What is Postherpetic Neuralgia?
Postherpetic neuralgia (PHN) is a common complication that can occur long after a person recovers from the varicella-zoster virus (VZV). You may know VZV as the virus that causes chickenpox. When VZV reactivates in your body – a condition called shingles or herpes zoster – it can lead to PHN.
Before vacinations became widespread in the late 1990s to early 2000s, about 90% of U.S. adults could be tested positive for VZV. Although this number is expected to decrease, PHN remains an important subject in medicine today.
The main symptom of PHN is sharp, burning pain on one side of the body which persists for three months or longer after an outbreak of shingles. The risk of developing shingles, and consequently PHN, tends to increase with age and in individuals with suppressed immune systems. This is why older adults and infirm individuals are often the most affected.
Managing PHN often requires a combination of treatments. Many healthcare providers focus on prevention, particularly in high-risk groups, rather than cure due to the challenging nature of PHN treatment in patients who are already unwell.
What Causes Postherpetic Neuralgia?
The VZV, or Varicella-Zoster Virus, is a type of virus that has double-stranded DNA. After someone recovers from chickenpox, which is often during childhood, the VZV virus stays inactive in specific nerves in the body. It’s like it’s sleeping and doesn’t cause any problems.
However, as people get older, and their immune system isn’t as strong, the virus has the chance to wake up if there’s an added stress to the body. This could be due to either psychological stress like anxiety or physical stress like illness or injury. When the virus wakes up, it can cause Shingles, also known as Herpes Zoster (HZ).
During a Shingles outbreak, the virus copies itself and moves along nerve paths until it reaches the skin. This leads to symptoms such as blisters, skin redness, and inflammation, or swelling, in the local area.
Risk Factors and Frequency for Postherpetic Neuralgia
Postherpetic neuralgia is a condition that can develop in some people who have had a bout of acute shingles. Certain factors can increase the risk of acute shingles developing into postherpetic neuralgia. These include:
- Being older
- Having a severe immune system suppression
- Experiencing a prodromal phase (initial symptoms)
- Severe pain during the shingles outbreak
- Allodynia (a type of pain where normally non-painful stimuli cause pain)
- Eyes being affected during the shingles outbreak
- Having diabetes mellitus
According to a study in 2016, about 13% of people aged 50 and above with shingles will develop postherpetic neuralgia. The risk increases as people get older. In fact, by the age of 60, around 60% of shingles patients may develop postherpetic neuralgia, and by age 70, the percentage may rise to 75%. The chances of going on to develop postherpetic neuralgia after getting shingles are 9 to 14.3% one month after the shingles onset, 5% at three months, and 3% at one year.
Having family members who’ve had shingles can also be a risk factor. A study found that people with blood relatives who’ve had shingles had a higher chance of getting shingles themselves, compared to a control group. This risk was even higher for people who had multiple blood relatives who’ve had shingles.
A study from Iceland highlighted different risk levels based on age. It reported that patients under 50 didn’t experience severe pain at any time. On the other hand, patients over 60 experienced severe pain, with 6% at one month and 4% at three months after the onset of shingles.
It’s also worth noting that postherpetic neuralgia affects both men and women equally.
Signs and Symptoms of Postherpetic Neuralgia
Postherpetic neuralgia, a nerve pain condition, often follows an episode of shingles, more formally known as herpes zoster. Shingles usually causes a blistering rash in a specific pattern along the body’s nerves. Diagnosing postherpetic neuralgia requires identifying this history and the presence of persistent pain and sensitivity in the same area. Pain or other discomfort can last more than three months. Symptoms can include stabbing or burning pain, increased sensitivity to touch, itching, abnormal sensations, heightened pain response, or various combinations of these.
However, sometimes shingles can reactivate without a visible rash, in what is called zoster sine herpete. This can complicate matters because it affects different parts of your brain and nerves, leading to diseases like aseptic meningitis, myelitis, or cranial neuropathies.
Upon examining a postherpetic neuralgia patient, doctors may find:
- Scars from the previous shingles rash
- Changes in sensation in the affected areas, including hypersensitivity or lowered sensation
- Increased pain from normally non-painful stimuli like a light touch—a symptom known as allodynia
- Autonomic dysfunction like excessive sweating in the active area
Testing for Postherpetic Neuralgia
Postherpetic neuralgia is typically determined by examining your medical history and conducting a physical examination. In some cases, particularly when the symptoms are unusual, laboratory tests or specific images might be helpful. These might be necessary when the neuralgia doesn’t appear as expected or when the herpes zoster virus affects unusual parts of the body, such as the larynx.
Your doctor might ask for tests to measure antibodies called VZV IgG and IgM. These antibodies usually increase when your body is fighting off the herpes zoster virus. However, these tests aren’t always accurate. Sometimes the increase of these antibodies might be due to other reasons not related to the virus. The more accurate tests for detecting the virus are immunofluorescence test which looks for viruses in a sample from a blister scraping and a PCR test, that detects the virus’s DNA.
Another test would be analyzing the cerebrospinal fluid (CSF), which is the fluid in your brain and spine. In over half of people with postherpetic neuralgia, this fluid test shows changes such as increased cells (pleocytosis), increased protein, and the presence of the herpes zoster virus’s DNA. Other tests like viral culture or immunofluorescent staining can be used to tell the difference between herpes simplex and herpes zoster viruses.
Lastly, a magnetic resonance imaging (MRI) scan might be used in some cases. Small studies suggest that MRI can be effective in diagnosing complex cases of postherpetic neuralgia and differentiating it from the herpes zoster virus. In one study, MRIs revealed that over half of patients had lesions (abnormal changes or damages) in the cervical cord and the brain stem regions because of the herpes zoster virus. More than half of these patients ended up developing postherpetic neuralgia later. In the same study, patients without lesions did not develop long-term pain.
Treatment Options for Postherpetic Neuralgia
Postherpetic neuralgia, often resulting from shingles, can be addressed in three main ways. The first one is prevention, which primarily involves identifying people at high risk of getting shingles and giving them a vaccine. The second is timely detection and treatment of shingles as delaying treatment can increase the likelihood of experiencing postherpetic neuralgia. Lastly, managing postherpetic neuralgia symptoms involves multimodal medication programs and interventional procedures. However, the effectiveness of each method varies, and there is ongoing research about them.
Postherpetic neuralgia is notoriously difficult to handle for many reasons. It’s rare that symptoms completely disappear. Furthermore, many sufferers tend to be older and often have multiple existing health conditions. As such, potential side effects of various treatment options need to be carefully considered. Importantly, no single form of treatment works best for everyone. Medical professionals widely agree that combining various treatments could be the most effective strategy.
Conventional non-invasive treatments include both oral and topical medicines. A variety of medical organizations recommend oral anti-depressants, a medication called pregabalin, and a lidocaine 5% patch as initial treatments. However, given the elderly are more prone to side effects from these drugs, a structured medication plan is usually suggested. The use of opioids for pain management is controversial because of potential abuse and addiction. However, in some cases they are recommended for their effective pain relief capabilities.
Other treatment options also exist. Lidocaine patches have shown to work effectively in the short and long-term. Capsaicin preparations in patch and cream forms are other options, although their effectiveness isn’t as well proven as lidocaine. It’s important to note that capsaicin treatments can often cause pain and irritation at the application site. Other classes of medicines include non-anti-depressants and NMDA antagonists, however, current evidence supporting their usefulness is limited.
More invasive treatment methods include botulinum toxin injections, sympathetic blockade with local anesthetics, or epidural injections. The effectiveness of each varies but sometimes complete long-term symptom relief can be achieved, according to some reports. Finally, one study suggests that intrathecal medicine delivery (injecting medication into the spinal canal) is promising, resulting in significant pain relief for most of the patients who participated in the study.
What else can Postherpetic Neuralgia be?
Neuropathic pain, which is a type of pain common to many diseases and conditions, can sometimes be tricky to diagnose. Usually, if this kind of pain is felt in a certain pattern on one side of the body, near where a person has had a rash from shingles (herpes zoster), it’s a pretty clear indication of postherpetic neuralgia. But there are rare cases where other conditions causing neuropathic pain might come into play.
For instance, there has been a documented case where a condition known as Complex Regional Pain Syndrome (CRPS) affected areas of the body previously hit by shingles within just three months. The location of the neuropathic pain can give doctors clues about what’s causing it. If the pain is in the face, conditions like trigeminal neuralgia and Bell’s palsy might be the culprits. On the other hand, if what seems to be postherpetic neuralgia is located in the thoracic dermatomes (mid-body area), it could occasionally turn out to be something else, such as appendicitis, gallstones, or colitis.
In those rare cases where it’s not clear whether the pain is post-herpetic neuralgia, tests looking for the herpes zoster virus in the bloodstream could be helpful.
What to expect with Postherpetic Neuralgia
Postherpetic neuralgia can be difficult to manage. This ailment can persist for years and, in some cases, an entire lifetime. However, with the use of adult vaccines and the creation of non-live vaccine formulations, the prevention of this condition has become a realistic goal for many Americans at risk.
It’s important to manage this condition early if possible. This is because the length and intensity of the pain can increase the risk for postherpetic neuralgia. Sadly, initial treatments rarely provide long-lasting relief if the condition is well-established. For this reason, it’s suggested to consider a variety of treatment methods, based on expert advice.
While evidence is limited, there are some encouraging signs that unusual techniques (some involving surgical procedures, others not) could potentially be beneficial. These options are interesting and deserve further study.
Possible Complications When Diagnosed with Postherpetic Neuralgia
Depending on how long postherpetic neuralgia lasts and how much pain the patient experiences, they could face a variety of challenges like:
- Depression
- Feeling worn out or fatigued
- Having trouble sleeping
- Not feeling hungry
- Difficulty in focusing or concentrating
Preventing Postherpetic Neuralgia
The primary way to prevent Shingles (also known as Herpes Zoster Virus or HZV) and Postherpetic Neuralgia (PHN), which is a complication that can cause severe pain even after the Shingles rash has cleared up, is vaccination. A large study with 38,000 participants showed that Shingles vaccination in older people reduced the occurrence of Shingles by 51% and PHN by 66%. Even those who still got PHN experienced a decrease in illness severity by around 61%. However, it’s important to know that the protective effects of the vaccine may not last very long, and repeat vaccinations might be necessary to keep its power.
The original formula of the vaccine contained a weakened form of the live virus, which might theoretically cause infections in people with weakened immune systems. Therefore, its usage was limited in such vulnerable individuals. But in 2017, the FDA approved a new type of vaccine for use in people over 50. This vaccine does not contain live virus and can be used in people with weaker immunity. It also provides greater protection against Shingles and PHN compared to the original version of the vaccine.
Another method to prevent PHN is to stop Shingles from advancing to PHN, given that severe Shingles can increase the risk of PHN. Unfortunately, there’s limited evidence supporting this approach, and existing research is not well-designed enough to conclusively prove it. Currently, there’s not enough evidence to support that methods such as antiviral medications, administration of steroids, or certain medical procedures can decrease the severity of Shingles and subsequently reduce the chance of PHN. More comprehensive studies are necessary to have a more definitive conclusion on this matter.
