Herpes Zoster Pain
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.
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 of Herpes Zoster
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.
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 (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.
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 of Post-Herpetic Neuralgia
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.
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.
We are eager to help you manage your chronic pain and appreciate your trust in us. You can learn more about our practice and the conditions we treat at www.ArizonaPain.com. To schedule an appointment please call 480-563-6400 or fax at 480-563-8009.