How to treat: Trigeminal neuralgia

Trigeminal neuralgia is often described as a "forked lightning" pain in the face. Andria Merrison and Geraint Fuller take a look at medical and surgical treatment options for this common condition

Patients describe the sudden and severe pain of trigeminal neuralgia as a "red hot needle" or a "forked lightening" pain in the face. The French term "tic doloreux" emphasises the suddenness of the pain that may be triggered by touch or cold. This characteristic pain affects four to five people in 100 000. It occurs in bouts lasting weeks or months, with months or years of remission. Evidence is increasing that in most patients trigeminal neuralgia is caused by compression of the trigeminal nerve root, close to its entry into the pons, by an aberrant arterial or venous loop.¹ Other compressive lesions are responsible in a few patients. About 2% of patients with trigeminal neuralgia have multiple sclerosis.

First line treatment

Standard first line treatment is carbamazepine.²³ Other drugs, including lamotrigine, phenytoin, gabapentin, oxcarbazepine, topiramate, baclofen, and clonazepam have some effect, although studies are more limited.³ Many patients fail to have a sustained response to drugs, and this article looks at the possible "non-drug" options for such patients.

Other interventions

Interventions for patients with an unsatisfactory response to medical treatment include microvascular decompression, which treats the putative cause surgically by separating the trigeminal nerve from adjacent blood vessels, and a variety of methods of producing a partial trigeminal nerve lesion, including neurectomy; radio frequency thermal ablation; balloon compression; glycerol injections; and radiosurgery. The evidence for these treatments for trigeminal neuralgia does not come from randomised trials.² People who treat patients with the severe pain of trigeminal neuralgia are often readily convinced of the effectiveness of an intervention by the timing of pain relief. This influences the clinical uncertainty that might otherwise lead to doing formal trials and particularly to using placebo controls. Given the severity of the pain, unsurprisingly, no studies have followed untreated patients with trigeminal neuralgia, so the rate of spontaneous remission is not known.

Microvascular decompression

Some large sequential case series from specialist centres report that microvascular decompression renders over two thirds of patients pain free at 10 years, with 1% experiencing facial numbness.⁴ Other studies are less optimistic and highlight complications, which include injury to the cerebellar nerve and eighth cranial nerve⁵ and death rates of 0.2-1%.⁶ Newer techniques in magnetic resonance imaging may identify microvascular compression more readily and thus improve the selection of patients. Microvascular decompression offers a treatment that is designed not to damage the trigeminal nerve and has good results in expert hands. However, the treatment carries a small but definite risk of serious, including fatal, complications and, like all surgical procedures, depends on the surgeon.

SUNSET/REX FEATURES

Destructive lesions

Destructive lesions provide a safer alternative at the cost of greater loss of trigeminal function. This sensory loss can occasionally itself be painful--so called anaesthesia dolorosa. Balloon compression or radio-frequency thermal ablation of the trigeminal ganglion, glycerol injections into the trigeminal cistern, and neurectomy are alternatives, with some success reported. Generally greater sensory loss seems to be associated with less frequent recurrence of pain. Numbness or dysaesthesia is reported in over 15% of patients treated with these techniques. The reported long term benefits vary widely (25-80%) depending on duration of follow up and how response to treatment is defined.

Stereotactic gamma knife radiosurgery

Stereotactic gamma knife radiosurgery, the newest destructive procedure, entails the delivery of a focused beam of radiotherapy to a target--in this case the proximal trigeminal nerve. First used in 1951, the procedure has been more widely used since the mid-1990s. As with all non-drug interventions for trigeminal neuralgia, the evidence is based on case series, with a single randomised study comparing two methods of delivery of radiotherapy.⁷ The case series have different patient populations, varying doses of radiation and targets, a variety of assessment methods, and differing follow up. However, reports are encouraging, with 70-80% of patients describing freedom from pain in the short term,^{8 9 10} although up to 50% may relapse.¹¹ Side effects include facial dysaesthesia (up to 12%), corneal irritation, vascular damage, hearing loss, and facial weakness, varying with the dose schedule and target area. Follow up is short compared with the 10 years cited for other treatment modalities, and uncertainty persists about possible late complications of radiotherapy--for example, cerebral oedema or neoplastic transformation.

The level of evidence for radiosurgery falls short of that routinely expected for drug treatment. However, the same is true for all non-drug interventions used for this condition. The National Institute for Clinical Excellence (NICE) recently issued a consultation document on stereotactic radiosurgery for trigeminal neuralgia.¹² It has provisionally decided that the evidence is inadequate to support its use without special arrangements for audit or research and that it should be the subject of a systematic review. This seems reasonable and hopefully will lead to further studies.

Andria F A Merrison specialist registrar, Geraint Fuller consultant neurologist, Department of Neurology, Gloucestershire Royal Infirmary, Gloucester GL1 3NN
Email: geraint@FullerG.demon.co.uk


studentBMJ 2004;12:1-44 February ISSN 0966-6494

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