all structures in the body. The two major divisions
of the nervous system are the CENTRAL NERVOUS SYS-
TEMand 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 PAINthat 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 PORPHYRIAare 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, how-
ever, the doctor cannot identify the cause of neu-
ralgia. Neuralgia may affect any dermatome in the
body. Those most often affected are the CRANIAL
NERVESthat serve the face and head (especially the
glossopharyngeal, trigeminal, facial, and occipital),
the intercostal nerves (ribs), and the posterior tib-
ial 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
REMISSIONduring 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 some-
times continuous
Sometimes touching a particular area on the
SKINor actions, such as chewing trigger, attacks of
pain. The diagnostic path includes a NEUROLOGIC
EXAMINATIONand 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) SCANor 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 THERAPYor surgery to relieve compression
against a nerve, removal from exposure to poten-
tial toxins, or ANTIVIRAL MEDICATIONSfor posther-
petic 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 cap-
saicin, certain antiseizure medications, topical
lidocaine patches, corticosteroid/lidocaine injec-
tions 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-
BACKare 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
orMULTIPLE SCLEROSIS). When medications and other
therapies cannot control the pain (intractable neu-
ralgia), the neurologist or pain specialist may rec-
ommend RHIZOTOMY, a surgical OPERATIONto cut the
nerve rootlets responsible for conducting the pain
impulses. Such intervention usually, though not
always, ends the pain though may also alter sen-
sory perception along the dermatome.Risk Factors and Preventive Measures
Age is the most significant risk factor for neural-
gia, particularly postherpetic neuralgia. Reduced
immune function, especially in people who have
HIV/AIDSor take IMMUNOSUPPRESSIVE THERAPYsuch as268 The Nervous System