Cranial Neuralgias—Trigeminal Neuralgia

Classic trigeminal neuralgia, also known as tic douloureux, presents as paroxysmal attacks of severe, sharp, or stabbing pain in the cutaneous distribution of one or more divisions of the trigeminal nerve. This pain usually starts in the second or third divisions, affecting the cheek or the chin. The first division is affected alone in less than 5% of patients. These attacks may last from a fraction of a second to 2 minutes, occur multiple times per day, and tend to be stereotypic in nature.

Attacks of pain are often provoked by sensory stimuli, such as light touch, cold air or cold liquid over the face or gums (especially in small supersensitive areas known as “trigger zones”), or movements, such as talking, chewing, shaving, puckering lips, or brushing teeth. The paroxysm of pain may be followed by a refractory period where stimulation does not trigger pain. The pain is strictly unilateral. In the rare cases of bilateral trigeminal neuralgia, the episodic painful paroxysms are asynchronous and are independently triggered. Between attacks, the patient is usually pain free, although over time, some patients notice a dull or burning continuous pain in the same area.

The temporal profile of trigeminal neuralgia may be fluctuating with exacerbations and spontaneous remissions lasting weeks to months, or even years. Patients with classic trigeminal neuralgia have a normal neurologic examination. The presence of a sensory deficit within the distribution of the trigeminal nerve suggests a trigeminal neuropathy and may indicate a secondary cause for the pain symptoms.

Although pathogenesis of trigeminal neuralgia is not completely understood, it is thought that the neuralgic pain is related to a chronic focal demyelination secondary to damage to the trigeminal nerve, usually within a few millimeters of where the nerve enters the pons, that is, the root entry zone. This damage is most often due to compression of the nerve by an aberrant loop of artery or vein. Rarely, this focal demyelination may also be caused by an aneurysm, arteriovenous malformation, or a neoplasm (i.e., trigeminal neuroma acoustic neuroma, epidermoid, or a meningioma). Demyelination from multiple sclerosis (MS) requires primary consideration in any young adult presenting with trigeminal neuralgia, and this is especially suspect in patients presenting with bilateral symptoms. Contrast-enhanced magnetic resonance imaging (MRI) with special sequencing of the trigeminal nerve should be performed to assess the patient for possible demyelination or a mass lesion.

There are several therapeutic options for individuals with trigeminal neuralgia. Most patients respond to carbamazepine. Other medications that may be effective include gabapentin, baclofen, or oxcarbazepine.

Patients who have failed or become intolerant to medical therapy are candidates for a variety of surgical procedures consisting of either microvascular decompression or nerve ablation. When treating the patient with open surgery, the aberrant vessel is separated from the nerve while a piece of surgical mesh is introduced between the aberrant vessel and the nerve. Surgical risks include damage to the nerve or surrounding structures, including damage to the auditory or facial nerves.

When an ablative procedure is used, the therapeutic goal is to precisely damage the trigeminal nerve so that it no longer transmits the pain signal well. These procedures include radiofrequency thermocoagulation, mechanical balloon compression, chemical (glycerol) injection, or gamma knife radiosurgery. Because the nerve is inherently damaged with these modalities, ablative procedures are accompanied by varying degrees of sensory loss. Unfortunately, trigeminal neuralgia has the potential to recur after any procedure, and may require repeat intervention.

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