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Postherpetic neuralgia (PHN) is a nerve pain condition (neuralgia) that may develop after an episode of herpes zoster (post-herpetic). Herpes zoster, commonly known as shingles, is caused by reactivation of the varicella zoster virus, the same virus that causes chickenpox (varicella) upon initial infection. Herpes zoster most commonly affects older adults. Approximately 1 in 5 people with herpes zoster develop PHN.
PHN is defined as moderate to severe pain that lasts for 3 months or more after a shingles rash has disappeared. Some people report pain that lasts for several years.
To diagnose PHN, your doctor will ask for your medical history, including any past shingles infections and vaccinations. They will do a physical examination, focusing on the location of pain and symptoms, and check for any changes in sensation.
The most common symptom of shingles (herpes zoster) before PHN is a painful blistering rash.
The most common signs and symptoms of PHN include:
PHN is a complication of shingles (herpes zoster). It is caused by a reactivation of the varicella zoster virus.
The first time someone is infected with this virus, it causes chickenpox (varicella). After chickenpox has resolved, the virus remains “asleep” within the nerve bundles near the spine (known as the dorsal root ganglia). The virus can remain inactive for decades, but there is a 20-30% chance it will reactivate and cause shingles later in life.
If the virus awakens, it replicates itself and travels from the nerve bundles to the skin where it forms a rash. The peripheral nerves may be damaged in the process, either directly by the virus or by inflammation. This causes initial (acute) pain in the affected area.
In some cases, the damaged nerves become irritable and continue to send exaggerated pain signals to the central nervous system. This causes the central nervous system to process pain abnormally, which leads to PHN. The pain continues after the rash has healed and can last for several months, even years.
Around 20% of people with shingles will develop PHN.
The risk increases significantly with age:
Other risk factors include:
The most effective way to prevent PHN is by vaccination. The Australian Immunisation Handbook recommends that all adults aged 60 and over should receive a single dose of the zoster vaccine, and those aged 70-79 should receive ongoing vaccination.
A single dose of the shingles vaccine is not 100% guaranteed to prevent herpes zoster, however, it does boost immunity and may reduce the risk of PHN.
Treatment with antiviral therapy during the acute phase of herpes zoster may also help to prevent PHN.
Currently approved antiviral therapies include Acyclovir, Valacyclovir, and Famciclovir. These aim to stop replication of the virus and reduce the virus “shedding” period (when the virus travels from the cell). They are effective in reducing the duration and severity of the acute pain and the time it takes for the rash to heal.
Other drugs may be prescribed in combination with antivirals to help reduce the pain and inflammation, such as glucocorticoids like prednisone.
PHN can be challenging to manage, however, there are several different treatment options available designed to target the nerve pain directly or relieve symptoms.
Anticonvulsants, also known as anti-seizure medications, are commonly prescribed for PHN because they can help stabilise abnormal nerve activity that causes pain. The two most commonly used anticonvulsants for PHN are gabapentin and pregabalin.
Certain classes of antidepressants can relieve nerve pain, even if you aren’t experiencing depression. The two main types prescribed for PHN are:
Topical treatments are applied directly to the skin over the painful area. These include:
Topical treatments are especially helpful for people sensitive to oral medications and may be ideal for elderly patients.
In cases of severe or acute PHN, slow-release opioids, such as oxycodone, tramadol, or morphine, may be prescribed. They are usually only recommended for short-term use due to their risk of side effects. Long-term use can lead to more serious complications.
Interventional therapies offer more advanced treatment options for people who don’t respond to standard treatments and continue to experience pain. These include:
Ongoing research aims to improve the effectiveness and longevity of immunity gained from the herpes zoster vaccine. More recent research focuses on enhancing the durability of the vaccine and expanding its use in immunocompromised people.
For acute herpes zoster treatment, new approaches aim to target virus replication, modulate the body’s immune response, and manage nerve activity to prevent the development of PHN.
Immunomodulatory therapies, such as monoclonal antibodies and other biologic agents, are also being researched to better control inflammation and immune responses associated with shingles.
Clinical trials continue to explore different combinations of drugs and interventional therapies to improve the management of both acute shingles and chronic PHN.
Genesis Research Services conducts clinical trials for new treatments for a range of painful conditions, including postherpetic neuralgia. To view currently recruiting studies or register your interest for future studies, click here or call us on (02) 4985 1860.
View our current studies or register your interest for future trials:
© Genesis Research Services, 2024