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KEY POINTS
■ The diagnosis of trigeminal neuralgia is based largely on the history and physical examination.
■ For a patient with newly diagnosed idiopathic trigeminal neuralgia, the neurologic examination produces normal results and will not demonstrate any neurologic deficit of the trigeminal nerve or adjacent cranial nerves.
■ The primary medications used to treat trigeminal neuralgia symptoms are anticonvulsants. The first-line treatment is carbamazepine.
■ Multiple operative treatments are available and should be selected based on the patient's age and medical comorbidities.
More than 15,000 new cases of trigeminal neuralgia are diagnosed each year.
1,2 This condition is exceedingly painful, which makes it all the more important that health care providers be aware of the diagnostic workup and treatment options. Combing through the many choices available for pain relief can be challenging for patient and provider alike. This article reviews the pathophysiology, signs, and symptoms of trigeminal neuralgia and discusses both nonoperative and operative treatments.
THE SCOPE OF THE PROBLEM
Trigeminal neuralgia involves severe, lancinating pain, triggered by non-nociceptive stimuli, in the distribution of one or more divisions of the trigeminal nerve.3,4 The condition is also known as ticdouloureux because of the brief but severely painful ticlike spasms that characterize it. Although the pain typically lasts only a few seconds, it can be excruciating.5 Pain is typically triggered by sensory stimuli, including chewing, speaking, yawning, brushing the teeth, or eating. Often patients are forced to modify or even cease activities such as eating or talking so as to decrease the frequency of the pain. The condition may be relapsing, with pain-free intervals varying from a few days to several years. The episodic pain that patients endure with this disease can be treated both medically and surgically.
The annual incidence of trigeminal neuralgia has been reported as 4 cases per 100,000 population.4,6 Incidence gradually increases with age, and the condition is rare before age 40 years.4,6 The average age of onset is 60 years,7 and trigeminal neuralgia develops slightly more often in women than men.4,8
ANATOMY AND PATHOPHYSIOLOGY
The trigeminal nerve is the fifth cranial nerve. It is the largest of the 12 cranial nerves, with three divisions often designated as V1 (first, the ophthalmic division), V2 (second, the maxillary division), and V3 (third, the mandibular division). The most affected territories in trigeminal neuralgia are the maxillary (V2) and the mandibular (V3) divisions, though any single distribution or combination on a given side of the face may occur.4 The ophthalmic and maxillary nerves are purely sensory, whereas the mandibular nerve has both sensory and motor functions. The ophthalmic division mediates sensation of the upper half of the head and face, including the area around the eyes and the tip of the nose. The maxillary division provides sensation to the midface, including the upper lip, oral cavity, and maxillary teeth. The sensory component of the mandibular division carries sensation to the lower part of the face, including the chin, inferior oral cavity and teeth, and buccal tissues (Figure 1). The motor component of the mandibular branch is responsible for temporalis, masseter, and pterygoid function.
The etiology of trigeminal neuralgia is thought to be segmental demyelinization of trigeminal sensory fibers, either within the nerve root or brain stem. In most cases, the demyelinization is secondary to chronic compression of the trigeminal root at or near its exit from the pons.2,5,8 In some cases, the compression can be caused by pathology including vascular abnormalities such as an aneurysm or arteriovenous malformation or benign tumors such as epidermoids, neurofibroma, or meningioma within the cerebellopontine angle.9 Demyelinization due to multiple sclerosis may also cause typical symptoms of trigeminal neuralgia.2
These structural pathologies and demyelinating diseases must be considered when first evaluating a patient with trigeminal neuralgia. A good neurologic history and examination, plus brain imaging with contrast and noncontrast CT or, optimally, MRI, are often part of an initial evaluation. Most often no structural abnormality is identified, and a diagnosis of idiopathic trigeminal neuralgia is made. In 80% to 90% of cases of idiopathic trigeminal neuralgia, compression of the trigeminal root as it exits the brainstem by a loop of artery or, less often, a vein has been found to be the cause.5
The exact pathophysiology of idiopathic trigeminal neuralgia remains a topic of debate, but the neurovascular compression/demyelinization theory remains the most plausible and widely accepted explanation.4-6 This theory proposes that vascular compression of the trigeminal root leads to segmental demyelination and ephaptic transmission of trigeminal impulses.5 Ephaptic transmission occurs when neuronal impulses are transmitted directly from one nerve fiber to another without an intermediate neurochemical synapse. Experimental studies indicate that demyelinated axons are prone to ephaptic cross-talk, which may transfer impulses from light touch to pain fibers in close proximity (ephaptic conduction). Current theories regarding the cause of the demyelination center on vascular compression of the nerve root at its exit zone from the pons.1,5,7 The most common vessel causing vascular compression of the trigeminal root in this region is the superior cerebellar artery, but an ectatic basilar artery and constricting petrosal veins have also been implicated on inspection at operation.9,10