Trigeminal neuralgia

Trigeminal neuralgia (TN), or Tic Douloureux, ( also known as prosopalgia ) is a neuropathic disorder of the trigeminal nerve that causes episodes of intense pain in the eyes, lips, nose, scalp, forehead, and jaw.^[1] Trigeminal neuralgia is considered by many to be among the most painful of conditions and once was labeled the "suicide disease" because of the significant numbers of people taking their own lives before effective treatments were discovered. An estimated one in 15,000 people suffers from trigeminal neuralgia, although numbers may be significantly higher due to frequent misdiagnosis. It usually develops after the age of 40, although there have been cases with patients being as young as three years of age ^[2].

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Pathophysiology

The pain of trigeminal neuralgia is often falsely attributed to a pathology of dental origin. "Rarely do patients come to the surgeon without having had removed many, and not infrequently all, teeth on the affected side or both sides." ^[3] Extractions do not help for the pain is originating in the trigeminal nerve and not in an individual nerve of a tooth. Because of this difficulty, many patients may go untreated for long periods of time before a correct diagnosis is made. The trigeminal nerve is the fifth cranial nerve, a mixed cranial nerve responsible for sensory data such as tactition (pressure), thermoception (temperature), and nociception (pain) originating from the face above the jawline; it is also responsible for the motor function of the muscles of mastication, the muscles involved in chewing but not facial expression. Several theories exist to explain the possible causes of this pain syndrome. The leading explanation is that a blood vessel is likely to be compressing the trigeminal nerve near its connection with the pons. The superior cerebellar artery is the most-cited culprit. Such a compression can injure the nerve's protective myelin sheath and cause erratic and hyperactive functioning of the nerve. This can lead to pain attacks at the slightest stimulation of any area served by the nerve as well as hinder the nerve's ability to shut off the pain signals after the stimulation ends. This type of injury also may be caused by an aneurysm (an outpouching of a blood vessel); by a tumor; by an arachnoid cyst in the cerebellopontine angle^[4], or by a traumatic event such as a car accident or even a tongue piercing. [1] Two to four percent of patients with TN, usually younger, have evidence of multiple sclerosis, which may damage either the trigeminal nerve or other related parts of the brain. When there is no structural cause, the syndrome is called idiopathic. Postherpetic Neuralgia, which occurs after shingles, may cause similar symptoms if the trigeminal nerve is affected.

Symptoms

The episodes of pain occur paroxysmally, or suddenly. To describe the pain sensation, patients describe a trigger area on the face, so sensitive that touching or even air currents can trigger an episode of pain. It affects lifestyle as it can be triggered by common activities in a patient's daily life, such as toothbrushing. Breezes, whether cold or warm, wintry weather or even light touching such as a kiss can set off an attack. The attacks are said to feel like stabbing electric shocks or shooting pain that becomes intractable. Individual attacks affect one side of the face at a time, last several seconds or longer, and repeats up to hundreds of times throughout the day. The pain also tends to occur in cycles with complete remissions lasting months or even years. 3-5% of cases are bilateral, or occurring on both sides. This normally indicates problems with both trigeminal nerves since one serves strictly the left side of the face and the other serves the right side. Pain attacks typically worsen in frequency or severity over time. A great deal of patients develop the pain in one branch, then over years the pain will travel through the other nerve branches.

Signs of this can be seen in males who may deliberately miss an area of their face when shaving, in order to avoid triggering an episode. Although trigeminal neuralgia is not fatal, successive recurrences may be incapacitating, and the fear of provoking an attack may make sufferers reluctant to engage in normal activities.

There is a variant of trigeminal neuralgia called "atypical trigeminal neuralgia". In some cases of atypical trigeminal neuralgia, the sufferer experiences a severe, relentless underlying pain similar to a migraine in addition to the stabbing pains. This variant is sometimes called "trigeminal neuralgia, type 2"[2], based on a recent classification of facial pain^[5]. In other cases, the pain is stabbing and intense, but may feel like burning or prickling, rather than a shock. Sometimes, the pain is a combination of shock-like sensations, migraine-like pain, and burning or prickling pain. It can also feel as if a boring piercing pain is unrelenting.

Treatment

There is no cure for trigeminal neuralgia, but most people find relief from medication, from one of the five surgical options or sometimes from one of the many so-called "complementary or alternative" therapies. Atypical trigeminal neuralgia, which involves a more constant and burning pain, is more difficult to treat, both with medications and surgery. Surgery may result in varying degrees of numbness to the patient and lead occasionally to "anesthesia dolorosa," which is numbness with intense pain. However, many people do find dramatic relief with minimal side effects from the various surgeries that are now available.^[6] During a TN attack, some patients may get quick relief by applying an ice pack or a readily available source of cold temperature to the area of pain.^{[citation needed]}

Medications

• Anticonvulsants such as carbamazepine, oxcarbazepine, topiramate, phenytoin, or gabapentin are generally the most effective medications. Pain relievers usually do not help. Anticonvulsant effects may be potentiated with an adjuvant such as baclofen or clonazepam. Baclofen may also help some patients eat more normally if jaw movement tends to aggravate the symptoms.

• If anticonvulsants don't help and surgical options have failed or are ruled out, the pain may be treated long-term with an opioid such as methadone.

• Low doses of some antidepressants can be effective in treating neuropathic pain.

• Botox can be injected into the nerve by a physician, and has been found helpful using the "migraine" pattern adapted to the patient's special needs.

Many patients cannot tolerate medications for years, and an alternate treatment is to take a drug such as gabapentin and place it in an externally applied cream base by a pharmacist who compounds drugs. Also helpful is taking a "drug holiday" when remissions occur and rotating medications if one becomes ineffective.

Surgery

Surgery may be recommended, either to relieve the pressure on the nerve or to selectively damage it in such a way as to disrupt pain signals from getting through to the brain. In trained hands, surgical success rates have been reported at better than 90 percent.

Of the five surgical options, the microvascular decompression is the only one aimed at fixing the presumed cause of the pain. In this procedure, the surgeon enters the skull through a 25mm (one-inch) hole behind the ear. The nerve is then explored for an offending blood vessel, and when one is found, the vessel and nerve are separated or "decompressed" with a small pad. When successful, MVD procedures can give permanent pain relief with little to no facial numbness.

Three other procedures use needles or catheters that enter through the face into the opening where the nerve first splits into its three divisions. Excellent success rates using a cost effective percutaneous surgical procedure known as balloon compression have been reported^[7]. This technique has been helpful in treating the elderly for whom surgery may not be an option due to coexisting health conditions. Balloon compression is also the best choice for patients who have ophthalmic nerve pain or have experienced recurrent pain after microvascular decompression.

Similar success rates have been reported with glycerol injections and radiofrequency rhizotomies. Glycerol injections involve injecting an alcohol-like substance into the cavern that bathes the nerve near its junction. This liquid is corrosive to the nerve fibers and can mildly injure the nerve enough to hinder the errant pain signals. In a radiofrequency rhizotomy, the surgeon uses an electrode to heat the selected division or divisions of the nerve. Done well, this procedure can target the exact regions of the errant pain triggers and disable them with minimal numbness.

Stereotactic Radiation Therapy

The nerve can also be damaged to prevent pain signal transmission using Gamma Knife or a linear accelerator-based radiation therapy (e.g. Novalis, Cyberknife). No incisions are involved in this procedure. It uses radiation to bombard the nerve root, this time targeting the selective damage at the same point where vessel compressions are often found. This option is used especially for those people who are medically unfit for a long general anaesthetic, or who are taking medications for prevention of blood clotting (e.g., warfarin). A prospective Phase I trial performed at Marseille, France, showed that 83% of patients were pain-free at 12 months, with 58% pain-free and off all medications. Side effects were mild, with 6% experiencing mild tingling and 4% experiencing mild numbness.^[8]

Other

Alternative and complementary health care treatments such as chiropractic or acupuncture are sometimes used either in combination with drugs or alone to help manage pain. Other treatments include capsaicin cream, B-12 supplements, dietary modification or covering the face to avoid wind and other mild sensory triggers.

In one case of trigeminal neuralgia associated with tongue-piercing, the condition resolved after the jewelry was removed.^[9]

References