Postherpetic neuralgia or PHN is the most common complication of shingles. It affects skin and nerve fibers and causes persistent nerve pain after an outbreak of the viral infection. Approximately one in five people with shingles also develop postherpetic neuralgia. Symptoms of PHN persist for at least one or two months after the shingles rash and blisters heal. Severe cases of PHN can last for years. There is no cure for shingles or postherpetic neuralgia, but the condition is treatable and managed with a variety of medications and interventions.

Risk Factors and Cause

The herpes varicella-zoster virus causes chickenpox. After the initial infection, the virus remains in the nervous system in a dormant or inactive state. Varicella-zoster can reactivate and cause shingles when the immune system weakens due to age, immunosuppressive medications, or illness. People over the age of 65 and those with a family history of PHN are at the highest risk of developing shingles and postherpetic neuralgia.

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The symptoms of postherpetic neuralgia occur in the same place as the initial shingles outbreak. Continuous throbbing or aching is accompanied by occasional spikes of sharp, burning pain. The skin becomes extremely sensitive to touch and temperature changes. Some people develop allodynia, which means their skin becomes so sensitive that clothing causes discomfort. Other symptoms include itching, numbness, and headaches. Muscle weakness or paralysis occurs in rare cases if the nerves that are affected control muscle movement.

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Mechanism of Action

The varicella virus itself does not cause postherpetic neuralgia. PHN only develops when the shingles outbreak damages or irritates nerve fibers. The damaged nerve cannot function properly and sends random signals to the brain. These chaotic signals cause pain at the site of the outbreak. Numbness occurs when signals do not reach the brain at all. Sometimes scar tissue forms around the damaged nerves. Scar tissue puts pressure on the nerve and causes chronic pain from inside the nervous system, which some people describe as a "pinched" or "trapped" nerve.

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Doctors diagnose postherpetic neuralgia through an examination and patient history. A diagnosis of PHN is fairly straightforward when a person sees a doctor about pain three or four months after their shingles outbreak has healed. People are more likely to develop PHN when they experience pain before the shingles rash and blisters appear. It is not clear whether any treatment during a shingles outbreak can prevent postherpetic neuralgia, because most people with shingles do not develop PHN.

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There is no standardized treatment for postherpetic neuralgia. The condition arises from a virus that causes nerve damage so that no treatment can alter its course. Several studies evaluated the effectiveness of antiviral medications administered during a shingles outbreak, with the goal of shortening the outbreak and preventing PHN. Most studies were inconclusive, and none resulted in evidence that antiviral medications can prevent PHN. Treatment is focused on managing symptoms and assisting healing. Some doctors use steroid injections to reduce inflammation, but steroids canSome not be used until the shingles rash is completely healed.

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Pain Management

Some people experience the debilitating pain of postherpetic neuralgia over a long period. Over-the-counter pain medications such as NSAIDs may relieve mild discomfort, but they are not effective for treating persistent nerve pain. Doctors may prescribe opioid pain relievers in combination with antidepressants. Anticonvulsant medications are also effective for some people with PHN. Many doctors adjust dosages and types of medication until they find a combination effective for individual patients.

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Electrical Stimulation

Other treatment options may replace or complement medications. Transcutaneous electrical nerve stimulation or TENS uses small electrical currents to disrupt pain signals. The practitioner places electrodes on adhesive pads around the affected site, and the patient turns the TENS unit on and off. Some TENS units are available for home use.

Spinal cord or peripheral nerve stimulation devices relieve some types of neuropathic pain. Doctors use thin wire electrodes to evaluate effectiveness and tolerance for each patient. If the initial tests have positive results, doctors implant small electrodes under the skin along the affected nerves. Surgeons or anesthesiologists insert simulators into the epidural space of the spinal cord and the electrodes emit a weak electric current to block pain signals.

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Patches and Topical Treatments

Some over-the-counter and prescription analgesic patches relieve burning, pain, and itching during shingles outbreaks. It is best to consult a medical professional before using any topical medications, as some may irritate the rash and blisters and cause more pain.

A treatment using chill pepper extract has been proven effective for some people with PHN. The patches cannot be used until the singles outbreak has healed completely. Then, they are applied under medical supervision. Technicians numb the skin in the affected area first, and generally monitor patients for at least an hour after removing the patch; the entire process lasts approximately two hours. The extract patches relieve pain for up to three months when the treatment is successful.

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Prognosis and Complications

Postherpetic neuralgia resolves within six to 22 months, for most people. The pain of PHN usually persists for years, and rarely, individuals experience it for the rest of their lives. Paralysis is the most severe complication of PHN. It occurs when the nerves are so badly damaged that they can not recover and function normally again. Other complications of PHN, such as insomnia and limited mobility, are a result of chronic pain. Shingles outbreaks along certain facial nerves can lead to chronic migraines or temporomandibular joint (TMJ) disorders, if PHN develops.

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Adults 50 and older should get a shingles vaccine to prevent postherpetic neuralgia, even if they have already had shingles. Multiple types of the vaccine exist and, while they are not always effective, they may offer protection. A doctor can help determine which vaccine is best on an individual basis. The vaccine can cause a headache or a mild rash, but most people do not experience any side effects.

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