The term "neuralgia" is used to describe unexplained peripheral nerve pain, and the head and neck are two of the most common sites of such neuralgias. Trigeminal neuralgia, or TN, is by far the most frequently diagnosed form of neuralgia, with a mean incidence of 4 per 100,000 population1 and a mean age of 50 years at the time of examination.2 There is a female predominance ranging from 1:2 to 2:3.1,3
Clinicians must recognize trigeminal neuralgia and diagnose it correctly for patients to receive proper referral and therapy.
One of the first complete descriptions of TN was given by the English philosopher John Locke. In a letter dated December 1677, he described his encounter with the wife of an ambassador, the Countess of Northumberland, whom he was asked to see. 4 He reported that the countess experienced a fit of violent and exquisite torment that extended over the right side of her face and mouth. The term "tic douloureux" (painful jerking) was coined by Nicolaus Andre in 1756.5 However, it was not until 1773 at the Medical Society of London that John Fothergill gave a full and accurate description.6 TN also has been called Fothergill’s disease; however, this terminology is not encountered commonly today.
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CHARACTERISTICS OF TRIGEMINAL NEURALGIA
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TN is characterized by paroxysms of severe, lancinating, electriclike bouts of pain restricted to the distribution of the trigeminal nerve. The pain predominantly occurs unilaterally, most commonly on the right side, and involves the mandibular and/or maxillary branch or, rarely, the ophthalmic branch. Pain attacks occur spontaneously, and also are triggered by a nonpainful sensory stimulus to the skin, intraoral mucosa surrounding the teeth, or tongue. Anatomical trigger zones often can be identified. Each attack usually lasts only seconds to minutes, but they may be repeated at short intervals; consequently, individual attacks can overlap each other and may be described as a lingering, painful sensation. Attacks can occur at any time and are triggered not only by sensory stimuli to the face, but also by movement of the face (for example, chewing, yawning). Pain during the night that interrupts sleep is rare.7
TN usually has an exacerbating and remitting course, and patients experience shorter periods of remission as they age. In primary or idiopathic TN, physical examination does not reveal sensory or motor impairment of the trigeminal nerve. Idiopathic TN often is difficult to treat because the cause remains unknown, and despite the availability of multiple successful treatment options, no universally accepted medical and surgical treatment protocol exists.
It is important to differentiate TN from trigeminal neuropathy, in which sensory loss is prominent and pain usually is slight. This distinction can be detected with a careful physical examination. The pain of TN also differs from the pain following reactivation of the varicella zoster virus, which typically is seen in older people. When the varicella zoster virus involves the face, it has a predilection for the ophthalmic division of the trigeminal nerve.8 TN also is seen in patients with multiple sclerosis, or MS, and is the result of demyelinating lesions of the trigeminal root entry zone. This correlation between MS and TN ranges from 1 percent in one study9 to as high as 8 percent in another study.10
Trigeminal neuralgia usually has an exacerbating and remitting course, and patients with TN experience shorter periods of remission as they age.
In addition, patients with neuralgia-inducing cavitational osteonecrosis, or NICO, which has been described as a low-grade, nonsuppurative, radiographically invisible osteomyelitis of the jaws, may experience pain so similar to that of TN as to be confused with the condition.11 However, the diagnosis of NICO is somewhat controversial, and several authors have challenged the existence of this entity.12,13
The majority of cases of TN occur sporadically; however, the literature contains several reports of familial TN. A familial occurrence has been found in 4.1 percent of patients with unilateral TN and in 17 percent of patients with bilateral TN.14 In 1999, Duff and colleagues15 described a patient with familial TN and contralateral hemifacial spasm. The mother of the patient, five of his 10 siblings and one nephew also had TN confirmed by neurologists. An autosomal-dominant inheritance pattern would be consistent with this report and with previous reports in the literature; however, research has not established this inheritance pattern.
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PATHOGENESIS OF TRIGEMINAL NEURALGIA
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The pathogenesis of TN is uncertain. The disorder typically is idiopathic but may be due to a structural lesion. Several hypotheses have been stated, including traumatic compression of the trigeminal nerve by neoplastic (for example, cerebellopontine angle tumor) or vascular anomalies; infectious agents, including the human herpes simplex virus, or HSV; and demyelinating conditions, such as MS. A popular explanation is that TN arises secondary to a vascular loop that cross-compresses the trigeminal nerve a few millimeters proximal to the pons.16 This vulnerable area, known as the nerve root entry zone, marks the transition from central to peripheral myelin. Analogous cranial nerve neuralgias, such as hemifacial spasm and glossopharyngeal neuralgia, often involve similar lesions in their nerve root entry zones.17 Finally, a substantial number of patients may have concomitant dental problems, such as microabscesses, that may exacerbate the symptoms of TN, so dentists should evaluate all patients carefully for dental disease.18
Despite our relative lack of understanding of the pathophysiologic mechanisms of TN, effective surgical and medical treatments are available. Diagnostically, it makes sense to identify a potential cause of TN before initiating therapy. If TN has an identifiable cause, such as a tumor or mass compressing the nerve, the neurologist tailors the treatment toward elimination of the pathology or decompression of the nerve. In cases of idiopathic TN, clinicians consider medical and surgical options.
Latent infections of human HSV are common and therefore unlikely to be the sole cause of TN. Investigators have reported that HSV reactivation occurs commonly in patients who have undergone trigeminal rhizotomy, ganglion compression, balloon compression and percutaneous retrogasserian glycerol rhizotomy.19 This reactivation from latency is either a marker of altered trigeminal ganglion function or simply a consequence of surgical manipulation and a secondary reactivation of HSV. This distinction is not clear.
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TREATMENT
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Carbamazepine typically is used as the drug of first choice. Baclofen or clonazepam can be added if carbamazepine monotherapy is ineffective. When these treatments fail, however, monotherapy with phenytoin, pimozide or valproic acid is a reasonable alternative.16,18,20
Management algorithm.
Scrivani and colleagues7 reported the use of a TN management algorithm for patients with facial pain at the Massachusetts General Hospital, Boston. If the patient had paroxysmal, unilateral facial pain restricted to the trigeminal nerve, with no sensory deficit and identifiable trigger zones, the authors made a diagnosis of TN. Otherwise, the authors—who were members of a multidisciplinary facial pain group—evaluated the patient further.
Some surgical procedures may help in treating patients with multiple sclerosis, although the results generally are less effective or shorter-lasting than they are in other patients.
The authors reported that patients with TN underwent magnetic resonance imaging, or MRI, to reveal lesions, demyelinating plaques or vascular anomalies for which a neurological/neurosurgical consultation was obtained. In a patient whose MRI results were normal, the clinician prescribed a systematic trial of medications including carbamazepine, baclofen, phenytoin or gabapentin in different combinations, or prescribed one medication as a monotherapy. If the patient achieved pain relief, the clinician decreased the medication dosage slowly; however, if a recurrence occurred, the clinician reinstituted the medical therapy at the original dosage or prescribed a different combination of agents.
If patients did not achieve pain relief with pharmacological treatment, a neurosurgeon performed percutaneous radiofrequency thermal rhizotomy, or RTR. This is a well-established technique that involves controlled thermal ablation of nerve fibers in the trigeminal ganglion, with relative preservation of the sense of touch and of more complex facial sensations.21,22 In their group of 215 patients who underwent RTR between 1991 and 1996, Scrivani and colleagues7 reported that 198 (92 percent) achieved good or excellent pain relief at early follow-up (immediately after surgery to six months) and 178 (83 percent) achieved good-to-excellent pain relief at long-term follow-up (greater than six months to 68 months). The authors reported anesthesia dolorosa in only four patients (1.9 percent).
Surgical procedures.
In addition to RTR, surgical interventions for the treatment of TN include percutaneous retrogasserian glycerol rhizotomy,23 balloon compression24 and microvascular decompression, or MVD, of the trigeminal root.25 Some controversy exists regarding the surgical modality of choice. Some surgical procedures may help in treating patients with MS, although the results generally are less effective or shorter-lasting than they are in other patients.19 Successful treatment with MVD supports the hypothesis that peripheral nervous system abnormalities are the etiological mechanism of TN. The MVD surgical approach is based on the belief that vessels adjacent to the trigeminal nerve root compress it, which leads to the development of abnormal nerve stimulation. If this surgery removes the pain of TN, one might be able to conclude that the pathogenesis of TN is the result of vascular compression.
Imaging.
According to the algorithm used by Scrivani and colleagues,7 all patients with the diagnostic criteria for TN undergo MRI before they begin a trial of pharmacological therapy. However, other clinicians recommend the use of MRI only in patients in whom a trial of standard medications has been unsuccessful or in those who have atypical symptoms (such as bilateral or uncommon distribution, longer-than-usual pain duration, or both) to investigate whether demyelination, vascular compression or a tumor is the cause of the pain.2
In either case, MRI is the premier imaging modality in the diagnostic work-up of patients with TN, and it has surpassed computed tomography, or CT, and other imaging modalities that directly depict the anatomical relationship of the trigeminal nerve to any abnormal structures. The resolution of MRI is superior to that of CT for visualizing soft-tissue lesions. Magnetic resonance angiography, or MRA, a more recent imaging technique, allows visualization of the vascular anatomy of the relevant region without the use of contrast media. Contact between the constricting vascular loops and the nerve often can be imaged with MRI or MRA. The plaques of MS (a characteristic, ovoid, hyperintense structure highly suggestive of MS) also are better visu alized with MRI than with CT.
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REPORT OF A CASE
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A 50-year-old woman visited her general dentist complaining of episodes of severe pain in her right jaw that began two years previously. She described the pain as electrical and lancinating in nature, and explained that it occurred frequently while she applied makeup. Each episode lasted about one minute. The patient reported that the episodes initially occurred on several consecutive days, and then disappeared for several months. However, for the previous four weeks, the pain had been occurring almost every day. During the physical examination, the dentist found that mild pressure to the right V3 distribution reproduced the painful episode. He could not, however, identify any source of the pain on intraoral or extraoral examination, and referred the patient to us.
Because we could not identify any cause of the pain experienced by our patient, we made a diagnosis of idiopathic TN. We referred the patient to a neurologist, who prescribed carbamazepine (200 mg a day) and followed up the patient closely in the outpatient neurology clinic (measuring the carbamazepine level in the blood) for possible medication side effects and progression of the TN.
At two months’ follow-up, the patient had not experienced significant pain relief. Over several weeks, her neurologist increased her medication until a dosage of 1,200 mg per day was achieved. At the four-month follow-up visit, she reported having experienced significant improvement in her condition and could now apply makeup without triggering an episode. Approximately six months after the diagnosis, the patient’s neurologist conducted another physical examination, which did not reveal any signs of diplopia, nystagmus, lightheadedness, dizziness or lethargy. Laboratory analysis of the patient’s blood revealed no evidence of leukopenia or thrombocytopenia (potential side effects of the medication).
After the patient had been free of pain for four to six weeks, her neurologist gradually tapered the medication dosage, and eventually discontinued the treatment. The patient was followed up closely for more than one year for signs of potential relapse.
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CONCLUSION
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TN is the most common form of neuralgia, and patients often visit multiple clinicians complaining of severe pain. It is essential that clinicians recognize the disease and diagnose it correctly for patients to receive appropriate referral and therapy for this relatively treatable condition.
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ABSTRACT
CHARACTERISTICS OF TRIGEMINAL...
