Shingles

Shingles (herpes zoster) is an infection caused by the virus that causes chickenpox (varicella-zoster). One or more nerves and the skin over them are affected. Typically, the disorder causes a painful blistering rash, usually limited to one side of the body.

Shingles occurs most often between the ages of 50 and 70, but it can occur at any age. It occurs only in people who have been previously infected with the virus that causes chickenpox.

More than one third of older people with shingles have persistent pain (postherpetic neuralgia). Generally, the older a person is, the greater the chance of developing postherpetic neuralgia. Rarely, shingles leads to other serious problems.

Causes

The virus that causes chickenpox often continues to live in a person after the symptoms of chickenpox disappear. Usually, the virus lives in the part of a nerve near the spinal cord (dorsal root ganglion). Shingles develops when the virus becomes active again (is reactivated) decades later and travels down the nerve to the skin.

Most people who develop shingles have a healthy immune system. But shingles is more likely to occur when the immune system is not functioning well. As people age, the immune system becomes slightly less effective. This slight change may be all that is needed for shingles to develop. Conditions that weaken or suppress the immune system make shingles more likely to develop. These conditions include certain disorders (such as some cancers, diabetes, and HIV infection), use of drugs that suppress the immune system (immunosuppressants, such as cyclosporine and corticosteroids), and inadequate nutrition. Surgery or other trauma can trigger shingles. However, what reactivates the virus in a particular person at a particular time usually cannot be determined.

Symptoms

Usually, shingles causes abnormal sensations in the affected part of the body a few days before the rash appears. The abnormal sensations include deep pain, burning, a "pins and needles" sensation, itching, numbness, and extreme sensitivity to touch. Before the rash appears, some people have symptoms similar to those of influenza (flu), such as fever or muscle aches.

The rash may appear anywhere on the skin over the nerve in which the virus lives. The skin over a nerve is supplied (innervated) by that nerve. This area is called a dermatome. Usually, the rash is limited to an area on the trunk. But the rash can affect an arm or a leg, occasionally even fingertips or toes. In some people, the rash develops on the neck or face instead. Almost always, the rash develops on only one side of the body.

Typically, the rash begins with clusters of red bumps. Over several days, new bumps appear, tending to form a path toward the spine. Within about a day, the bumps usually turn into small, fluid-filled blisters. The skin around the blisters is usually red. The blisters are usually painful, particularly when touched.

The blisters eventually dry and scab, usually about 5 days after they appear. However, if the immune system is weakened, scabs may not develop until much later. After blisters heal, scars may form or the areas of skin may turn brownish.

If the virus spreads through the blood, scattered blisters appear on other parts of the body. Rarely, the rash spreads over much of the body or to the brain or spinal cord. Serious problems, such as confusion and partial paralysis, may result.

Shingles on the face can sometimes spread to one of the eyes. The eye may become red, swollen, painful, and very sensitive to light. Also, it may water easily. Shingles in the eye is very dangerous. Scar tissue may form on the eye. Occasionally, the eye is permanently damaged, and vision is lost.

Some people experience persistent pain (postherpetic neuralgia) for months to years after the rash resolves. The pain may be a constant, deep aching or burning. Or brief bouts of burning, sharp pain may occur. The pain may feel like an electric shock. It may be easily triggered by a light touch or a change in skin temperature.

Diagnosis and Treatment

Usually, the diagnosis is based on symptoms and the appearance of the characteristic rash. Doctors use maps of dermatomes to help them determine whether a rash is likely to be shingles. Doctors sometimes puncture one of the blisters and take a sample of the fluid inside to be analyzed in a laboratory.

See the figure The Pattern of Shingles: Dermatome Driven.

The goals of treatment are to make the rash disappear quickly, relieve pain, and prevent postherpetic neuralgia and other problems.

If treatment can be started within 3 days of the rash's appearance, doctors prescribe an antiviral drug (such as acyclovir, valacyclovir, or famciclovir), taken by mouth. The antiviral drug must be taken early if it is to make the blistering rash disappear sooner and prevent postherpetic neuralgia. A corticosteroid (such as prednisone), taken by mouth, may also be prescribed. The combination may be more effective than the antiviral drug alone. However, corticosteroids can have side effects.

Antiviral drugs taken by mouth also help when an eye is affected. If the drug is used promptly, eye damage may be less severe. In addition, corticosteroid eye drops sometimes help.

If shingles causes serious problems or is widespread or if the immune system is greatly weakened, a person may be hospitalized and treated with an antiviral drug given intravenously.

Pain is treated with pain relievers (analgesics). If pain is severe, opioids may be needed.

Burow's solution, a powder that is dissolved in cool water, can be used to soak the affected skin. This solution soothes the skin and makes the blisters dry up more rapidly. It is available without a prescription.

For postherpetic neuralgia, the effectiveness of treatment is difficult to predict. Often, several treatments need to be tried. Most people feel better after taking drugs used to control seizures (anticonvulsants, such as gabapentin). These drugs suppress painful nerve activity. Sometimes drugs used to treat depression (antidepressants, such as nortriptyline) can also suppress pain sensation. Strong analgesics may provide some relief. A cream containing capsaicin (a substance in hot red peppers) can be applied to the skin. It deadens nerves temporarily, but it causes a burning sensation that many people will not tolerate. Alternatively, a local anesthetic, such as lidocaine, can be applied to the skin as a cream, lotion, or patch. However, it is poorly absorbed through the skin, limiting its effectiveness.

If other treatments do not work, a doctor may inject a local anesthetic into the affected nerve near the spine to relieve pain. However, relief may be only temporary. Injecting a corticosteroid into the nerve may provide relief for months or longer. Electrical stimulation of nerves may be tried, but relief is often incomplete.

Outlook

The rash usually clears up in a week or two. However, if the immune system is weakened, the rash may last far longer, and serious problems are more likely. Only 10% of people with shingles develop the disorder again.

Any contact with open blisters on a person with shingles can cause chickenpox—but only in people who have never had chickenpox. If these people also have a weakened immune system, avoiding such contact is crucial. For them, chickenpox can be life threatening. People with shingles should be aware that pregnant women and infants should not come in contact with the open blisters (because the virus can harm unborn children and infants). Whether people who have been vaccinated against chickenpox have lifelong protection is not yet known.

Postherpetic neuralgia persists in about half of people over 70, despite the best treatment. The constant or unpredictable pain can disrupt nearly everything a person does. It can sometimes lead to social isolation or depression. In some people, post-herpetic neuralgia disappears, even without treatment, within a year.