Chapter 202

Trigeminal Neuralgia

Wanda J. Handel

Definition and Epidemiology

Trigeminal neuralgia is a common and well-defined pain disorder affecting the sensory branches of the trigeminal nerve. It is also known as tic douloureux, from the French for “painful spasm,” and affects 12 people per 100,000.¹ Women are affected slightly more often than men (3 : 2), and older adults more often than younger persons. The mean age at onset is 54 years; most cases occur in individuals 50 to 70 years of age. Cases occurring in patients younger than 40 years are unusual.¹

Pathophysiology

The fifth cranial nerve, the trigeminal nerve, is a large, mixed sensory and motor nerve that originates in the brainstem and travels in the cervical cord, with the sensory ganglion found in the Meckel cave in the middle cranial fossa. The peripheral branches form three sensory divisions—ophthalmic (V1), maxillary (V2), and mandibular (V3)—that conduct sensory impulses from the greater part of the face and head, from the cornea and conjunctiva, and from the nose and mouth. These impulses eventually terminate in the thalamus, where they are relayed to the appropriate cortical area for interpretation. The motor portion of the nerve supplies the muscles of the jaw and sphenoid areas.

Most primary cases of trigeminal neuralgia are thought to be caused by vascular compression and are considered classic trigeminal neuralgia.² Secondary trigeminal neuralgia is differentiated by the ability to demonstrate a structural cause, such as compression, trauma, or multiple sclerosis.³ The location of one of the cerebral arteries and its branches is thought to be a factor by creating compression on the nerve as it exits the brainstem. Demyelination, vascular changes, and degenerative changes in the sensory (gasserian) ganglion are postulated to generate altered impulse transmission, allowing ephaptic transmission between adjacent nerve fibers mediating light touch and pain.⁴

Clinical Presentation

The primary feature of this disorder is recurrent paroxysms of pain in the distribution of any branch of the trigeminal nerve. The pain is usually described as burning, stabbing, sharp, penetrating, or electric shock–like and usually is on one side of the face. Males may have unshaven faces or portions thereof. The index of suspicion for multiple sclerosis rises if the patient exhibits bilateral facial pain. The duration of each paroxysm varies from seconds to more than 15 minutes and involves V2 and V3 more often than V1; V1 is more frequently affected by postherpetic neuralgia.⁵ Pain may recur once a month or several times per day. If the pain occurs frequently during the day, the patient may report unremitting facial discomfort between discrete episodes. Usually, a patient does not awaken from sleep during a paroxysm.

During an attack, the patient may cease talking, stop chewing, become very still, rub or pinch the face, avoid making facial expressions during conversation, grimace, or make movements of the face and jaw. Between attacks, the patient is free of symptoms except for fear of an impending attack.

Physical Examination

A characteristic feature of trigeminal neuralgia is the trigger zone, a small area of the skin or orobuccal mucosa that the patient can identify as the point that sets off an attack. Trigger points are generally in the distribution of the nerve branch experiencing the pain. Chewing, talking, facial movement, or touch may elicit a paroxysm. Drafts or cool breezes may also precipitate symptoms. The patient may be reluctant to allow examination of the face for fear of triggering an attack. All cranial nerves should be examined in detail. In secondary trigeminal neuralgia, the corneal reflex may be abnormal.⁵ The remainder of the physical examination, including the neurologic component, yields normal findings.

Diagnostics and Differential Diagnosis

The diagnosis of trigeminal neuralgia is usually made without difficulty from the history and the characteristic manner in which the patient relates the history (the patient is careful not to touch any trigger points or painful areas). Criteria for diagnosis put forth by the International Headache Society include the following³:

• Paroxysms of pain lasting from a fraction of a second to 2 minutes and affecting one or more divisions of the trigeminal nerve without radiation of symptoms

• Pain characterized as at least three events of intense, sharp, superficial, or stabbing nature and precipitated from trigger areas or trigger factors

• No clinically identified neurologic deficit

• Not attributable to another disorder

However, the classic case presentation of trigeminal neuralgia may not always be encountered. Because there are innumerable causes of facial pain, prudence dictates that alternative diagnoses be investigated and that the patient be reexamined at regular intervals. The differential diagnosis should include headache (particularly migraine), acoustic neuroma, trigeminal neuroma, meningioma, aneurysms, acute polyneuropathy, chronic meningitis, other neuralgias, and dental abnormalities. Trigeminal neuralgia is a common cause of pain in multiple sclerosis.

Results of laboratory tests are either normal or noncontributory. If alternative diagnoses are suspected, an autoimmune laboratory panel may be indicated. Trigeminal reflex testing has demonstrated that abnormal reflexes are associated with greater risk of secondary trigeminal neuralgia. Magnetic resonance angiography of the posterior fossa may be undertaken to differentiate vascular abnormalities and to rule out compression from tumor or vessels. Magnetic resonance imaging (MRI) can also corroborate the presence of multiple sclerosis.⁵

Diagnostics

Trigeminal Neuralgia

Diagnosis is based primarily on the patient history and physical findings and requires no initial diagnostic laboratory or imaging studies unless history and physical findings suggest secondary trigeminal neuralgia.

Imaging