6th cn

Trigeminal neuralgia is severe paroxysmal, lancinating facial pain due to a disorder of the 5th cranial nerve. Diagnosis is clinical. Treatment is usually with carbamazepine or gabapentin; sometimes surgery is required.

Trigeminal neuralgia affects mainly adults, especially the elderly.

Etiology

Trigeminal neuralgia is usually caused by an intracranial artery (eg, anterior inferior cerebellar artery, ectatic basilar artery) or, less often, a venous loop that compresses the 5th cranial (trigeminal) nerve at its root entry zone into the brain stem. Other less common causes include compression by a tumor and occasionally a multiple sclerosis plaque at the root entry zone, but these causes are usually distinguished by accompanying sensory and other deficits. Other disorders that cause similar symptoms (eg, multiple sclerosis) are sometimes considered to be trigeminal neuralgia and sometimes not. Recognizing the cause is what is important.

The mechanism is unclear. One theory suggests that nerve compression causes local demyelination, which may result in ectopic impulse generation and/or disinhibition of central pain pathways involving the spinal trigeminal nucleus.

Symptoms and Signs

Pain occurs along the distribution of one or more sensory divisions of the trigeminal nerve, most often the maxillary. The pain is paroxysmal, lasting seconds up to 2 min, but attacks may recur rapidly. It is lancinating, excruciating, and sometimes incapacitating. Pain is often precipitated by stimulating a facial trigger point (eg, by chewing, brushing the teeth, or smiling). Sleeping on that side of the face is often intolerable.

Diagnosis

Clinical evaluation

Symptoms are almost pathognomonic. Thus, some other disorders that cause facial pain can be differentiated clinically:

Chronic paroxysmal hemicrania (Sjaastad syndrome) is differentiated by longer (5 to 8 min) attacks of pain and its dramatic response to indomethacin

.

Postherpetic pain is differentiated by its constant duration (without paroxysms), typical antecedent rash, scarring, and predilection for the ophthalmic division.

Migraine, which may cause atypical facial pain, is differentiated by pain that is more prolonged and often throbbing.

Neurologic examination is normal in trigeminal neuralgia. Thus, neurologic deficits (usually loss of facial sensation) suggest that the trigeminal neuralgia–like pain is caused by another disorder (eg, tumor, stroke, multiple sclerosis plaque, vascular malformation, other lesions that compress the trigeminal nerve or disrupt its brain stem pathways).

Treatment

Usually anticonvulsants

Carbamazepine

200 mg po tid or qid is usually effective for long periods; it is begun at 100
mg po bid, increasing the dose by 100 to 200 mg/day until pain is controlled (maximum daily dose 1200 mg). If carbamazepine

is ineffective or has adverse effects, one of the following
may be tried:

Oxcarbazepine

150 to 300 mg po bid

Gabapentin

300 to 600 mg po tid (300 mg po once on day 1, 300 mg po bid on day 2,
300 mg po tid on day 3, then increasing dose as needed to 600 mg po tid)

Phenytoin

100 to 200 mg po bid (beginning with 100 mg po bid, then increasing as
needed)

Baclofen

10 to 30 mg po tid (beginning with 5 to 10 mg po tid, then increasing as needed
by about 5 mg/day)

Amitriptyline

25 to 150 mg po taken at bedtime (beginning with 25 mg, then increasing
by 25-mg increments each week as needed)

Peripheral nerve block provides temporary relief.

If pain is severe despite these measures, neuroablative treatments are considered; however, efficacy may be temporary, and improvement may be followed by recurrent pain that is more severe than the preceding episodes. In a posterior fossa craniectomy, a small pad can be placed to separate the pulsating vascular loop from the trigeminal root. In radiosurgery, a gamma knife can be used to cut the proximal trigeminal nerve. Electrolytic or chemical lesions or balloon compression of the trigeminal (gasserian) ganglion can be made via a percutaneous stereotactically positioned needle. Occasionally, the trigeminal nerve fibers between the gasserian ganglion and brain stem are cut. Sometimes, as a last resort to relieve intractable pain, the trigeminal nerve is destroyed.

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