Trigeminal neuralgia is a rare disorder of the sensory fibers of the trigeminal nerve (fifth cranial nerve), which innervate the face and jaw. The neuralgia is accompanied by severe, stabbing pains in the jaw or face, usually on one side of the jaw or cheek, which usually last for some seconds. The pain before treatment is severe; however, trigeminal neuralgia as such is not a life-threatening condition. As there are actually two trigeminal nerves, one for each side of the face, trigeminal neuralgia often affects only one side of the face, depending on which of the two trigeminal nerves is affected.
There have been no systematic studies of the prevalence of trigeminal neuralgia, but one widely quoted estimate published in 1968 states that its prevalence is approximately 15.5 per 100,000 persons in the United States. Other sources state that the annual incidence is four to five per 100,000 persons, which would imply a higher prevalence (prevalence is the number of cases in a population at a given time; incidence is the number of new cases per year). In any case, the disorder is rare. Onset is after the age of 40 in 90% of patients. Trigeminal neuralgia is slightly more common among women than men.
Causes and symptoms
A number of theories have been advanced to explain trigeminal neuralgia, but none explains all the features of the disorder. The trigeminal nerve is made up of a set of branches radiating from a bulblike ganglion (nerve center) just above the joint of the jaw. These branches divide and subdivide to innervate the jaw, nose, cheek, eye, and forehead. Sensation is conveyed from the surfaces of these parts to the upper spinal cord and then to the brain; motor commands are conveyed along parallel fibers from the brain to the muscles of the jaw. The sensory fibers of the trigeminal nerve are specialized for the conveyance of cutaneous (skin) sensation, including pain.
In trigeminal neuralgia, the pain-conducting fibers of the trigeminal nerve are somehow stimulated, perhaps self-stimulated, to send a flood of impulses to the brain. Many physicians assume that compression of the trigeminal nerve near the spinal cord by an enlarged loop of the carotid artery or a nearby vein triggers this flood of impulses. Compression is thought to cause trigeminal neuralgia when it occurs at the root entry zone, a. 19–.39 in (0.5–1.0 cm) length of nerve where the type of myelination changes over from peripheral to central. Pressure on this area may cause demyelination, which in turn may cause abnormal, spontaneous electrical impulses (pain).
Compression is apparently the cause in some cases of trigeminal neuralgia, but not in others. Other theories focus on complex feedback mechanisms involving the subnucleus caudalis in the brain. Multiple sclerosis, which demyelinates nerve fibers, is associated with a higher rate of trigeminal neuralgia. Brain tumors can also be correlated with the occurrence of trigeminal neuralgia. Ultimately, however, the exact mechanisms of trigeminal neuralgia remain a mystery.
Trigeminal neuralgia was first described by the Arab physician Jurjani in the eleventh century. Jurjani was also
The pains of trigeminal neuralgia have several distinct characteristics, including:
- They are paroxysmal, pains that start and end suddenly, with painless intervals between.
- They are usually extremely intense.
- They are restricted to areas innervated by the trigeminal nerve.
- As seen on autopsy, nothing is visibly wrong with the trigeminal nerve.
- About 50% of patients have trigger zones, areas where slight stimulation or irritation can bring on an episode of pain. Painful stimulation of the trigger zones is actually less effective than light stimulation in triggering an attack.
- The disorder comes and goes in an unpredictable way; some patients show a correlation of attack frequency or severity with stress or menstrual cycle.
Stimulation of the face, lips, or gums, such as talking, eating, shaving, tooth-brushing, touch, or even a current of air, may trigger the severe knifelike or shocklike pain of trigeminal neuralgia, often described as excruciating. Trigger zones may be a few square millimeters in size, or large and diffuse. The pain usually starts in the trigger zone, but may start elsewhere. Approximately 17% of patients experience dull, aching pain for days to years before the onset of paroxysmal pain; this has been termed pretrigeminal neuralgia.
The pain of trigeminal neuralgia is severe enough that patients often modify their behaviors to avoid it. They may suffer severe weight loss from inability to eat, become unwilling to talk or smile, and cease to practice oral hygiene. Trigeminal neuralgia tends to worsen with time, so that a patient whose pain is initially well-controlled with medication may eventually require surgery.
Trigeminal neuralgia is a possible diagnosis for any patient presenting with severe, stabbing, paroxysmal pain in the jaw or face. However, the most common causes of facial pain are dental problems and diseases of the mouth. Trigeminal neuralgia must also be differentiated from migraine headaches and from other cranial neuralgias (i.e., neuralgias affecting cranial nerves other than the trigeminal). Many persons with trigeminal neuralgia see multiple physicians before getting a correct diagnosis, and may have multiple dental procedures performed in an effort to relieve the pain.
There is no definitive, single test for trigeminal neuralgia. Imaging studies such as computed tomography (CT) scans or magnetic resonance imaging (MRI) may help to rule out other possible causes of pain and to indicate trigeminal neuralgia. High-definition MRI angiography of the trigeminal nerve and brain stem is often able to spot compression of the trigeminal nerve by an artery or vein. Trial and error also has its place in the diagnostic process; the physician may initially give the patient carbamazepine (an anticonvulsant) to see if this diminishes the pain. If so, this is positive evidence for the diagnosis of trigeminal neuralgia.
Many different sorts of health care professionals may be consulted by patients with trigeminal neuralgia, including dentists, neurologists, neurosurgeons, oral surgeons, and ear, nose, and throat surgeons. A referral to a neurologist should always be sought, as trigeminal neuralgia is essentially a neurological problem.
Treatment is primarily with drugs or surgery. Drugs are often preferred because of their lower risk, but may have intolerable side effects such as nausea or ataxia (loss of muscle coordination). The two most effective drugs are carbamazepine (an anticonvulsant often used in treating epilepsy), used for trigeminal neuralgia since 1962, and gabapentin. Drugs are prescribed initially in low doses and increased until an effective level is found. Other drugs in use for trigeminal neuralgia are phenytoin, baclofen, clonazepam, lamotrigine topiramate, and trileptal.
Carbamazepine, which inhibits the activity of sodium channels in the cell membranes of neurons (thereby reducing their excitability), is deemed the most effective medication for trigeminal neuralgia. Unfortunately, it has many side effects, including vertigo (dizziness), ataxia, and sedation (mental dullness). This may make it harder to treat elderly patients, who are more likely to have trigeminal neuralgia. Carbamazepine provides complete or partial relief for as many as 70% of patients. Phenytoin is also a sodium channel blocker, and also has adverse side effects, including hirsutism (increased facial hair), coarsening of facial features, and ataxia.
For patients whose pain does not respond adequately to medication, or who cannot tolerate the medication itself due to side effects, surgery is considered. Approximately 50% of trigeminal neuralgia patients eventually undergo surgery of some kind for their condition. The most common procedure is microvascular decompression, also known as the Jannetta procedure after its inventor. This involves surgery to separate the vein or artery compressing the trigeminal nerve. Teflon or polivinyl alcohol foam is inserted to cushion the trigeminal nerve against the vein or artery. This procedure is often effective, but some physicians argue that since other procedures that disturb or injure the trigeminal nerve are also effective, the benefit of microvascular decompression surgery is not relief of compression but disturbance of the trigeminal nerve, causing nonspecific nerve injury that leads to a change in neural activity.
Other surgical procedures are performed, some of which focus on destroying the pain-carrying fibers of the trigeminal nerve. The most high-tech and least invasive procedure is gamma-ray knife surgery, which uses approximately 200 convergent beams of gamma rays to deliver a high (and highly localized) radiation dose to the trigeminal nerve root. Almost 80% of patients undergoing this procedure experience significant relief with this procedure, although about 10% develop facial paresthesias (odd, non-painful sensations not triggered by any external stimulus).
As of mid-2004, one clinical trial related to trigeminal neuralgia was recruiting patients. This study, titled "Randomized Study of L-Baclofen in Patients with Refractory Trigeminal Neuralgia," was being carried out at the University of Pennsylvania, Pittsburgh, and was sponsored by the FDA Office of Orphan Products Development (dedicated to promoting the development of treatments for diseases too rare to be considered profitable by pharmaceutical companies). Its goal is to test the effectiveness and safety of the drug L-baclofen in patients with refractory (treatment-resistant) trigeminal neuralgia. The contact is Michael J. Soso at the University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, 15261, telephone (412) 648-1239. Forms of baclofen have been used for the treatment of trigeminal neuralgia since 1980.
Trigeminal neuralgia is not life threatening. It tends, however, to worsen with time, and many patients who initially were successfully treated with medication must eventually resort to surgery. Some doctors advocate surgery such as microvascular decompression early in the course of the syndrome to forestall the demyelination damage. However, there is still much controversy and uncertainty about the causes of trigeminal neuralgia and the mechanism of benefit even in those treatments that provide relief for many patients.
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Trigeminal Neuralgia Association. 2801 SW Archer Road, Gainesville, FL 32608. (352) 376-9955; Fax: (352) 376-8688. firstname.lastname@example.org. <http://www.tnasupport.org/>.