Herpes
zoster (also known as shingles) is an acute viral disease caused by the
same virus that causes chicken pox in children. It primarily affects
the dorsal root ganglia of the spinal nerves or a division of the
trigeminal nerve. There are over 300,00 new cases annually in the
United States. The virus multiplies in the dorsal root ganglion and is
transported along the sensory nerves to the nerve endings in the skin
where the characteristic lesions are formed.
Herpes zoster
represents the unmasking of the dormant virus, which has resided in the
dorsal root ganglion since the original infection. The disease
increases sharply in incidence in the elderly and the
immuno-compromised or chronically-ill patient. Men are affected more
commonly than women.
Clinical Presentation
The
disease usually follows a dermatomal distribution. The first signs are
pain and paresthesias, followed shortly in several days by a vesicular
rash. These vesicles usually scab over within one week and are healed
in one month. At the same time, an intense necrotizing reaction is seen
in the dorsal root ganglion of the spinal cord, with virus particles
being transported through afferent fibers to the skin.
The
pain ranges from mild to severe, with a burning and shooting component.
Paresthesias may also be present. Four to five days after symptoms
start, vesicles appear in the same dermatomal distribution. Severity of
pain continues to worsen, and can be aggravated by movement or touch.
The
diagnosis of herpes zoster is difficult to make before the vesicles
have formed. The disease can be mistaken for angina, pleurisy,
appendicitis, cholecystitis or peritonitis. However, after eruption of
the vesicles the clinical picture becomes typical. The vesicles then
dry and crusts form, which progress slowly over several weeks to healed
skin.
Acute herpes zoster usually has a dermatomal
distribution, most often unilateral. The most common areas of
involvement are the thoracic areas, followed by trigeminal distribution
(usually the ophthalmic division), followed by lumbar and cervical
involvement. Bilateral disease rarely occurs.
Treatment
Treatment
goals in the immuno-competent patient are to reduce the pain and
prevent post-herpetic neuralgia. Patients may be given an anti-viral
agent. One of the most commonly prescribed medications is Famvir. These
agents work by interfering with viral DNA synthesis. However, they must
be given early in the progression of the disease prior to significant
tissue damage. When anti-viral therapy is initiated early, it has been
shown to promote healing of lesions, and possibly reduce the incidence
of post-herpetic neuralgia.
Non-steroidal anti-inflammatory
medications can be used for mild discomfort. If the pain is moderate to
severe, narcotic medications can be considered. Usually, the period of
acute herpes zoster pain is brief and narcotic therapy is necessary for
a limited period. These medications include darvocet, vicodin and
lortabs.
Injection therapy consists of sympathetic blocks and
local infiltration with local anesthetic and steroids (usually
triamcinolone). In several studies, local infiltration has achieved
excellent results in almost 100% of the patients, with a corresponding
decrease in the incidence of post-herpetic neuralgia. The technique
involves subcutaneous injection of local anesthetic containing
triamcinolone directly at the site of the lesions.
Sympathetic
nerve blocks have recently been shown to dramatically decrease the pain
associated with the acute phase of herpes zoster. Of greater value,
however, is the evidence that indicates early sympathetic blocks can
significantly reduce the incidence of post-herpetic neuralgia.
The
chief determining factor for the success of the treatment appears to
depend on how soon after the start of symptoms the sympathetic block is
performed. For sympathetic blocks performed within two weeks of the
onset of symptoms, almost 100% success is achieved.
As the
disease progresses, or post-herpetic neuralgia develops, the success
decreases to 30%. Therefore, the evidence suggests that the sooner the
therapy is instituted, the greater the chance of successful treatments.
Sympathetic blocks can be achieved by a variety of means. For
herpes zoster of the trigeminal nerve, a stellate ganglion block will
provide sympathetic blockade. For herpes zoster of the thoracic and
lumbar regions, an epidural block at the appropriate spinal level can
provide a sympathetic block.
Conclusion
Herpes zoster is a significant pain problem in
the American population. The key to management of this problem is early
diagnosis and treatment. Correct management will lead to significant
pain reduction and may also lower incidence of post-herpetic neuralgia.
POST-HERPETIC NEURALGIA
Post-herpetic neuralgia (PHN) is a
painful condition that occurs in patients following an acute herpes
zoster infection (shingles). PHN may persist for months or years after
the original skin lesions have healed. The incidence of PHN after an
outbreak of shingles is 10% in patients over 40 years, and 20-50% in
patients over 60 years. PHN is rarely seen in patients under 30 years,
and then usually resolves in 1-2 weeks. This is one of the most
difficult problems encountered by physicians. Few other conditions
create such agonizing pain and suffering for the patient. Many patients
consider suicide as a means of relief from the torturous pain.
Clinical Presentation
It
is possible to confuse PHN with other medical problems, but the patient
usually has a history of a previous unilateral skin eruption typical of
shingles. PHN is said to occur when the discomfort of herpes zoster
persists one month after the rash has healed. The skin may be
erythematous and scarred. Sensory abnormalities are common. The patient
may demonstrate tactile allodynia (normally painless touch is perceived
as painful), hyperesthesia (increased sensitivity to stimulation) or
dysesthesia (abnormal sensations such as burning or tingling) in the
affected area. Pain is typically described as constant, shooting,
burning or gripping with frequent paroxysms of lancinating pain. There
are no pain-free intervals.
The hyperpathia experienced by the
patient usually indicates damage to a peripheral nerve, the
spinothalamic tract or the thalamus. It may be caused by a reduction in
the number and proportion of conducting nerve fibers. The skin may be
so sensitive that patients cut holes in their clothes to relieve
pressure. A slight breath of wind can cause a paroxysm of pain. The
most common sites of involvement are the thoracic region, followed by
face (ophthalmic division) and cervical area. For unknown reasons, PHN
in the ophthalmic division of the trigeminal nerve are often the most
difficult lesions to treat successfully.
Treatment
The
best treatment for post-herpetic neuralgia is early, aggressive
treatment of acute herpes zoster infections. Shortening the duration of
the acute viral phase, combined with adequate pain relief may minimize
the potential for PHN. Once the condition is established, treatment
includes three general goals: 1) provide relief of pain, 2) reduce
depression and anxiety, and 3) decrease insomnia.
Drug therapy
involves multiple classes of drugs, including analgesics,
anti-depressants, tranquilizers, anti-convulsants and topical
preparations. As a rule, anti-viral agents are inappropriate in the
treatment of PHN. Opioid analgesics may relieve a portion of the pain,
but rarely are effective for the hyperpathia and dysesthesias. Elavil
is a tricyclic anti-depressant and has been shown effective for
treatment of PHN and other chronic pain syndromes. The pain-relieving
effect of Elavil is considered independent of the anti-depressant
effect. Topical preparations include capsaicin, lidocaine gel and EMLA
cream.
Nerve blocks serve to provide immediate pain relief and
block the autonomic response to noxious stimulation. They break the
cycle of this disease. Early use of nerve blocks may give protracted
relief by limiting input into damaged areas of the spinal cord, thus
decreasing the potential for development of self-perpetuating central
pain mechanisms. As the syndrome becomes more established, nerve blocks
become less effective because of centralization of pain-initiating
mechanisms.
Local Infiltration: Subcutaneous infiltration of
local anesthetics and steroids can relieve considerable amounts of pain
and burning. Most cases of PHN require 4 to 10 treatment sessions, and
can provide prolonged relief and avoid further more aggressive therapy.
Moderate to significant improvement is obtained in 70% of the patients.
Epidural Injections: These injections have been shown to
provide significant pain relief for cervical, thoracic and lumbar
distributions of PHN. The affected spinal segment are identified, then
3-4 epidural injections of local anesthetics and methylprednisilone are
performed on a weekly basis. The earlier this treatment is initiated,
the higher the success rate.
Sympathetic Nerve Blocks:
Sympathetic nerve blocks have an impressive therapeutic effect in early
herpes zoster, with rapid resolution of the acute illness and
prevention of post-herpetic neuralgia. The use of sympathetic blocks in
the early stages of PHN may also be extremely effective for pain
reduction. For the neck and head, blocks of this type include the
stellate ganglion block. Good pain relief can be obtained when
solutions containing local anesthetics are injected at 3-4 day
intervals.
Conclusions
Post-herpetic neuralgia
is a common and difficult pain problem. There is a close relationship
between the duration of neuralgia and therapeutic efficacy. Prompt
treatment shortens the progressive course of the disease and also
decreases its severity.
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