Trigeminal Neuralgia 

Trigeminal neuralgia (TN), also known as tic douloureux, is a common and potentially disabling pain syndrome, the precise pathophysiology of which remains obscure. This condition has been known to drive patients with trigeminal neuralgia to the brink of suicide. Although neurologic examination findings are normal in patients with the idiopathic variety, the most common type of facial pain neuralgia, the clinical history is distinctive. Trigeminal neuralgia is characterized by unilateral pain following the sensory distribution of cranial nerve V—typically radiating to the maxillary (V2) or mandibular (V3) area in 35% of affected patients (see the image below)—often accompanied by a brief facial spasm or tic. Isolated involvement of the ophthalmic division is much less common (2.8%).

Typically, the initial response to carbamazepine therapy is diagnostic and successful. Despite obtaining this satisfying early relief with medication, patients may experience breakthrough pain that requires additional drugs and, in some patients, one or more of a variety of surgical interventions.

Historical information

The clinical description of trigeminal neuralgia can be traced back more than 300 years. Aretaeus of Cappadocia, known for one of the earliest descriptions of migraine, is credited with the first indication of trigeminal neuralgia when e described a headache in which "spasms and distortions of the countenance took place." Nicholaus Andre coined the term tic douloureux in 1756.

John Fothergill was the first to give a full and accurate description of this condition in a paper titled "On a Painful Affliction of the Face," which he presented to the medical society of London in 1773. Osler also described trigeminal neuralgia in great and accurate detail in his 1912 book The Principles and Practice of Medicine.^[1]

In 1900, in a landmark article, Cushing reported a method of total ablation of the gasserian ganglion to treat trigeminal neuralgia.

See also Trigeminal Neuralgia Surgery.

The trigeminal nerve is the largest of all the cranial nerves. It exits laterally at the mid-pons level and has 2 divisions—a smaller motor root (portion minor) and a larger sensory root (portion major). The motor root supplies the temporalis, pterygoid, tensor tympani, tensor palati, mylohyoid, and anterior belly of the digastric. The motor root also contains sensory nerve fibers that particularly mediate pain sensation.

The gasserian ganglion is located in the trigeminal fossa (Meckel cave) of the petrous bone in the middle cranial fossa. It contains the first-order general somatic sensory fibers that carry pain, temperature, and touch. The peripheral processes of neurons in the ganglion form the 3 divisions of the trigeminal nerve (ie, ophthalmic, maxillary, and mandibular). The ophthalmic division exits the cranium via the superior orbital fissure; the maxillary and mandibular divisions exit via the foramen rotundum and foramen ovale, respectively.

The proprioceptive afferent fibers travel with the efferent and afferent roots. They are peripheral processes of unipolar neurons located centrally in the mesencephalic nucleus of the trigeminal nerve.

The image below depicts the anatomy of the trigeminal nerve.

Because the exact pathophysiology remains controversial, the etiology of trigeminal neuralgia (TN) may be central, peripheral, or both. The trigeminal nerve (cranial nerve V) can cause pain, because its major function is sensory. Usually, no structural lesion is present (85%), although many investigators agree that vascular compression, typically venous or arterial loops at the trigeminal nerve entry into the pons, is critical to the pathogenesis of the idiopathic variety. This compression results in focal trigeminal nerve demyelination. The etiology is labeled idiopathic by default and is then categorized as classic trigeminal neuralgia.

Neuropathic pain is the cardinal sign of injury to the small unmyelinated and thinly myelinated primary afferent fibers that subserve nociception. The pain mechanisms themselves are altered. Microanatomic small and large fiber damage in the nerve, essentially demyelination,^[2] commonly observed at its root entry zone (REZ), leads to ephaptic transmission, in which action potentials jump from one fiber to another.^[3] A lack of inhibitory inputs from large myelinated nerve fibers plays a role. Additionally, a reentry mechanism causes an amplification of sensory inputs. A clinical correlate, for instance, is the potential for vibration to trigger an attack. However, features also suggest an additional central mechanism (eg, delay between stimulation and pain, refractory period).

Although a questionable family clustering exists, trigeminal neuralgia (TN) is most likely is multifactorial.

Most cases of trigeminal neuralgia are idiopathic, but compression of the trigeminal roots by tumors or vascular anomalies may cause similar pain, as discussed in Pathophysiology. In one study, 64% of the compressing vessels were identified as an artery, most commonly the superior cerebellar (81%).^[4] Venous compression was identified in 36% of cases.^[4]

Trigeminal neuralgia is divided into 2 categories, classic and symptomatic. The classic form, considered idiopathic, actually includes the cases that are due to a normal artery present in contact with the nerve, such as the superior cerebellar artery or even a primitive trigeminal artery.

Symptomatic forms can have multiple origins. Aneurysms, tumors, chronic meningeal inflammation, or other lesions may irritate trigeminal nerve roots along the pons causing symptomatic trigeminal neuralgia. An abnormal vascular course of the superior cerebellar artery is often cited as the cause. Uncommonly, an area of demyelination from multiple sclerosis may be the precipitant (see the following image); lesions in the pons at the root entry zone of the trigeminal fibers have been demonstrated. These lesions may cause a similar pain syndrome as in trigeminal neuralgia.

Tumor-related causes of trigeminal neuralgia (most commonly in the cerebello-pontine angle) include acoustic neurinoma, chordoma at the level of the clivus, pontine glioma or glioblastoma,^[5] epidermoid, metastases, and lymphoma. Trigeminal neuralgia may result from paraneoplastic etiologies.

Vascular causes include a pontine infarct and arteriovenous malformation or aneurysm in the vicinity.

Inflammatory causes include multiple sclerosis (common), sarcoidosis, and Lyme disease neuropathy.

Infrequently, adjacent dental fillings composed of dissimilar metals may trigger attacks,^[6] and one atypical case followed tongue piercing. Another case report of trigeminal neuralgia was reported in a patient with spontaneous intracranial hypotension; both conditions resolved following surgical treatment of a cervical root sleeve dural defect.^[7]

In 1968, Penman reported the US prevalence of trigeminal neuralgia (TN) as approximately 107 men and 200 women per 1 million people.^[8] By 1993, Mauskop noted approximately 40,000 patients have this condition at any particular time,^[9] with an incidence of 4-5 cases per 100,000. More recent estimates suggest the prevalence is approximately 1.5 cases per 10,000 population, with an incidence of approximately 15,000 cases per year.

Rushton and Olafson reported that approximately 1% of patients with multiple sclerosis (MS) develop trigeminal neuralgia,^[10] whereas Jensen et al noted that 2% of patients with trigeminal neuralgia have multiple sclerosis.^[11] Patients with both conditions often have bilateral trigeminal neuralgia.

No geographic tendency or racial differences have been found for trigeminal neuralgia. However, females are affected up to twice as often as males (range, 3:2 to 2:1). In addition, in 90% of patients, the disease begins after age 40 years, with a typical onset of 60-70 years (middle and later life). Patients who present with the disease when aged 20-40 years are more likely to suffer from a demyelinating lesion in the pons secondary to multiple sclerosis; younger patients also tend to have symptomatic or secondary trigeminal neuralgia . There have also been occasional reports of pediatric cases of trigeminal neuralgia.

Another risk factor for this syndrome is hypertension.

After an initial attack, trigeminal neuralgia (TN) may remit for months or even years. Thereafter the attacks may become more frequent, more easily triggered, disabling, and may require long-term medication. Thus, the disease course is typically one of clusters of attacks that wax and wane in frequency. Exacerbations most commonly occur in the fall and spring.

Among the best clinical predictors of a symptomatic form are sensory deficits upon examination and a bilateral distribution of symptoms (but the absence thereof is not a negative predictor). Young age is a moderate predictor, but a fair degree of overlap exists. Lack of therapeutic response and V1 distribution are poor predictors.

Although trigeminal neuralgia is not associated with a shortened life, the morbidity associated with the chronic and recurrent facial pain can be considerable if the condition is not controlled adequately. This condition may evolve into a chronic pain syndrome, and patients may suffer from depression and related loss of daily functioning. Individuals may choose to limit activities that precipitate pain, such as chewing, possibly losing weight in extreme circumstances. In addition, the severity of the pain may lead to suicide.

Complications

The chief complication in trigeminal neuralgia is the adverse effects and toxicity experienced routinely with long-term use of anticonvulsant agents. Another complication is the waning efficacy over several years of these drugs in controlling neuralgia, necessitating the addition of a second anticonvulsant, which may cause more drug-related adverse reactions.

Failure to diagnose a brainstem tumor and bone marrow aplasia as an idiosyncratic adverse effect of carbamazepine are common pitfalls to avoid.

Standard care must be applied to invasive procedures, which are most subject to potential claims. Percutaneous neurosurgical procedures and microvascular decompression procedures pose risks of long-term complications. Perioperative risks also exist. See Trigeminal Neuralgia Surgery. Moreover, patients may have to wait for weeks or months after the operation for relief, and some find relief only for 1-2 years and then must weigh the option of a second operation.

Some patients permanently lose sensation over a portion of the face or mouth. Occasionally, patients may suffer jaw weakness and/or corneal anesthesia. Corneal ulceration can result because of trophic disturbances from nerve deafferentation.

After any invasive treatments, reactivation of a herpes simplex infection is not uncommon.

The worst complication is anesthesia dolorosa, an intractable facial dysesthesia, which may be more disabling than the original trigeminal neuralgia. This dysesthesia may be caused by procedures and, sometimes, surgery.

Patients benefit from an explanation of the natural history of the disorder, including the possibility that the syndrome may remit spontaneously for months or even years before they need to consider long-term anticonvulsant medications. For this reason, some may elect to taper off their medication after the initial attack subsides; thus, they should be educated about the importance of being compliant with their medication regimen.

Patients also must be educated about the potential risks of anticonvulsant medications, such as sedation and ataxia, particularly in elderly patients, which may make driving or operating machinery hazardous. These drugs may also pose risks to the liver and the hematologic system. Document the discussion with the patient about these potential risks.

No specific preventative therapy exists. Patients may have a premonitory atypical pain for months; therefore, appropriate recognition of this pre–trigeminal neuralgia syndrome may lead to earlier and more efficient treatment.

Patients should avoid maneuvers that trigger pain. Once the diagnosis is established, advise them that dental extractions do not afford relief, even if pain radiates into the gums.

In patients wishing to undergo a procedure, they should be aware of potential adverse effects, as well as report any altered sensation in the face, especially after a procedure. They should be informed about the potential for anesthesia dolorosa.

Other resources

Some patients may wish to consult the resources below.

NINDS Trigeminal Neuralgia Information Page (updated: February 18, 2011)

NIH Neurological Institute

PO Box 5801

Bethesda, MD 20824

Phone: (800) 352-9424 or (301) 496-5751

TTY (for people using adaptive equipment): (301) 468-5981

E-mail: http://www.ninds.nih.gov/contact_us.htm

Web site: http://www.ninds.nih.gov/disorders/trigeminal_neuralgia/trigeminal_neuralgia.htm

TNA Facial Pain Association (formerly: Trigeminal Neuralgia Association)

408 W University Ave

Suite 602

Gainesville, FL 32601

Phone: (800) 923-3608 or (352) 384-3600

E-mail: info@fpa-support.org

Website: http://www.endthepain.org

An interactive questionnaire developed by the Oregon Health & Science University Department of Neurological Surgery allows patients to self-diagnose facial pain based on a brief series of questions. The "Trigeminal Neuralgia - Diagnostic Questionnaire" may be found at: https://neurosurgery.ohsu.edu/tgn.php (accessed April 7, 2011). An artificial intelligence method (neural network modeling) provides immediate feedback to the patient regarding the diagnosis and patient education resources.^[12]

For patient education information, see Brain & Nervous System Center, as well Trigeminal Neuralgia (Facial Nerve Pain), Tic Douloureux, and Pain Medications.