trigeminal neuralgia

Pathophysiology

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. Among the structural causes, damage to the myelin sheath of this nerve causes the electrical impulses traveling along it to be erratic or excessive, activating pain regions or deactivating pain inhibitory regions in the brain. The damage may be caused by an aneurysm (an outpouching of a blood vessel) or abnormally coursing artery compressing the nerve, most frequently at the area of its cerebellopontine nerve root; the superior cerebellar artery has been an oft-cited culprit. 2 to 4% 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. Trigeminal Neuralgia may also be caused by a tumor, an arachnoid cyst in the cerebellopontine angle^[1], or a traumatic event such as a car accident. 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, sometimes triggered by common activities or cold exposure, and are said to feel like stabbing electric shocks. Individual attacks affect one side of the face at a time, last several seconds, and may come and go throughout the day, or for periods as long as several months. 3-5% of cases are bilateral, and attacks may increase in frequency or severity over time. 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. 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.

Treatment

There is no cure for trigeminal neuralgia, but it can be treated with anticonvulsants such as carbamazepine (Tegretol), phenytoin, or gabapentin (Neurontin). 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. Pain may be treated long-term with an opioid such as methadone in some patients, but due to the nature of the neuralgia, traditional analgesics typically have negligible effect. Low doses of some antidepressants such as nortriptyline can also be effective in treating neuropathic pain. Surgery may be recommended, either to relieve the pressure on the nerve or to damage it further to prevent the transmission of pain. Surgery is effective in more than 75% of people with classic trigeminal neuralgia. The nerve can also be damaged to prevent pain signal transmission using a fine beam of radiation, so-called gamma knife. This 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). 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 (MVD).

Atypical trigeminal neuralgia is more difficult to treat, both with medications and surgery. Surgery may result in areas of numbness bothersome to the patient and lead occasionally to "anesthesia dolorosa," which is numbness with intense pain. It should, however, be noted that many people do find dramatic relief with minimal side effects from the various surgeries that are available.

Capsaicin can be helpful in short term temporary pain control of trigeminal neuralgia. It works by over stimulating the nerve endings at the site of current trip points on the face.

Sources

• Natarajan M. Percutaneous trigeminal ganglion balloon compression : experience in 40 patients. Neurol India 2000, cited 2005 Feb 6;48:330-2.

References

1. ^ Babu R, Murali R. "Arachnoid cyst of the cerebellopontine angle manifesting as contralateral trigeminal neuralgia: case report", Neurosurgery 1991 Jun;28(6):886-7. (PMID 2067614)

External links

• Trigeminal Neuralgia Association
• Facial neuralgia
• About surgery for trigeminal neuralgia
• MedlinePlus Overview trigeminalneuralgia
• My Trigeminal neuralgia - a personal story.
• Centre for Cranial Nerve Disorders.