HEADACHE AND FACIAL PAIN: TRIGEMINAL NEURALGIA

Trigeminal neuralgia (TN), also called tic douloureux, is a chronic pain condition that affects the trigeminal or fifth cranial nerve, one of the largest nerves in the head. The disorder causes extreme, sporadic, sudden burning or shock-like face pain that lasts anywhere from a few seconds to as long as two minutes per episode. The intensity of pain can be physically and mentally incapacitating.

The trigeminal nerve is one of 12 pairs of cranial nerves that originate at the base of the brain. The nerve has three branches that conduct sensations from the upper, middle and lower portions of the face, as well as the oral cavity, to the brain. The ophthalmic, or upper, branch supplies sensation to most of the scalp, forehead and front of the head. The maxillary, or middle, branch passes through the cheek, upper jaw, top lip, teeth and gums, and to the side of the nose. The nerve’s mandibular, or lower, branch passes through the lower jaw, teeth, gums and bottom lip. More than one nerve branch can be affected by the disorder.

The presumed cause of TN is a blood vessel pressing on the trigeminal nerve as it exits the brainstem. This compression causes the wearing away of the protective coating around the nerve (the myelin sheath). TN may be part of the normal aging process — as blood vessels lengthen they can come to rest and pulsate against a nerve. TN symptoms also can occur in people with multiple sclerosis, a disease caused by the deterioration of myelin throughout the body, or may be caused by damage to the myelin sheath by compression from a tumor. This deterioration causes the nerve to send abnormal signals to the brain. In some cases the cause is unknown.

TN is characterized by a sudden, severe, electric shock-like, stabbing pain that is typically felt on one side of the jaw or cheek. Pain may occur on both sides of the face, although not at the same time. The attacks of pain, which generally last several seconds and may repeat in quick succession, come and go throughout the day. These episodes can last for days, weeks or months at a time and then disappear for months or years. In the days before an episode begins, some patients may experience a tingling or numbing sensation or a somewhat constant and aching pain.

The intense flashes of pain can be triggered by vibration or contact with the cheek (such as when shaving, washing the face or applying makeup), brushing teeth, eating, drinking, talking or being exposed to the wind. The pain may affect a small area of the face or may spread. The bouts of pain rarely occur at night, when the patient is sleeping.

Patients are considered to have Type 1 TN if more than 50 percent of the pain they experience is sudden, intermittent, sharp and stabbing or shock-like. These patients may also have some burning sensation. Type 2 TN involves pain that is constant, aching or burning more than 50 percent of the time.

TN is typified by attacks that stop for a period of time and then come back. The attacks often worsen over time, with fewer and shorter pain-free periods before they recur. The disorder is not fatal, but can be debilitating. Due to the intensity of the pain, some patients may avoid daily activities because they fear an impending attack.

TN occurs most often in people older than age 50, but it can occur at any age. The disorder is more common in women than in men. There is some evidence that the disorder runs in families, perhaps because of an inherited pattern of blood vessel formation.

There is no single test to diagnose TN. Diagnosis is generally based on the patient’s medical history and description of symptoms, a physical exam and a thorough neurological examination by a physician. Other disorders, such as post-herpetic neuralgia, can cause similar facial pain, as do syndromes such as cluster headaches. Injury to the trigeminal nerve (perhaps the result of sinus surgery, oral surgery, stroke or facial trauma) may produce neuropathic pain, which is characterized by dull, burning and boring pain. Because of overlapping symptoms, and the large number of conditions that can cause facial pain, obtaining a correct diagnosis is difficult, but finding the cause of the pain is important as the treatments for different types of pain may differ.

Most TN patients undergo a standard magnetic resonance imaging scan to rule out a tumor or multiple sclerosis as the cause of their pain. This scan may or may not clearly show a blood vessel on the nerve. Magnetic resonance angiography, which can trace a colored dye that is injected into the bloodstream prior to the scan, can more clearly show blood vessel problems and any compression of the trigeminal nerve close to the brainstem.

Treatment options include medicines, surgery and complementary approaches.

Anticonvulsant Medicines
Anticonvulsant medicines — used to block nerve firing — are generally effective in treating TN. These drugs include carbamazepine, oxcarbazepine, topiramate, clonazepam, phenytoin, lamotrigin and valproic acid. Gabapentin or baclofen can be used as a second drug to treat TN and may be given in combination with other anticonvulsants.

Tricyclic Antidepressants
Tricyclic antidepressants, such as amitriptyline or nortriptyline, are used to treat pain described as constant, burning or aching. Typical analgesics and opioids are not usually helpful in treating the sharp, recurring pain caused by TN. If medication fails to relieve pain or produces intolerable side effects such as excess fatigue, surgical treatment may be recommended.

Neurosurgical Procedures
Several neurosurgical procedures are available to treat TN. The choice among the various types depends on the patient's preference, physical well-being, previous surgeries, presence of multiple sclerosis and area of trigeminal nerve involvement (particularly when the upper/ophthalmic branch is involved). Some procedures are done on an outpatient basis, while others may involve a more complex operation that is performed under general anesthesia. Some degree of facial numbness is expected after most of these procedures, and TN might return despite the procedure’s initial success. Depending on the procedure, other surgical risks include hearing loss, balance problems, infection and stroke.

A rhizotomy is a procedure in which select nerve fibers are destroyed to block pain. A rhizotomy for TN causes some degree of permanent sensory loss and facial numbness. Several forms of rhizotomy are available to treat TN:

· Balloon Compression. Balloon compression works by injuring the insulation on nerves that are involved with the sensation of light touch on the face. The procedure is performed in an operating room under general anesthesia. A tube called a cannula is inserted through the cheek and guided to where one branch of the trigeminal nerve passes through the base of the skull. A soft catheter with a balloon tip is threaded through the cannula and the balloon is inflated to squeeze part of the nerve against the hard edge of the brain covering (the dura) and the skull. After one minute the balloon is deflated and removed, along with the catheter and cannula. Balloon compression is generally an outpatient procedure, although sometimes the patient may be kept in the hospital overnight.

· Glycerol Injection. Glycerol injection is generally an outpatient procedure in which the patient is sedated intravenously. A thin needle is passed through the cheek, next to the mouth and guided through the opening in the base of the skull to where all three branches of the trigeminal nerve come together. The glycerol injection bathes the ganglion (the central part of the nerve from which the nerve impulses are transmitted) and damages the insulation of trigeminal nerve fibers.

· Radiofrequency Thermal Lesioning. Radiofrequency thermal lesioning is usually performed on an outpatient basis. The patient is anesthetized and a hollow needle is passed through the cheek to where the trigeminal nerve exits through a hole at the base of the skull. The patient is awakened and a small electrical current is passed through the needle, causing tingling. When the needle is positioned so that the tingling occurs in the area of TN pain, the patient is then sedated and that part of the nerve is gradually heated with an electrode, injuring the nerve fibers. The electrode and needle are then removed and the patient is awakened.

· Stereotactic Radiosurgery. Stereotactic radiosurgery uses computer imaging to direct highly focused beams of radiation at the site where the trigeminal nerve exits the brainstem. This causes the slow formation of a lesion on the nerve that disrupts the transmission of pain signals to the brain. Pain relief from this procedure may take several months. Patients usually leave the hospital the same day or the next day following treatment.

· Microvascular Decompression. Microvascular decompression is the most invasive of all surgeries for TN, but it also offers the lowest probability that pain will return. This inpatient procedure, which is performed under general anesthesia, requires that a small opening be made behind the ear. While viewing the trigeminal nerve through a microscope, the surgeon moves away the vessels that are compressing the nerve and places a soft cushion between the nerve and the vessels. Unlike rhizotomies, there is usually no numbness in the face after this surgery. Patients generally recuperate for several days in the hospital following the procedure. A neurectomy, which involves cutting part of the nerve, may be performed during microvascular decompression if no vessel is found to be pressing on the trigeminal nerve. Neurectomies may also be performed by cutting branches of the trigeminal nerve in the face. When done during microvascular decompression, a neurectomy will cause permanent numbness in the area of the face that is supplied by the nerve or nerve branch that is cut. However, when the operation is performed in the face, the nerve may grow back and in time sensation may return.

Some patients choose to manage TN using complementary techniques, usually in combination with drug treatment. These therapies offer varying degrees of success. Options include acupuncture, biofeedback, vitamin therapy, nutritional therapy and electrical stimulation of the nerves.

The National Institute of Neurological Disorders and Stroke (NINDS), a part of the National Institutes of Health, is the federal government’s leading supporter of biomedical research on disorders of the brain and nervous system. One NINDS-funded study is examining the neurophysiological characteristics of TN to see if the disorder is associated with abnormal sensory input from the peripheral nervous system. Observations from this study should allow scientists to better understand the nerve cell mechanisms of TN, develop better animal models of the disorder and find better medical and surgical treatments for TN and other nerve pain disorders. Other NINDS-funded projects address TN through studies associated with pain research.

Some NIH-funded research examines functional and chemical changes in sensory neurons in the peripheral and central nervous systems, and evaluates the roles of nerve growth factor and sympathetic nerves in the development of neuropathic pain.