Neuralgias

What is neuralgia?

Neuralgia means burning, numbness, and pain that extends along one or more nerves. A nerve is a cord-like bundle of fibres through which sensation and motor impulses pass between the brain and the body. Neuralgia may occur in any nerve.

What are the types?

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 three branches). This condition involves sudden and short attacks of severe pain on one side of the face, along one of the areas supplied by the trigeminal nerve. The pain attacks may be severe enough to cause a facial grimace, which is classically referred to as a painful tic.

Postherpetic neuralgia: occurs after certain infections such as shingles, which is caused by the varicella-zoster virus, a type of herpesvirus. This can produce a constant burning pain after shingles rash has healed. The pain is worsened by movement or contact with the affected area.

Diabetes can produce almost any neuralgia, including:
-trigeminal neuralgia,
-carpal tunnel syndrome - a condition characterised by pain and numbness of the hand and wrist), and
-meralgia paresthetica a problem manifested by numbness and pain in the thigh, due to damage to the lateral femoral cutaneous nerve.

What are the causes?

The causes of neuralgias are varied. Chemicals can cause nerve irritation. Inflammation, trauma (including surgery), compression by adjacent structures (tumours or inflamed tissues), and infections can all lead to neuralgias. In many cases, however, the cause is unknown or unidentifiable. Neuralgias are most common in elderly persons, but they can occur at any age.

The cause of trigeminal neuralgia is occasionally a blood vessel or small tumour 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) can also cause trigeminal neuralgia, but most commonly a cause is not 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, one of the nerves that provide sensation to the throat. Symptoms of this neuralgia are short, shock-like episodes of pain located in the throat.

Postherpetic neuralgia occurs after certain infections such as shingles, which is caused by the varicella-zoster virus, a type of herpesvirus. Postherpetic neuralgia can be debilitating long after signs of the original herpes infection have disappeared. Two other infectious diseases that can cause neuralgias are syphilis and Lyme disease.

Diabetes is another common cause of neuralgias. Diabetes damages the tiny arteries that supply circulation to the nerves, resulting in nerve fibre malfunction and sometimes nerve loss.

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

What are the symptoms?

• Pain located anywhere, usually superficial (on the surface of the body)
  
• Same location for subsequent episodes
  
• 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 (resembling the effects of a local anaesthetic)
  
• Any touch or pressure is interpreted as pain. Movement may be painful.

How is the diagnosis made?

Neurologic examination shows tenderness occurring along a nerve tract. Trigeminal neuralgia causes pain usually 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 can be often encountered, such as loss of deep tendon reflexes, local loss of muscle bulk, local lack of sweating 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, 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 (NCS) with electromyography (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 overlying specific nerve paths. The doctor then figures out whether or not 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 doctor measures the electrical activity of the sampled muscle at rest and during motion, which provides, indirectly, 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 often used by physicians to determine the cause of neuralgia. Blood tests to check blood sugar and kidney function are routinely done. When the diagnosis is not clear, other tests can be helpful, particularly whenever there is suspicion of an underlying medical problem like arthritis, syphilis, vitamin deficiencies or other less common disorders. If there is concern about multiple sclerosis, usually the diagnosis can be confirmed with an imaging test of the brain such as MRI.

A lumbar puncture is often used to back up the diagnosis of multiple sclerosis and other nerve disorders. It involves inserting a needle into the lower back in order 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.

What is the treatment?

Treatment of neuralgias is aimed at reversing or controlling the cause of the nerve problem if it is identified as well as providing pain relief. Therefore, the treatment varies depending on the cause, location of the pain, 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 tumours, or surgical separation of the nerve from blood vessels or other structures that compress it.

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 painkillers, however, often have disappointing results.
Other types of medications work in different parts of the nervous system and often provide better symptom control. For eg. antiseizure medications such as carbamazepine, 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 the pain.

Other treatments may include nerve blocks, using local injections of anaesthetic 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. 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 anaesthetics 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, can result in symptom improvement. This surgical procedure consists in removing any possible compression exerted by neighbouring 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.

What is the prognosis?

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.

What are the complications?

• 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)

What is the prevention?

Treatment of associated disorders such as diabetes and renal insufficiency may prevent development of some neuralgias.