Postherpetic Neuralgia

What Is It, Causes, Symptoms, and More

Author: Lily Guo

Editors: Alyssa Haag, Ian Mannarino, MD, MBA, Kelsey LaFayette, DNP

Illustrator: Jessica Reynolds, MS

What is postherpetic neuralgia?

Postherpetic neuralgia (PHN) refers to pain occurring after the rash from shingles, also known as herpes zoster, has resolved. Shingles is caused by the reactivation of the varicella-zoster virus (VZV), the same virus that causes chickenpox. After being infected with chickenpox, the virus remains dormant in the dorsal root ganglia (i.e., a cluster of sensory neurons near the spinal cord) and can cause shingles later in life if reactivated. Shingles reactivation is more likely to occur if the individual has a weakened immune system from factors such as advanced age, HIV/AIDS, cancer, chronic stress, or corticosteroid medication. 

Vesicular rash along a dermatome.

What causes postherpetic neuralgia?

Postherpetic neuralgia is caused by an acute herpes zoster infection that has caused inflammation and subsequent fibrosis of nerves. The inflammation may induce structural changes in the affected nerves, resulting in continuous neuropathic pain. Additionally, spinal or ganglionic nerve fiber hyperexcitability and post-infectious alterations in neuronal gene expression may contribute to the ongoing neuropathic pain seen in PHN.

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What are the signs and symptoms of postherpetic neuralgia?

The signs and symptoms of postherpetic neuralgia include burning, itching, and sharp or stabbing pain isolated to one side of the body. The nerve pain can be constant or intermittent. The affected areas may show residual scarring from the vesicular rash of the preceding shingles infection or areas of excoriation caused by scratching. PHN typically involves a specific nerve and localizes to a dermatome (i.e., an area of skin innervated by a single nerve root); the contralateral nerve root and dermatomes are rarely affected. The pain is commonly localized to the trunk since the thoracic nerve fibers are often affected. Other commonly affected areas include the cervical and trigeminal nerves of the neck, arm, and face. Other common complications of shingles include allodynia (i.e., the sensation of pain evoked by normally non-painful stimuli such as light touch) and sensory deficits to thermal, tactile, pinprick, or vibratory sensation.

Postherpetic neuralgia most commonly affects those who are 60 years and older and those who are assigned female at birth. Individuals are also at a greater risk for postherpetic neuralgia if they experience more severe pain with their active shingles infection or if the rash is more severe. The pain is typically a continuation of the pain that developed during the acute episode of herpes zoster, however, in some cases, people can develop PHN months to years after the onset of the initial rash. The pain of PHN may persist for months, years, or even life, but studies have found that the mean duration of symptoms was approximately three years.

How is postherpetic neuralgia diagnosed?

The diagnosis of PHN is a clinical diagnosis based on a thorough history and physical exam. The individual may report localized sharp, burning, aching pain that has lasted more than three months in the same distribution as a previous episode of the acute herpes zoster rash. The preceding rash is described as erythematous papules (i.e., small raised bumps) and vesicles (i.e., small fluid-filled bumps) in a dermatomal distribution. The individual may also report allodynia, paresthesia, and pruritus in that same area. 

In some cases, magnetic resonance imaging (MRI) with contrast can be ordered to rule out alternative pathologies, such as radiculopathy (i.e., damage to the nerve); however, weakness is often seen on examination. MRI of the brain can be performed for individuals with pain in trigeminal or other cranial distributions to assess for secondary causes, such as neoplasm. Testing for varicella-zoster virus antibodies in the blood or cerebrospinal fluid can be useful in atypical cases to confirm past exposure to the virus; however, positive tests do not confirm PHN as the source of pain.

How is postherpetic neuralgia treated?

The first approach to PHN is the identification of at-risk populations and prevention by   administering the shingles vaccination. Early recognition and treatment of shingles is another important step to avoid PHN, as delay in recognition may increase the chance of developing PHN. Further, postherpetic neuralgia can sometimes also be prevented by treating acute herpes zoster with antiviral medicines (e.g., acyclovir)

Once postherpetic neuralgia is diagnosed, treatment aims to reduce pain and discomfort. Topical therapies for those with mild to moderate localized pain include capsaicin cream or patches, and lidocaine patches. Prescription medications can be used for moderate to severe pain and include gabapentinoids (e.g., gabapentin and pregabalin) and tricyclic antidepressants (TCAs) (e.g., amitriptyline and nortriptyline). If PHN is refractory to classic treatment, alternative medications include antiseizure medications (e.g., valproic acid, carbamazepine, oxcarbazepine) and serotonin-norepinephrine reuptake inhibitors (SNRIs) (e.g., duloxetine, venlafaxine).. Notably, once the viral infection has resolved, the use of antiviral medication has not been shown to be effective in treating PHN.

What are the most important facts to know about postherpetic neuralgia?

Postherpetic neuralgia refers to the persistent pain that can occur after a shingles infection. PHN is thought to be caused by nerve inflammation and fibrosis. Pain is typically one-sided and dermatomal, often on the trunk. PHN typically affects older adults, with a higher risk in those with more severe shingles outbreaks. Duration varies, averaging around three years. Diagnosis relies on clinical assessment and prevention involves antivirals and vaccination. Treatment includes topical therapies and prescription medications for mild to moderate cases, while anti-seizure medications and SNRIs are used for refractory cases. 

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Related links

Herpes zoster infection (shingles): Clinical sciences
Nonbenzodiazepine anticonvulsants
Varicella zoster virus

Resources for research and reference

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VisualDx Herpes Zoster.