What Is Postherpetic Neuralgia? What Causes Postherpetic Neuralgia?

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Main Category: Pain / Anesthetics
Also Included In: Neurology / Neuroscience
Article Date: 10 Aug 2009 - 0:00 PST

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Neuralgia is severe pain along the course of a nerve. The pain occurs because of a change in neurological structure or function due to irritation or damage of a nerve. Postherpetic neuralgia is a painful condition which affects the nerve fibers and skin. Postherpetic neuralgia is a complication of shingles.

There are two main types of pain, nociceptive and non-nociceptive pain.

An example of nociceptive pain is what you feel if somebody sticks a needle into your skin; specific pain receptors sense the needle touching your skin and breaking through. Nociceptive pain is when pain receptors sense such things as temperature, touch, vibration, stretch, and chemicals released from damaged cells.

Non-nociceptive pain, or neuropathic pain, comes from within the nervous system itself. The pain is not connected to activation of pain receptor cells in any part of the body. People often refer to it as pinched nerve, or trapped nerve. The nerve itself is sending pain messages either because it is faulty (damaged) or irritated. People with neuralgia have neuropathic pain (non-nociceptive pain).

People with postherpetic neuralgia describe the sensation as one of intense burning or stabbing pain, which often feels as if it is shooting along the course of the affected nerve.

Description of postherpetic neuralgia

Postherpetic neuralgia is a persistent nerve pain that often occurs as a result of shingles. Shingles is caused by the herpes varicella-zoster virus. This virus also causes chickenpox. Most of us get chickenpox during childhood, but after we recover the virus remains inactive in our nervous system. Our immune system stops the virus from becoming active.

However, later in life the herpes varicella-zoster virus may become reactivated, causing shingles. Shingles is an infection of a nerve and the area of skin around it - usually the nerves of the chest and abdomen on one side of the body are affected.

If the pain caused by shingles continues after the shingles is over - within two to four weeks - it is known as postherpetic neuralgia.

It is estimated that about one-in-five patients with shingles will go on to have postherpetic neuralgia.

Postherpetic neuralgia is more common as people get older - it is uncommon in children.

What are the causes of postherpetic neuralgia?

The nerve damage caused by shingles disrupts the proper functioning of the nerve. The faulty nerve becomes confused and sends random, chaotic (uncontrolled) pain signals to the brain, which the patient feels as a throbbing, burning pain along the nerve.

Experts believe that shingles results in scar tissue forming next to nerves and pressing on them, causing them to send inaccurate signals, many of which are pain signals to the brain. However, nobody is really sure why some shingles patients go on to develop postherpetic neuralgia.

What are the symptoms of postherpetic neuralgia?

Symptoms are usually limited to the area of skin where the shingles outbreak first occurred. Symptoms may include:

• Occasional sharp burning, shooting, jabbing pain
• Constant burning, throbbing, or aching pain
• Extreme sensitivity to touch
• Extreme sensitivity to temperature change
• Itching
• Numbness
• Headaches
• In rare cases, if the nerve also controls muscle movement, the patient may experience muscle weakness or paralysis.

Some patients may find the symptoms interfere with their ability to carry out some daily activities, such as bathing or dressing. Postherpetic neuralgia may also cause fatigue and sleeping difficulties.

Diagnosing postherpetic neuralgia

As postherpetic neuralgia is a complication of shingles it is easy to diagnose. If the symptoms persist after shingles, or appear after the symptoms of shingles have cleared up, then it is postherpetic neuralgia.

What is the treatment for postherpetic neuralgia?

Treatment will depend on the type of pain, as well as some aspects of the patient's physical, neurological and mental health.

• Antidepressants - these help patients with postherpetic neuralgia not because the patient is depressed, but because they affect key brain chemicals, such as serotonin and norepinephrine, which influence not only depression, but also how the body interprets pain. Dosages for postherpetic neuralgia will tend to be lower than for depression, unless the patient has both depression and postherpetic neuralgia.
  
  Examples of drugs that inhibit the reuptake of serotonin or norepinephrine are tricyclic antidepressants, such as amitriptyline, desipramine (Norpramin), nortriptyline (Pamelor) and duloxetine (Cymbalta). They will not get rid of the pain, but are said to make it more bearable.


• Anticonvulsants - as with trigeminal neuralgia pain, postherpetic pain can be lessened with anticonvulsants, because they are effective calming down nerve impulses and stabilize abnormal electrical activity in the nervous system caused by injured nerves. Gabapentin (Neurontin), pregabalin (Lyrica) are examples of commonly prescribed anticonvulsants for this type of pain.


• Steroids - a corticosteroid medication is injected into the area around the spinal cord. Injected steroids are effective for postherpetic neuralgia patients with chronic pain (persistent long-term pain). The patient should not receive this medication until the shingles pustular skin rash has completely disappeared.


• Painkillers - this may include tramadol (Ultram) or oxycodone (OxyContin). There is a small risk of dependency.


• TENS (transcutaneous electrical nerve stimulation) - electrodes are placed over the areas where pain occurs. Small electrical impulses are emitted. The patient turns the TENS device on and off as required. Some patients obtain significant pain relief from TENS, while others don't. Experts are not sure why the electrical impulses relieve pain. Some say that TENS stimulates endorphin release - endorphins are the body's natural painkillers; some people call them natural "feel good" chemicals.


• Spinal cord or peripheral nerve stimulation - similar to TENS, but here the devices are implanted under the skin, along the course of peripheral nerves. These devices are a safe, efficient, and effective way to relieve many types of neuropathic pain conditions, including trigeminal neuralgia. As soon as the electrodes are in place, they are switched on to administer a weak electrical current to the nerve. The patient will have a tingling sensation in the area. Experts believe that by stimulating the nonpainful sensory pathway, the electrical impulses trick the brain into turning off or turning right down the painful signals, resulting in pain relief.
  
  The device is surgically implanted. Before implantation doctors do a trial run using a thin wire electrode - this is to make sure the patient responds well.
  
  The spinal cord stimulator is inserted through the skin into the epidural space over the spinal cord. The peripheral nerve stimulator is placed under the skin above a peripheral nerve.


• Lidocaine skin patches - these are patches containing lidocaine - a common local anesthetic and antiarrhythmic drug. Lidocaine is also used topically (applied onto the skin) to relieve itching, burning and pain from skin inflammations, injected as a dental anesthetic, and in minor surgery. Although it is not the first line of treatment for neuralgia, it is often effective for relieving pain. The patches can be cut to fit the affected area. Lidocaine patches must not be used on the face.

Prevention of postherpetic neuralgia

Early shingles treatment - if you see your doctor as soon as any signs or symptoms of shingles appear, your chances of developing neuralgia are reduced. Aggressively treating shingles within two days of the rash appearing helps reduce both the risk of developing subsequent neuralgia or the length and severity if it does.

The only really effective way of preventing postherpetic neuralgia from developing is to protect yourself from shingles and/or chicken pox with the chickenpox (varicella) vaccine and the shingles (varicella-zoster) vaccine.

• Chickenpox vaccine - This vaccine (Viravax) is routinely given to children aged 12 to 18 months to prevent chickenpox. Experts recommend it also for adults and older children who have never had chickenpox. The vaccine does not provide 100% immunity, but it does considerably reduce the risk of complications and severity of the disease.


• Shingles vaccine - this vaccine (Zostavax) can help protect adults over 60 who have had chickenpox. It does not provide 100% immunity but does considerably reduce the risk of complications and severity of shingles. Experts recommend that people over 60 have this vaccine, regardless of whether or not they have had shingles before. The vaccine is preventative, and is not used to treat people who are infected. The following people should not have the shingles vaccine:
  
  
  • Those who have had a life-threatening reaction to gelatin, neomycin (an antibiotic), or any other shingles vaccine component.
  • People who have a weakened immune system
  • Patients receiving steroids, radiotherapy, and/or chemotherapy
  • Patients with a history of bone marrow or lymphatic cancer
  • Patients with active, untreated TB (tuberculosis)
  
  Doctors say people with a mild cold may take the vaccine, but not those who are moderately or severely ill (they should wait till they are recovered).

Written by Christian Nordqvist


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