Postherpetic Neuralgia (PHN)

Postherpetic Neuralgia (PHN)

Postherpetic neuralgia is nerve pain that occurs after a shingles infection. Shingles is a painful rash that appears on one area of the body, usually on the trunk or face.

Shingles is caused by the varicella-zoster virus. This is the same virus that causes chickenpox. In people who have had chickenpox, the virus can resurface years later and cause shingles.

Postherpetic neuralgia (PHN) is considered a deafferentation pain. It is defined by prolonged pain following acute herpes zoster (HZ) infection that persists beyond crusting of lesions and disappearance of the rash.

Following resolution of systemic varicella infection (which usually occurs in childhood), the virus remains dormant in the dorsal root ganglia. Later, HZ produces diffuse inflammation of peripheral nerves, dorsal root ganglion, and in some cases, the spinal cord.

Long after the acute infection resolves, the pathology reveals chronic inflammatory changes in the periphery, neuronal loss in the dorsal root ganglion, and a reduction of both axons and myelin in affected nerves.

PHN is, by definition, a persistent pain state and commonly does not resolve spontaneously. Since neuropathic pain is a common but transient feature of zoster, PHN cannot be diagnosed unless pain persists well beyond healing of the acute zoster lesions. Typically therefore it is defined as pain that persists more than 3 or 6 months after resolution of zoster. Even then, PHN can improve slowly thereafter, but it is often persistent for years or indefinitely and can be a refractory neuropathic pain. In addition to the spontaneous burning and paresthesias common to many neuropathic pain states, PHN is characteristically associated with prominent allodynia and hyperalgesia, which can often be the most disabling aspects of the condition.

How common is Postherpetic neuralgia?

The incidence of HZ is approximately 1.3 to 4.8 cases per 1000 person-years, with a higher incidence in the elderly and immunocompromised. Overall, 10% of those with acute HZ will go on to experience pain for more than 1 month, with an increasing frequency with advancing age and severity of both the rash and acute zoster pain. In one survey, the prevalence of pain 1 year after the eruption was 4.2% in patients 20 years old and younger, and 47% in those older than 70. With advent of the varicella vaccine, future studies will likely show a reduction in incidence of PHN, and at least one large trial has determined that repeat vaccination during late adulthood reduces the incidence of PHN.

How long could postherpetic neuralgia last? 

This condition varies in duration. The younger the individuals, the more likely they are to experience remission within weeks or a few months. By contrast, older patients may experience the pain indefinitely.

You may have PHN if you continue to have pain for 4 months after your shingles rash has gone away. PHN appears in the same area where you had the shingles rash. The pain usually goes away after the rash disappears.

How likely is it to be permanent or last several years? 

The incidence of postherpetic neuralgia among individuals under the age of 50 is less than 10%. By contrast, by the age of 60 the incidence jumps to 30% to 40%. Each decade above that has a higher and higher rate of getting postherpetic neuralgia for several years or permanently. For this reason, a preventive vaccine is recommended for those 60 years and older.

Getting a vaccination for shingles can prevent PHN. This vaccine is recommended for people older than 60. It may prevent shingles, and may also lower your risk of PHN if you do get shingles.

Both acute shingles and postherpetic neuralgia are severely painful. Itching or dysesthesia may precede the acute phase of zoster eruption.

By the time the eruption becomes visible, the pain intensity is in full gear. The pain is lancinating, burning, constricting, or boring in quality.

There is a background of constant pain and often a superimposed component of paroxysmal jabs.

When the skin lesion heals, the pain begins to subside—indicative of concurrent healing of the nerve and reduction in its excitability. For some individuals this could occur within a month.

For others it may extend into a second month. Those who have pain beyond this interval are said to have postherpetic neuralgia.

What are the causes?

This condition is caused by damage to your nerves from the varicella-zoster virus. The damage makes your nerves overly sensitive.

What increases the risk?

The following factors may make you more likely to develop this condition:

  • Being older than 60 years of age.
  • Having severe pain before your shingles rash starts.
  • Having a severe rash.
  • Having shingles in and around the eye area.
  • Having a disease that makes your body unable to fight infections (weak immune system).

What are the symptoms?

The main symptom of this condition is pain. The pain may:

  • Often be very bad and may be described as stabbing, burning, or feeling like an electric shock.
  • Come and go or may be there all the time.
  • Be triggered by light touches on the skin or changes in temperature.

You may have itching along with the pain.

HZ erupts in the thoracic dermatomes in more than 50% of patients. The trigeminal distribution (usually V1) is next most common. Lumbar and cervical zosters each occur in 10% to 20% of patients. PHN pain is in the same dermatomal location as the original HZ rash. The pain of PHN is described as a combination of deep aching, superficial burning, and paroxysmal pain. Itch is often reported. Allodynia or hyperpathia is common but variable; in some patients, the sensitivity to touch is the most distressing component. About 10% of patients with HZ infection experience pain without the concomitant presence of skin lesions. PHN can also occur in the ear following Ramsay-Hunt syndrome, in which varicella spreads from the geniculate ganglion.

How is this diagnosed?

This condition may be diagnosed based on your symptoms and your history of shingles. Lab studies and other diagnostic tests are usually not needed.

How is this treated?

There is no cure for this condition. Treatment for PHN will focus on pain relief. Over-the-counter pain relievers do not usually relieve PHN pain. You may need to work with a pain specialist. Treatment may include:

  • Antidepressant medicines to help with pain and improve sleep.
  • Anti-seizure medicines to relieve nerve pain.
  • Strong pain relievers (opioids).
  • A numbing patch worn on the skin (lidocaine patch).
  • Botox (botulinum toxin) injections to block pain signals between nerves and muscles.
  • Injections of numbing medicine or anti-inflammatory medicines around irritated nerves.

How do you treat acute zoster? 

Prompt initiation of antiviral therapy is recommended. Some clinicians also add corticosteroids to the regimen, especially for individuals 50 years and older.

Follow these instructions at home:

  • It may take a long time to recover from PHN. Work closely with your health care provider and develop a good support system at home.
  • Take over-the-counter and prescription medicines only as told by your health care provider.
  • Do not drive or use heavy machinery while taking prescription pain medicine.
  • Wear loose, comfortable clothing.
  • Cover sensitive areas with a dressing to reduce friction from clothing rubbing on the area.
  • If directed, put ice on the painful area:
    • Put ice in a plastic bag.
    • Place a towel between your skin and the bag.
    • Leave the ice on for 20 minutes, 2–3 times a day.
  • Talk to your health care provider if you feel depressed or desperate. Living with long-term pain can be depressing.
  • Keep all follow-up visits as told by your health care provider. This is important.

Contact a health care provider if:

  • Your medicine is not helping.
  • You are struggling to manage your pain at home.

Summary

  • Postherpetic neuralgia is a very painful disorder that can occur after an episode of shingles.
  • The pain is often severe, burning, electric, or stabbing.
  • Prescription medicines can be helpful in managing persistent pain.
  • Getting a vaccination for shingles can prevent PHN. This vaccine is recommended for people older than 60.

Sources

Williams MH, Broadley SA: SUNCT and SUNA: clinical features and medical treatment. J Clin Neurosci 15:527-534, 2008.

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