Trigeminal Neuralgia

Trigeminal neuralgia (TN), tic douloureux (also known as prosopalgia) is a neuropathic disorder of one or both of the trigeminal nerves. Its nickname is "the suicide disease" because of severe associated pain, and the fact that it is not easily controlled or cured. It causes episodes of intense pain in any or all of the following: the ear, eye, lips, nose, scalp, forehead, teeth, or jaw on one side and alongside of the face. It is estimated that 1 in 15,000 people suffer from trigeminal neuralgia, although the actual figure may be significantly higher due to frequent misdiagnosis. TN usually develops after the age of 50, more commonly in females, although there have been cases with patients being as young as three years of age.

TN brings about stabbing, mind-numbing, electric shock-like pain from just a finger touch to the cheek, or even spontaneously without any stimulation of the patient. Cold wind, high pitched sounds, loud noises such as concerts or crowds, chewing, and talking can aggravate the condition, and for the worst cases even smiling, wearing a scarf, the wind or hair on the side of the face is too much to bear.

Pathophysiology, causes, and differential diagnosis

The symptoms of trigeminal neuralgia are often falsely attributed to a pathology of dental origin. "Rarely do patients come to the surgeon without having removed many, and not infrequently all, teeth on the affected side or both sides." Extractions do not help. The pain is originating in the trigeminal nerve itself – often in its roots – and not in an individual nerve of a tooth but real tooth pain may be referred to the same areas of the face as that of trigeminal neuralgia. Because of this difficulty, many patients go untreated unless 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. It was once believed that the nerve was compressed in the opening from the inside to the outside of the skull; but newer leading research indicates that it is an enlarged blood vessel – possibly the superior cerebellar artery – compressing or throbbing against the microvasculature of the trigeminal nerve near its connection with the pons. 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 may rarely be caused by an aneurysm (an outpouching of a blood vessel); by a tumor; by an arachnoid cyst in the cerebellopontine angle; or by a traumatic event such as a car accident or even a tongue piercing.

A large portion of multiple sclerosis patients have TN, but not everyone with TN has MS. Only 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. It has been theorized that this is due to damage to the spinal trigeminal complex. Trigeminal pain has a similar presentation in patients with and without MS.

Postherpetic Neuralgia, which occurs after shingles, may cause similar symptoms if the trigeminal nerve is damaged.

When there is no structural cause, the syndrome is called idiopathic.

Symptoms

The disorder is characterised by episodes of intense facial pain that usually last from a few seconds to several minutes or hours. The episodes of intense pain may occur paroxysmally. To describe the pain sensation, patients may describe a trigger area on the face, so sensitive that touching or even air currents can trigger an episode. It affects lifestyle as it can be triggered by common activities such as eating, talking, shaving and toothbrushing. The attacks are said by those affected to feel like stabbing electric shocks, burning, pressing, crushing, exploding or shooting pain that becomes intractable.

Individual attacks usually affect one side of the face at a time, lasting from several seconds to a few minutes and repeat up to hundreds of times throughout the day. The pain also tends to occur in cycles with remissions lasting months or even years. 10-12% 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. Many patients develop the pain in one branch, then over years the pain will travel through the other nerve branches.

Outwardly visible signs of TN can sometimes be seen in males who may deliberately miss an area of their face when shaving, in order to avoid triggering an episode. Successive recurrences are incapacitating and the dread of provoking an attack may make sufferers unable to engage in normal daily activities.

There is also 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 shock-like pains. This variant is often called "trigeminal neuralgia, type 2", based on a recent classification of facial pain. 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. Some recent studies suggest that ATN may be an early development of Trigeminal Neuralgia.

Treatment

As with many conditions without clear physical or laboratory diagnosis, TN is unfortunately sometimes misdiagnosed. A TN sufferer will sometimes seek the help of numerous clinicians before a firm diagnosis is made.

There is evidence that points towards the need to quickly treat and diagnose trigeminal neuralgia (TN). It is thought that the longer a patient suffers from TN, the harder it may be to reverse the neural pathways associated with the pain.

Dentists who suspect TN should proceed in the most conservative manner possible and should ensure that all tooth structures are "truly" compromised before performing extractions or other procedures.

Medications

• Anticonvulsants are a common treatment strategy for trigeminal neuralgia. Carbamazepine is the first line drug; second line drugs include baclofen, lamotrigine, oxcarbazepine, phenytoin, gabapentin, and sodium valproate. Uncontrolled trials have suggested that clonazepam and lidocaine may be effective.
• Low doses of some antidepressants such as amytriptiline are thought to be effective in treating neuropathic pain, but a tremendous amount of controversy exists on this topic, and their use is often limited to treating the depression that is associated with chronic pain, rather than the actual sensation of pain from the trigeminal nerve.
• 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.
• Patients may also find relief by having their neurologist implant a neuro-stimulator.

Many patients cannot tolerate medications for years, and an alternative treatment is to take a drug such as gabapentin and apply it externally. This preparation is prepared extemporaneously by pharmacists. Also helpful is taking a "drug holiday" when remissions occur and rotating medications if one becomes ineffective.

• Opiates such as morphine and oxycodone can be prescribed, and there is evidence of their effectiveness on neuropathic pain, especially if combined with gabapentin.
• A case report found sumatriptan effective in the management of drug-resistant Trigeminal Neuralgia.

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, surgery has been reported to have an initial success rate approaching 90 percent. However, some patients require follow-up procedures if a recurrence of the pain begins.

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 25-millimetre (1 in) 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, usually made from an inert surgical material such as Teflon. 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. 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. Trilogy, Novalis, CyberKnife). No incisions are involved in this procedure. It uses very precisely targeted 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, heparin, aspirin). 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.

There has only been one prospective clinical trial for surgical therapy for trigeminal neuralgia. In a prospective cohort trial, microvacular decompression was found to be significantly superior to stereotactic radiosurgery in achieving and maintaining a pain-free status in patients with trigeminal neuralgia and provided similar early and superior longer-term patient satisfaction rates compared with those treated with stereotactic radiosurgery.

Social consequences of trigeminal neuralgia

Most suffers of TN do not present with any outwardly noticeable symptoms, though some will exhibit brief facial spasms during an attack. Some physicians will seek a psychological root cause rather than a physiological abnormality. This is especially true of those suffering from atypical TN, who may not have any compression of the TN and in whom the sole criterion of the diagnosis may be the complaint of severe pain (constant electric-like shocks, constant crushing or pressure sensations, or a constant severe ache) and in this case trigeminal neuralgia still exists but is not visible to physicians because it was caused by the nerve being damaged during a dental procedure such as root canals, extractions, gum surgeries or it may be a condition secondary to multiple sclerosis.

Many TN sufferers are confined to their homes or are unable to work because of the frequency of their attacks. It is important for friends and family to educate themselves on the intense severity of TN pain and to be understanding of limitations that TN places upon the sufferer. However, at the same time, the TN patient must be extremely proactive in furthering his or her rehabilitative efforts. Enrolling in a chronic pain support group, or seeking one-on-one counseling, can help to teach a TN patient how to adapt to the newfound affliction.

As with any chronic pain syndrome, TN not being the exception, clinical depression has the potential to set in, especially in younger patients who often are undertreated for chronic pain. Friends and family, as well as clinicians, must be alert to the signs of a rapid change in behavior and should take appropriate measures when necessary. It must be constantly reinforced to the sufferer of TN that treatment options do exist.

Other

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

Some patients have reported a correlation between dental work and the onset of their trigeminal nerve pain.

Recently, some researchers have investigated the link between neuropathatic pain, such as TN, and coeliac disease.