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Postherpetic neuralgia is a painful condition that is caused by the residual effects of shingles. It usually occurs after someone has had shingles, and the pain is confined to peripheral nerves (nerves outside the central nervous system). In a typical condition of postherpetic neuralgia, the nerve pain is restricted to an area of skin that’s innervated by a single nerve. All the painful symptoms are then felt around this area of skin, depending on the sensory nerve affected.
For a condition to be considered postherpetic neuralgia, there must have been pain localised to a specific area of skin for more than 90 days after a person has had a herpes infection that affected the same sensory nerve. Some of the symptoms include burning and shooting pain around the area, as well as increased sensation in the area.
A dermatome is an area of skin that’s supplied by a single sensory nerve. Sensory nerves originate from different levels of the spinal cord. Some of them emerge as a single nerve and then split into the motor and sensory nerves. The motor nerves supply particular muscles, and the sensory nerves supply an area of skin or dermatome. The chart of how various sensory nerves supply areas of the skin is called a dermatome map, and it’s important because it helps diagnose nerve-related conditions.
The nerves that supply a dermatome only supply that specific dermatome; they rarely cross over to supply other areas. As a result, pain confined to a specific dermatome area can be traced back to the nerve of origin, and even to the level of the spinal cord that it originates from. The dermatomes are arranged one on top of another.
For example, the nerve arising from below the seventh cervical vertebrae is responsible for supplying the area of skin on the posterior side (not the area of the palm) of the index and middle fingers, while the nerve arising from below the eighth cervical vertebrae supplies the ring and little finger.
Herpes zoster infection (also called shingles) is caused by a reactivation of the chicken pox virus in humans. The virus can lie dormant for years after the person has been cured of chicken pox. It appears as painful rashes or small blisters on the body. The herpes infection usually focuses on specific sensory nerves, and so, the rashes appear on dermatomes of the body. It appears as long stripes of red skin and pain along the dermatome can continue for months after the rash has disappeared.
The pain in postherpetic neuralgia is experienced when the virus has caused damage to the nerve involved. The shingles may lie dormant for a long time, and be triggered during periods when the immune system is suppressed, like while undergoing chemotherapy. Some postherpetic pain can develop in the absence of the herpes zoster virus. The condition in which this occurs is known as zoster sine herpete.
Pain caused by the virus that appears along specific dermatomes of the body is known as postherpetic neuralgia. However, there are other forms of neuralgia caused by other factors. Neuralgia is defined as pain and discomfort associated with a specific nerve. In conditions where the pain is localised to a specific nerve, the neuralgia takes the name of the nerve. This is opposed to postherpetic neuralgia in which a sensory nerve is affected. For example, pudendal neuralgia is damage to the pudendal nerve. It has symptoms similar to those seen in postherpetic neuralgia, like pain and discomfort along the course of a nerve. Examples of other neuralgia include Trigeminal neuralgia and Glossopharyngeal neuralgia
As mentioned, it is caused by shingles (the herpes zoster virus), which is in turn caused by a bout of chickenpox suffered in childhood. Other conditions may lead to pain along a nerve, but as explained earlier, they take the name of the nerve.
It is estimated that about one million individuals develop herpes zoster each year in the United States. One in every three people will develop shingles at some point in their lifetime. About 10% to 18% of these individuals suffer postherpetic neuralgia. It is also estimated that only about 10% of individuals below 60 years develop the painful condition. About four out of every person over the age of 60 gets postherpetic pain. This may be because older people have a weaker immune system than younger people.
The most significant risk factor for developing postherpetic neuralgia has chicken pox at a younger age. Others include
The hallmark of postherpetic neuralgia is pain along the dermatome where the shingles erupted a while after it has been cured. The pain experienced comes with different severities, and has different types of feelings in each individual.
The pain may include the following sensations
Other symptoms include
Complications of postherpetic neuralgia include
These complications are common with people who have postherpetic neuralgia for a long period. Also, the more severe the symptoms, the more likely the implications are to develop.
In most cases, postherpetic neuralgia can be diagnosed by history and physical assessment alone. A medical history of chicken pox and shingles, with a painful patch of skin that follows a dermatome, is enough for an accurate diagnosis of the condition.
This condition is originally caused by chicken pox. The pox introduces the virus into the system where it lays dormant for a long time. As a result, vaccination form chicken pox can prevent postherpetic pain. The vaccine is made from a weakened form of the zoster virus. Vaccination can decrease the overall occurrence of chicken pox and eventually lead to a reduction in the postherpetic neuralgia cases reported.
A secondary means of prevention has been proposed, but there is insufficient evidence to prove its validity. It involves the use of oral antiviral medications within 72 hours from the onset of a shingles rash. Studies and randomised control trials conducted on the use of these medications have not shown any significant effect, as people who took them are just as likely to develop postherpetic pain as people who didn’t.
No single treatment can relieve the pain of postherpetic neuralgia. Very often, a combination of treatment options is required. Also, the pain experienced in postherpetic neuralgia is very severe and causes great discomfort in people who have it. As a result, immediate action is usually taken when the condition is diagnosed. Most of the treatment of postherpetic neuralgia involves the prescription of several kinds of medications.
Medication: Anticonvulsants can be prescribed to people suffering from postherpetic pain. Even though these drugs are designed to control seizures, they are also very useful in managing postherpetic pain. Topical analgesics are also very useful. These are applied to the rash, and they are usually quite effective in managing the pain if it is mild. Oral analgesics are usually needed for more severe pain symptoms.
Skin patches can also be used to relieve the pain. Patches like lidocaine and capsaicin skin patches can be worn over the area to reduce the pain.
Brian J. Hall; John C. Hall. “Infectious diseases in the skin”. Sauer’s Manual of Skin Diseases. Lippincott Williams & Wilkins, 2010. p. 232.
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