CHAPTER 160 Trigeminal Neuralgia
Diagnosis and Nonoperative Management
Neuropathic facial pain (NFP) is defined as pain around the mouth or face that arises from a primary lesion or dysfunction of the nervous system.1 The management of NFP can be a frustrating as well as rewarding experience in neurosurgical practice because facial pain is often a difficult problem with a wide variety of potential causes. It is therefore important for neurosurgeons to have a broad understanding of the underpinnings of facial pain syndromes. NFP can be primary (with no recognizable underlying pathology) or secondary, such as following traumatic nerve injury. NFP includes a heterogeneous group of entities and can be broadly considered in two categories: paroxysmal and continuous.2 Paroxysmal neuropathies such as trigeminal neuralgia (TN) are characterized by short electrical shock-like or sharp pain. Continuous pain often has a burning characteristic and is a common feature of conditions such as postherpetic neuralgia (PHN). NFP can vary in severity and also commonly presents with thermal or mechanical allodynia.
Historical Perspective
One of the earliest known descriptions of paroxysmal facial pain was by the Arab physician Jurjani in the 11th century. He described “a type of pain which affects the teeth on one side and the whole of the jaw on the side which is painful.”3 The 17th century physician John Locke described the symptoms of TN in the wife of the English ambassador to France. Faced with limited treatment options for the patient’s excruciating pain, the physician opted for eight rounds of cleansing of the gastrointestinal tract, which reportedly resulted in remission of symptoms.4
In the era preceding the description of TN, studies of the anatomy of the cranial nerves led to a better understanding of facial pain. In 1829, the Scottish anatomist Sir Charles Bell (1774-1842) described the anatomy of the fifth cranial nerve and its motor and sensory functions, establishing the trigeminal nerve as the cranial nerve responsible for subserving facial sensation as well as motor innervation to the masticator muscles.5 Previously, it was widely believed that the seventh cranial nerve was the source of facial pain syndromes. Bell’s discovery shifted the focus of investigation of facial pain syndromes from the seventh to the fifth cranial nerve.3
An important breakthrough in the management of TN occurred fortuitously in 1942 when Bergouignan administered his patients the then new anticonvulsant diphenylhydantoin (phenytoin).6 Before this, the condition was referred to as neuralgia epileptiform owing to a prior hypothesis by Trousseau in 1853 that TN being paroxysmal was related to abnormal impulse conduction, analogous to epilepsy.7 When carbamazepine, a new medication for epilepsy was introduced in 1962, it was soon found to be useful in patients with TN.8,9 It had greater efficacy and less toxicity than the hydantoins and remains to this day the mainstay of medical therapy.10
General Principles in the Medical Management of Facial Pain
The initial treatment of most facial pain syndromes is medical. The differential diagnosis of facial pain includes pathology involving nerves, teeth and jaw, sinuses, the aerodigestive tract, and blood vessels and is summarized in Table 160-1. Treatment must be driven by proper diagnosis and the characteristic features of the pain (Fig. 160-1). Pain due to head or neck neoplasm is best treated by treatment of the lesion. Similarly, psychogenic pain is best managed by treatment of the underlying psychiatric condition. It is important to distinguish nociceptive from neuropathic pain. Nociceptive pain is caused by normal and appropriate neural activity in the setting of local tissue injury (e.g., trauma, malignancy, infection). Nociceptive pain is typically constant and aching and only occasionally paroxysmal. Besides appropriate management of the underlying condition, nociceptive pain is best managed by opioid medications.
| LOCATION OF LESION | CONDITION |
|---|---|
| Nerve | Trigeminal neuralgia, postherpetic neuralgia, trigeminal neuropathic pain, glossopharyngeal neuralgia, sphenopalatine neuralgia, geniculate neuralgia (Ramsay Hunt syndrome), multiple sclerosis, cerebellopontine angle tumor |
| Teeth and jaw | Dentinal, pulpal, or periodontal pain; temporomandibular joint disorders |
| Sinuses and aerodigestive tract | Sinusitis, head and neck cancer, inflammatory lesions |
| Eyes | Optic neuritis, iritis, glaucoma |
| Blood vessels | Giant cell arteritis, migraine, cluster headache, Tolosa-Hunt syndrome |
| Psychological | Psychogenic, atypical facial pain |
Trigeminal Neuralgia
TN, a neuropathic pain syndrome, is defined by the International Association for the Study of Pain (ISAP) as “a sudden and usually unilateral severe brief stabbing recurrent pain in the distribution of one or more branches of the fifth cranial nerve.” It is an excruciating, short-lasting (<2 minutes), unilateral facial pain that may be spontaneous or triggered by gentle, innocuous stimuli and separated by pain-free intervals of varying duration (Fig. 160-2).
FIGURE 160-2 Major clinical features of trigeminal neuralgia.
(From Zakrzewska JM, Linskey ME. Trigeminal neuralgia. In: Zakrzewska JM, ed. Orofacial Pain. New York: Oxford University Press; 2008, pp 119-134.)
Most TN patients (>85%) have classic TN. Diagnosis in typical cases is often straightforward; however, most TN patients suffer from misdiagnosis. Common conditions that mimic TN as well as their presenting features are listed in Table 160-2.
TABLE 160-2 Common Conditions that Mimic Trigeminal Neuralgia
| DIAGNOSIS | IMPORTANT FEATURES |
|---|---|
| Dental infection or cracked tooth | Well localized to tooth; local swelling and erythema; appropriate findings on dental examination |
| Temporomandibular joint pain | Often bilateral and may radiate around ear and to neck and temples; jaw opening may be limited and can produce an audible click |
| Persistent idiopathic facial pain (previously called atypical facial pain) | Often bilateral and may extend out of trigeminal territory; pain often continuous, mild to moderate in severity, and aching or throbbing in character |
| Migraine | Often preceded by aura; severe unilateral headache often associated with nausea, photophobia, phonophobia, and neck stiffness |
| Postherpetic neuralgia | History of herpes zoster or vesicular outbreak |
| Temporal arteritis | Common in elderly people; temporal pain should be constant and often associated with jaw claudication, fever, and weight loss; temporal arteries may be firm, tender, and nonpulsatile on examination |
Adapted from Bennetto L, Patel NK, Fuller G. Trigeminal neuralgia and its management. BMJ. 2007;334:201-205.
Etiology and Pathophysiology
Considerable progress has been made in elucidating the etiology of TN. In most patients with classic TN, the pain is generated because of compression of the trigeminal nerve most commonly at the root entry zone by an artery or vein. Observations supporting this are summarized in Table 160-3. The plaques of demyelination lead to hyperexcitability of injured afferents, which results in after discharges large enough to result in a non-nociceptive signal being perceived as pain.11 One theory to explain TN is the one proposed by Devor and colleagues,12 called the ignition theory, which can be explained as follows. The triggering of pain in TN may follow innocuous stimuli, a phenomenon that is probably explained by postinjury changes in neuronal function. After nerve injury, there is an increased proportion of A-beta fibers with subthreshold oscillations that ultimately generate ectopic discharges.13–15 These produce a transient depolarization in neighboring passive C neurons in the same ganglion.16
