Postherpetic Neuralgia

Postherpetic neuralgia (PHN) is a condition of recurring or persistent pain in an area of the body that has undergone an outbreak of herpes zoster virus (HZ), also known as the varicella-zoster virus, commonly termed shingles. It usually begins after shingles lesions (blisters) begin to crust over and heal but may occur in some patients who do not produce lesions. Some investigators suggest the pain has to be present for three months to be termed PHN.

Postherpetic neuralgia is thought to be caused by the damage or alteration of nerves that register pain, pressure, and other sensory nerves (for example, touch) that occur when the reactivated HZ viruses travel down nerves to the skin. This process first begins when the virus causes chickenpox in an individual; the viruses can infect various dorsal root ganglia (nerve cells) as chickenpox subsides. These viruses can be reactivated, usually decades later, and produce shingles lesions.

The reactivation of HZ is thought to be due to stress on the body from either another infection or an immunocompromised state (for example, some patients undergoing treatments for leukemia) that allows the HZ to escape the dorsal root cells.

PHN does not occur in everyone who gets shingles.

• About 9%-14% have symptoms after one-month post-shingles
• About 5% have PHN three months post-shingles

Age is a high-risk factor for PHN; the older a person is when they develop shingles, the more likely it is that the person will develop PHN.

• People over 60 have about a 60% chance of developing PHN after getting shingles
• People 70 or older have about a 75% chance of developing PHN after getting shingles

Another risk factor is family; people with close relatives who developed PHN are at a higher risk than those with no family history of PHN.

The main symptom is pain. The pain can be severe (allodynia - pain due to a stimulus that does not usually provoke pain); patients describe the pain as burning, sharp, jabbing, deep, and aching. Often, the patient feels increased pain when any pressure, even clothing, touches the area. Some patients describe itchy skin and weakness or paralysis of the area.

The majority of patients who are diagnosed with PHN are done by follow-up of a shingles infection or by the patient's history of a recent shingles infection. The pain is located in the same nerve distribution (dermatome) area, usually on only one side of the person's body where the shingles lesions occurred.

Treatment is individualized for each patient; no treatment is effective for all PHN patients, so clinicians often use two or more of the drug categories with examples listed below:

• Lidocaine skin patches ([Lidoderm] small, bandage-like patches applied to painful areas)
• Capsaicin skin patches ([Capsagel, Salonpas] used in a doctor's office by trained staff)
• Opioids (tramadol [Ultram], oxycodone [OxyContin], morphine)
• Anticonvulsants (pregabalin [Lyrica], gabapentin [Neurontin]) have been shown to lessen the pain of PHN probably by stabilizing abnormal electrical activity in your nervous system.
• Antidepressants (venlafaxine [Effexor], duloxetine [Cymbalta]) are often prescribed in lower doses than for depression.

Because some drugs (opioids) can be addictive and some patients may need long-term treatments (over one year), consultation with a pain-management specialist may be advised. Some individuals claim tamanu oil rubbed into the affected may reduce the symptoms of PHN. One small study and a few case reports indicate that acupuncture can help relieve the pain of PHN. Infrequently, other methods are used. TENS (transcutaneous electrical nerve stimulation) devices are designed to interrupt the body's pain sensations while nerve blocks (short-term chemical nerve sensation blockade) and nerve ablation (surgically cutting a nerve) are also used. Results vary but the methods often do not give lasting pain relief.

Only approximately 9%-15% of patients who get shingles develop PHN. For those few patients who develop PHN, the length of time that PHN lasts is variable; most PHN patients have discomfort lasting one to two months. About one-third of PHN patients have symptoms that last about three months and about one-fifth last a year or longer.

For the majority of patients who develop PHN, the prognosis is good although they may have to take pain medications for about one to three months. For others, the prognosis is fair to poor if the pain is severe, lasts longer than three months, or markedly reduces their quality of life. PHN occasionally results in permanent nerve damage; however, the disease is not fatal.

PHN itself is a complication of shingles. A severe complication of PHN is an addiction to pain medications. Some patients may be unable to live a normal lifestyle (unable to exercise) because of constant pain. In contrast, others have sleep and activities limited or even prohibited by touching the affected area, including just having contact with their clothing. Patients taking opioids may become very constipated. In a few cases of PHN, muscle weakness can be an additional complication.

If shingles can be prevented, then PHN can be prevented. Fortunately, the vaccine Zostavax is about 70% effective in preventing shingles. The CDC recommends that everyone older than 60 years of age get the vaccine; in 2011, the FDA approved the vaccine for people aged 50 and above.

The CDC states, "Zostavax should not be given to pregnant women, persons with a primary or acquired immunodeficiency, or to persons with a history of anaphylactic reaction to gelatin, neomycin, or any other component of the vaccine. Herpes zoster vaccine can be administered simultaneously with other indicated vaccines."