The causes of neuralgia are varied. Chemical irritation, inflammation, trauma (including surgery), compression by nearby structures (for instance, tumors), and infections may all lead to neuralgia. In many cases, however, the cause is unknown or unidentifiable.

Neuralgia is most common in elderly persons, but it may occur at any age.

Trigeminal neuralgia is the most common form of neuralgia. It affects the main sensory nerve of the face, the trigeminal nerve ("trigeminal" literally means "three origins", referring to the division of the nerve into 3 branches). This condition involves sudden and short attacks of severe pain on the side of the face, along the area supplied by the trigeminal nerve on that side. The pain attacks may be severe enough to cause a facial grimace, which is classically referred to as a painful tic (tic douloureux).

Sometimes, the cause of trigeminal neuralgia is a blood vessel or small tumor pressing on the nerve. Disorders such as multiple sclerosis (an inflammatory disease affecting the brain and spinal cord), certain forms of arthritis, and diabetes (high blood sugar) may also cause trigeminal neuralgia, but a cause is not always identified.

In this condition, certain movements such as chewing, talking, swallowing, or touching an area of the face may trigger a spasm of excruciating pain.

A related but rather uncommon neuralgia affects the glosso-pharyngeal nerve, which provides sensation to the throat. Symptoms of this neuralgia are short, shock-like episodes of pain located in the throat.

Neuralgia may occur after infections such as shingles, which is caused by the varicella-zoster virus, a type of herpesvirus. This neuralgia produces a constant burning pain after the shingles rash has healed. The pain is worsened by movement of or contact with the affected area.

Postherpetic neuralgia may be debilitating long after signs of the original herpes infection have disappeared. Other infectious diseases that may cause neuralgia are syphilis and Lyme disease.

Diabetes is another common cause of neuralgia. This very common medical problem affects almost 1 out of every 20 Americans during adulthood. Diabetes damages the tiny arteries that supply circulation to the nerves, resulting in nerve fiber malfunction and sometimes nerve loss.

Diabetes can produce almost any neuralgia, including trigeminal neuralgia, carpal tunnel syndrome (pain and numbness of the hand and wrist), and meralgia paresthetica (numbness and pain in the thigh due to damage to the lateral femoral cutaneous nerve). Strict control of blood sugar may prevent diabetic nerve damage and may accelerate recovery in patients who do develop neuralgia.

Other medical conditions that may be associated with neuralgias are chronic renal insufficiency and porphyria -- a hereditary disease in which the body cannot rid itself of certain substances produced after the normal breakdown of blood in the body. Certain drugs may also cause this problem.

• Pain located anywhere, usually on or near the surface of the body
  • In the same location for each episode
  • Sharp, stabbing pain or constant, burning pain
• Pain along the path of a specific nerve
• Impaired function of affected body part due to pain, or muscle weakness due to concomitant motor nerve damage.
• Increased sensitivity of the skin or numbness of the affected skin area (feeling similar to a local anesthetic such as a Novacaine shot)

Any touch or pressure is interpreted as pain. Movement may also be painful.

Neurologic examination shows tenderness occurring along a nerve tract. Trigeminal neuralgia usually causes pain along the second and third nerve divisions (lower face and jaw), and rarely involves the first nerve division (temple and forehead). Other signs of altered nerve function may be often encountered, such as loss of deep tendon reflexes, local loss of muscle bulk, local lack of sweating (sweating is regulated by nerve function), and abnormal skin sensation.

There may be specific trigger points (areas where even a slight touch triggers pain). A dental examination is used to rule out dental disorders that may cause facial pain. The presence of other symptoms (such as redness or swelling) may indicate disorders causing the pain, such as infections, bone fractures, rheumatoid arthritis, or other disorders.

No tests are specific for neuralgia, but tests may be used to rule out other causes of the pain. Sometimes a nerve conduction study with electromyography (NCS/EMG), which examines the electrical activity of nerves, may confirm the diagnosis.

The first part of the test, the NCS, involves giving small electric shocks to skin areas overlaying specific nerve paths. The physician then determines whether the conduction of electricity is delayed or blocked through the particular nerve that was tested.

The second part of the test, the EMG, involves the careful insertion of a very fine needle into the skin, which is attached to an electric probe. The measure of electrical activity of the sampled muscle at rest and during motion indirectly provides useful clues regarding nerve function. Although the procedure sounds rather unpleasant, most patients are able to tolerate it with little discomfort.

There are a number of other laboratory tests doctors use to determine the cause of neuralgia. Blood tests to check blood sugar and kidney function are routinely used. When the diagnosis is not clear, other tests may be helpful -- particularly whenever there is suspicion of an underlying medical problem like arthritis, syphilis, vitamin deficiencies, or other less common disorders. If multiple sclerosis is suspected, the diagnosis usually can be confirmed with an imaging test of the brain such as MRI.

A lumbar puncture (spinal tap) is often used to confirm the diagnosis of multiple sclerosis and other nerve disorders. It involves inserting a needle into the lower back to reach a spot called the subarachnoid space, which is filled with cerebrospinal fluid (CSF). Analysis of this fluid may show evidence of inflammation, helping to establish the correct diagnosis.

Treatment of neuralgia is aimed at reversing or controlling the cause of the nerve problem (if identified) as well as providing pain relief. Therefore, the treatment varies depending on the cause, location, and severity of the pain and other factors. Even if the cause of the neuralgia is never identified, the condition may improve spontaneously or disappear with time.

The cause (if known) should be treated. This may include surgical removal of tumors, or surgical separation of the nerve from blood vessels or other structures that compress it.

Mild over-the-counter analgesics such as aspirin, acetaminophen, or ibuprofen may be helpful for mild pain. Narcotic analgesics such as codeine may be needed for a short time to control severe pain. These traditional pain-killers, however, often have disappointing results.

Other types of medications work in different parts of the nervous system and often provide better symptom control. For instance, antiseizure medications such as carbamazepine, gabapentin, lamotrigine or phenytoin may be helpful for pain associated with trigeminal neuralgia. The most common adverse effects of antiseizure drugs are drowsiness, tremor, and incoordination.

Antidepressant medications, such as amitryptiline, may be helpful to control pain in some cases. The topical (local) application of creams containing capsaicin also may help to control pain.

Other treatments may include nerve blocks, local injections of anesthetic agents, or surgical procedures to decrease sensitivity of the nerve. Some procedures involve the ablation (surgical destruction) of the affected nerve using different methods, such as local radiofrequency, heat (thermocoagulation), balloon compression, and injection of chemicals (such as glycerolysis).

Unfortunately, these procedures do not guarantee improvement and can cause sensory loss or abnormal sensory phenomena.

Another strategy sometimes used for resilient cases of neuralgia is called motor cortex stimulation (MCS), which consists of surgically placing an electrode over the sensory cortex of the brain. The electrode is hooked to a pulse generator pocketed under the skin. Such surgical procedures, however, are tried only when more conservative approaches have failed.

For postherpetic neuralgia, injections of anesthetics and steroids (potent anti-inflammatory drugs) in the subarachnoid space through a spinal tap may provide pain relief. For both trigeminal and glosso-pharyngeal neuralgias, a procedure called microvascular decompression, may result in symptom improvement. This surgical procedure consists of removing any possible compression exerted by neighboring blood vessels over the affected nerve.

Physical therapy may be helpful for some types of neuralgia, especially postherpetic neuralgia. Treatment of shingles with antiviral medication may decrease the incidence of postherpetic neuralgia.

Most neuralgias are not life-threatening and do not indicate other life-threatening disorders. However, pain can be severe and in some cases, incapacitating. For severe pain, be sure to see a pain specialist so that all options for treatment can be explored.

Most neuralgias will respond to treatment. Attacks of pain are usually episodic (occurring in intervals, alternating with relatively pain-free periods of time). However, attacks may become more frequent in some patients as they age.

• Unnecessary dental procedures prior to diagnosis of neuralgia
• Disability caused by pain
• Complications of surgery
• Side effects of medications used to control pain (see the specific medication)