic
neuralgia. Tricyclic antidepressants are
particularly effective for relieving the pain of
trigeminal neuralgia. Other medications to relieve
pain include nonnarcotic and narcotic oral ANAL-
GESIC MEDICATIONS, topical analgesics such as capsaicin,
certain antiseizure medications, topical
lidocaine patches, corticosteroid/lidocaine injections
as neural blockades (nerve blocks) and TRIG-
GER-POINT INJECTION. These and other treatments
can provide relief from the symptoms of neuralgia
for most people. Taking medications, even narcotic
analgesics, on a regular schedule is usually more
effective than waiting until pain occurs or
becomes intolerable. ACUPUNCTURE and BIOFEED-
BACK are also effective for some people.
Postherpetic neuralgia generally improves and
often resolves (goes away) within 2 to 12 months as
the underlying damage to the involved dermatome
heals. Neuralgia due to other causes may persist,
particularly if the cause is chronic (such as diabetes
or MULTIPLE SCLEROSIS). When medications and other
therapies cannot control the pain (intractable neuralgia),
the neurologist or pain specialist may recommend
RHIZOTOMY, a surgical OPERATION to cut the
nerve rootlets responsible for conducting the pain
impulses. Such intervention usually, though not
always, ends the pain though may also alter sensory
perception along the dermatome.
Risk Factors and Preventive Measures
Age is the most significant risk factor for neuralgia,
particularly postherpetic neuralgia. Reduced
immune function, especially in people who have
HIV/AIDS or take IMMUNOSUPPRESSIVE THERAPY such as