PHN - Postherpetic Neuralgia

Postherpetic neuralgia is a pain that persists in some people who have had shingles. It often eases and goes over time. Medication can often ease the pain.

What is postherpetic neuralgia?

Postherpetic neuralgia (PHN) is a nerve pain (neuralgia) that persists after a shingles rash has cleared. If the pain goes, but then returns at a later date, this too is called PHN.

Shingles is an infection of a nerve, and causes a typical rash. It is caused by the varicella-zoster virus. About 1 in 5 people have shingles at some time in their life. Shingles can occur at any age, but it is most common in people aged over 50. Most people with shingles have pain, but the pain usually eases soon after the rash clears. PHN is pain that persists. (See separate leaflet called Shingles (Herpes Zoster) for details about shingles.)

How common is postherpetic neuralgia?

PHN is unusual in people aged under 50, and if it does occur it tends to be mild. PHN is more likely to develop, and is more likely to be severe, in people aged over 60. About 1 in 4 people aged over 60 who have shingles develop PHN that lasts more than 30 days. The older you are, the more likely it is that it will occur. However, early treatment of shingles can reduce the risk of developing PHN.

What are the symptoms of postherpetic neuralgia?

PHN causes pain on and around the area of skin that was affected by the shingles rash. The pain is mild or moderate in most cases. However, the pain is severe in some cases.

The pain is usually a constant, burning, or gnawing pain. In addition to, or instead of this, you may have sharp or stabbing pains that come and go. The affected area of skin is often very sensitive. Even slight touch may cause pain, such as the rubbing of clothes or a draught of air on the affected area. You may also have reduced sensation to touch, and be itchy over the affected area.

Why does the pain persist in some people?

Shingles causes inflammation of the nerve. Pain can be expected whilst the rash and inflammation occur. However, it is not clear why some people continue to have pain when the inflammation has gone. It is thought that some scar tissue next to the nerve, or in the nearby part of the spinal cord, may be a factor. This may cause pain messages to be sent to the brain.

Will the pain go away?

Without treatment, PHN typically eases gradually and goes. In about 5 in 10 people with PHN, symptoms are gone by three months. However, without treatment, about 3 in 10 people with PHN still have pain after a year. Some people have a slow improvement over a long period of time. A small number of people do not have any improvement over time.

What are the treatments for postherpetic neuralgia?

General measures

Loose-fitting cotton clothes are best to reduce irritation of the affected area of skin. Pain may be eased by cooling the affected area with ice cubes (wrapped in a plastic bag), or by having a cool bath. Some people find that putting several layers of 'cling film' over the affected area of skin helps. This allows clothes to slide over the skin without irritating.

Commonly used traditional painkillers

You may have already tried traditional painkillers such as paracetamol or anti-inflammatory painkillers such as ibuprofen that you can buy from pharmacies. However, these are unlikely to ease PHN very much in most cases.

Antidepressant medicines

An antidepressant medicine in the tricyclic group is a common treatment for PHN. It is not used here to treat depression. Tricyclic antidepressants ease nerve pain (neuralgia) separately to their action on depression. There are several tricyclic antidepressants, but amitriptyline is the one commonly used for nerve pain. Pain is stopped, or greatly eased, in up to 8 in 10 cases of PHN treated with amitriptyline. Imipramine and nortriptyline are other tricyclic antidepressants that are sometimes used to treat PHN.

A tricyclic antidepressant will usually ease the pain within a few days, but it may take 2-3 weeks. It can take several weeks before you get maximum benefit. Some people give up on their treatment too early. It is best to persevere for at least 4-6 weeks to see how well the antidepressant is working. If an antidepressant works, it is usual to take it for a further month after the pain has gone or eased. After this, the dose is gradually reduced and then stopped. You should re-start the antidepressant quickly if the pain returns.

Tricyclic antidepressants sometimes cause drowsiness. This often eases in time. To try to avoid drowsiness, a low dose is usually started at first, and then built up gradually if needed. A dry mouth is another common side-effect. Frequent sips of water may help with this.

Anti-epileptic medicines (anticonvulsants)

An anti-epileptic medicine is an alternative to an antidepressant. For example, gabapentin, pregabalin, sodium valproate, oxcarbazepine and carbamazepine. These medicines are commonly used to treat epilepsy but they have also been found to ease nerve pain. An anti-epileptic medicine can stop nerve impulses causing pains separate to its action on preventing epileptic seizures. As with antidepressants, a low dose is usually started at first and built up gradually, if needed. It may take several weeks for maximum effect as the dose is gradually increased.

Opiate (strong) painkillers

Opiate painkillers are the stronger traditional painkillers. For example, codeine, morphine and related medicines. As a general rule, they are not used first-line for neuropathic pain. This is partly because there is a risk of problems of medication dependence, impaired mental functioning and other side-effects with the long-term use of opiates. Also, the medicines listed above tend to work better anyway for neuropathic pain. However, tramadol is often used.

Tramadol is a painkiller that is similar to opiates but has a distinct method of action that is different to other opiate painkillers. A recent research review concluded that tramadol may be a good option for neuralgic pain in certain situations.

Combinations of medicines

Sometimes both an antidepressant and an anti-epileptic medicine are taken if either alone does not work very well. Sometimes tramadol is combined with a tricyclic antidepressant or an anti-epileptic medicine. As they work in different ways, they may complement each other and have an additive effect on easing pain better than either alone.

Topical lidocaine (lidocaine patches)

Lidocaine is normally used as a local anaesthetic. Lidocaine patches contain a special gel allowing the active ingredient, lidocaine, to seep into your skin. The aim is for the lidocaine to block the pain signals coming from the nerve. Lidocaine patches are not usually advised as a 'first-line' treatment. However, they may be considered for people when other treatment options have not worked well, are unsuitable, or have caused bad side-effects. You wear a patch for 12 hours (day or night as you prefer) on or near the painful area and leave the skin open to breathe for the other 12 hours.

Capsaicin cream

This is sometimes tried if the above treatments do not help, or cannot be used because of problems or side-effects. Capsaicin is thought to work by blocking nerves from sending pain messages. Capsaicin cream is applied 3-4 times a day. Wash your hands immediately after applying it. It can cause an intense burning feeling when it is applied; in particular, if it is used less than 3-4 times a day, or if it is applied just after taking a hot bath or shower. (However, this side-effect tends to ease off with regular use.) Capsaicin cream should not be applied to broken or inflamed skin. It is therefore not suitable for use during an episode of shingles. It should only be used on healthy skin which is painful due to PHN.

Treatment for itch

Some people have a severe itch with PHN. This is difficult to treat. An antihistamine taken at bedtime may help you to sleep better and reduce the scratching that you may do in the night (which may then make the itch less severe the following day).

Side-effects and titrating dosages of medicines

For most of the medicines listed above it is common practice to start at a low dose at first. This may be sufficient to ease the pain but often the dose needs to be increased if the effect is not satisfactory. This is usually done gradually and is called titrating the dose. Any increase in dose may be started after a certain number of days or weeks - depending on the medicine. Your doctor will advise as to how and when to increase the dose if required; also, the maximum dose that can be taken for each particular medicine.

The aim is to find the lowest dose required to ease the pain. This is because the lower the dose, the less likely that side-effects will be troublesome. Possible side-effects vary for the different medicines used. A full list of possible side-effects can be found with information in the medicine packet. Some people don't get any side-effects, some people are only mildly troubled by side-effects that are OK to live with, but some people are troubled quite badly by side-effects. Tell your doctor if you develop any troublesome side-effects. A switch to a different medicine may be an option if this occurs.

Can shingles and postherpetic neuralgia be prevented?

Shingles can only be prevented if you never have chickenpox, or if you have very good immunity against the chickenpox virus (that is, against the varicella-zoster virus). Most people in the UK have chickenpox as a child. However, there is a vaccine against the varicella-zoster virus which has been used routinely in children in the USA since 1996. It is not given routinely in the UK. The vaccine has reduced the incidence of chickenpox in the USA. Time will tell if this has a knock-on effect of reducing the incidence of shingles when these children are older.

Immunisation for older people

A trial of the vaccine against the chickenpox virus, given to people aged 60, was reported in 2005. The theory is that the vaccine given at this age would boost the waning immunity against the virus. This may help to reduce the risk of developing shingles in older age. The result of the trial was very encouraging. It found that the number of cases of shingles and PHN was reduced in those who were immunised compared with those not immunised.

A much larger research trial of the vaccine was published in 2011. This confirmed that the risk of older people developing shingles is greatly reduced by immunisation. The research trial compared 75,000 older people, who had been immunised, against over 200,000 older people who had not been immunised. The subsequent rate of shingles in the immunised group was about 6 per 1,000 per year. But this was much lower than the rate of 13 per 1,000 per year in the group not immunised. So, immunisation does not guarantee that you won't get shingles, but seems to reduce the risk of developing shingles by about 50%.

From September 2013 a shingles vaccine (Zostavax®) will be offered to adults aged 70-79 years in the UK.