Publié par happy-diet jeudi 20 mai 2010

Trigeminal Neuralgia

Gamma Knife for Trigeminal NeuralgiaTrigeminal neuralgia (TN), also known as “tic douloureux” (pronounced “tick-doo-la-roo”), is a condition affecting the trigeminal nerve or fifth cranial nerve. This nerve is one of the largest in the head and is responsible for sending impulses of touch, pain, pressure, and temperature to the brain from the face, jaw, gums, forehead, and around the eyes. Trigeminal neuralgia is characterized by sudden attacks of pain to the face, commonly described as sudden, severe, electric-shock-like, or stabbing. Most often the pain is felt only on one side of the face, jaw, or cheek, but it can affect both sides of the face in rare circumstances. The sudden attacks of pain typically last only seconds to minutes; however, they may be repeated one after the other, and can be brought on by such triggers as talking, brushing the teeth, touching the face, chewing, drinking, swallowing, kissing, or even a gentle breeze. The attacks may come and go throughout the day and can last for days or months at a time, and then disappear for months or years.

Trigeminal neuralgia is among the most intensely painful afflictions known to man, and the fear of the pain alone may virtually incapacitate the patient. TN is not fatal, but even during periods of remission, sufferers live in fear of the next flare-up of pain. As time goes by, the attacks tend to become more severe and more frequent, and the periods of remission become shorter. The need for aggressive intervention therefore increases as the disease invariably progresses.

Because sufferers of TN may contort their face in pain or become noticeably still during an attack, the disease has sometimes been confused with a seizure disorder, hence the term “tic douloureux” which means “twitching pain.”

Cause of trigeminal neuralgia
The exact cause of trigeminal neuralgia is controversial, but it is suggested that an area of vascular compression where the trigeminal nerve enters the brain may be the culprit. This compression may cause damage to the myelin sheath (the insulating cover of a nerve fiber) that surrounds the trigeminal nerve. Other precipitating factors include multiple sclerosis and hypertension.

The incidence of TN in the United States is approximately 4-5 per 100,000 people. There does not seem to be any association with race, but women are more likely to develop the disease than men, at a ratio of 3:2. The age of onset is typically 60-70 years; those who are diagnosed between ages 20 and 40 are more likely to suffer from multiple sclerosis as a precipitating cause. Prevalence in those diagnosed after age 70 increases to as many as 25 per 100,000 people over 70 years old.

Clinical manifestations
Trigeminal neuralgia pain is almost always one-sided, and affects the right side of the face nearly five times more often than the left. The pain is described as severe and shock-like, increasing in intensity to an excruciating discomfort felt deep in the face. The pain then begins to fade, but may result in a burning ache that lasts for several more minutes. TN attacks may occur less than once a day up to hundreds of times per day. In between attacks, the patient is generally pain-free.

TN pain often shoots from the corner of the mouth to the angle of the jaw, from the upper lip or teeth to the eye and eyebrow, or any other portion of the jaw or face. After the initial attack, the pain may disappear for months or years.

In contrast to pain associated with migraine headaches, patients with TN rarely suffer attacks of pain during sleep. In addition, the pain is generally not associated with facial weakness, swallowing difficulties, or pain in the orbits of the eyes. These symptoms suggest something other than trigeminal neuralgia.

Neurological examination in trigeminal neuralgia patients is typically normal. In fact, if it is not normal, the patient probably has something other than trigeminal neuralgia or may have something in addition to TN (such as multiple sclerosis or a tumor).

Since no structural lesion is present in trigeminal neuralgia, brain MRI with and without contrast appears normal. This imaging study helps to distinguish TN from other causes of the pain. No other specific diagnostic testing is generally indicated, as most will elicit normal results. A patient’s description of the pain and a therapeutic trial of medications are generally the most reliable methods to confirm TN. Many TN sufferers endure years of misdirected treatments before the disease is recognized. The most common incorrect diagnoses include dental disorders, sinus infections, temporal arteritis, migraine headaches, and psychological disorders. These errors frequently result in unnecessary tooth extractions, root canals, sinus surgeries, biopsies, and antibiotic utilization.

Medical management of trigeminal neuralgia is often sufficient and effective, and surgical or radiosurgical therapy is generally only considered after treatment with medications has failed. The most common medication prescribed for TN is carbamazepine (Tegretol). Other patients are treated with anticonvulsants such as phenytoin (Dilantin), gabapentin (Neurontin), or lamotrigine (Lamictal). These medications work by interrupting the nerve impulses that trigger the painful attacks.

Treatment with carbamazepine is generally so effective and so quick (often produces complete relief of pain within two hours) that it is considered the drug of choice for trigeminal neuralgia. Additionally, it is the drug most often used on a trial basis to help confirm the diagnosis of TN. Another drug that is used to help relieve TN pain is Baclofen (or Lioresal) which works as a muscle relaxant to help relieve spasms and cramping. Once a patient achieves pain relief with a single medication, a second or third medication is often added to sustain relief.

Occasionally, the medications used for trigeminal neuralgia pain lose effectiveness, and patients must resort to surgery for relief of their pain. According to some reports, as many as 25 – 50 % of patients require some alternative form of treatment other than medication. For patients who are diagnosed before age 60, surgery (either microsurgery or Gamma Knife) is considered the definitive treatment for TN. Surgery exposes the patient to some significant risks, however, and these must be taken into consideration when considering the treatment plan for trigeminal pain.

Surgical treatment of trigeminal neuralgia pain
There are two main types of surgical intervention in trigeminal neuralgia: percutaneous (meaning that the procedure is performed through the skin) procedures and microvascular decompression. Percutaneous procedures include percutaneous radiofrequency trigeminal rhizotomy, percutaneous retrogasserian glycerol rhizotomy, and percutaneous balloon microcompression. In each of these procedures, the nerve cells are destroyed utilizing heat, glycerol, or an inflated balloon catheter. The procedures are performed on an outpatient basis with minimal risks.

Microvascular decompression is an invasive procedure in which the trigeminal nerve is exposed by opening the skull, and the arterial vessel that is compressing the nerve is padded. The surgery involves several days in the hospital and is not without risk of infection, stroke, and hearing loss. These incidents occur in 1-5% of cases.

Most patients achieve pain relief after any of these treatment options. Some reports say that as many as 90% of patients undergoing one of the treatments above are pain free after their operations. The percutaneous procedures generally provide pain relief for 1.5 – 4 years. Microvascular decompression can provide as much as 15 years of pain relief. However, some patients require pain medication even after surgery, and some have complications that can be worse than the original TN, such as anesthesia dolorosa (a complication which occurs when the trigeminal nerve is damaged by surgery or physical trauma in such a way that the feeling sensation in part of the face is reduced or eliminated entirely while the sense of pain remains). For this reason, procedures with the best long-term success and least risk of irreversible complications should be chosen.

Gamma Knife radiosurgery
In 1951, the Swedish neurosurgeon Lars Leksell presented the idea of converging a large number of beams of ionizing radiation to crossfire at one target in the brain. He coined the term “radiosurgery” to describe this concept, because the technique differed greatly from conventional radiotherapy. He suggested radiosurgery for the treatment of deep-seated brain tumors and functional disorders. The first device for routine clinical use based on this idea was the prototype Gamma Knife constructed in 1967. However, Dr. Leksell’s first radiosurgical procedure in 1951 was undertaken for the treatment of trigeminal neuralgia.
Stereotactic radiation therapy, referred to as “radiosurgery” or “radiotherapy,” is a technique based on the principle that radiation delivered precisely to a target will destroy the cells in a particular area while minimizing injury to surrounding nerves and brain tissue. During the Gamma Knife procedure, 201 small beams of radiation are aimed at the target area or lesion. This results in a high dose of radiation to the target and very little radiation to the surrounding brain structures. Radiosurgery is delivered as a one-time, outpatient treatment. Many patients have been treated this way with high success rates. Side effects or complications are almost non-existent or minimal at worst.

Obvious advantages of radiosurgery are its non-invasive nature, its shortened immediate recovery time, its preservation of normal brain tissue, and its value as an alternative for patients unable or unwilling to undergo surgery. On the other hand, radiosurgery is limited to small or medium tumors or target areas. Because trigeminal neuralgia can be treated by irradiating an area well within these size limitations, Gamma Knife is a reasonable and effective choice of treatment for this disorder.

The source of radiation used in radiosurgery with the Gamma Knife is radioactive cobalt. The radiation is called a gamma ray when it comes from a cobalt source. The treatment team consists of a neurosurgeon, a radiation oncologist, a medical physicist, and a nurse. The physicians and physicists work together to develop a treatment plan based on the size and shape of the target area or tumor.

In radiosurgery patients, nerve changes are not immediate. In a multi-institutional study reported in the June 1996 Journal of Neurosurgery, 50 patients were studied following Gamma Knife treatment for trigeminal neuralgia. Pain relief was achieved in these patients in a range from one day to 6.7 months, with a mean of one month. Of these patients, 58% experienced excellent results (meaning 100% pain relief), 36% experienced good results (meaning 50-90% improvement), and only 6% experienced poor results (meaning 0-50% improvement). These results remained consistent at three years of follow-up study. None of the patients developed other deficits. A study of 106 patients performed at the University of Pittsburgh in 1997 showed an approximate 80% rate of significant pain relief and a low recurrence rate in patients who initially achieved complete relief of pain.

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