Trigeminal Neuralgia

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Introduction

Trigeminal Neuralgia (TN), also known as "Tic D", is afacial pain syndrome. It is characterized by unilateral facial pain following the sensory distribution of cranial nerve V, the Trigeminal Nerve. Most commonly the pain radiates to the mandibular or maxillary regions (in 35% of paitients). In some cases it is accompanied by a brief facial spasm or tic.

Clinically Relevant Anatomy

The trigeminal nerve (the fifth cranial nerve, or simply CN V) is the nerve responsible for sensation in the face, and control of motor functions such as biting and chewing.

 Its name ("trigeminal" = tri- or three, and -geminus or twin, or thrice twinned) derives from the fact that it has three major branches: the ophthalmic nerve (V1) 1st branch; the maxillary nerve (V2) 2nd branch, and the mandibular nerve (V3) 3rd branch. The ophthalmic and maxillary nerves are purely sensory. The mandibular nerve has both cutaneous and motor functions, the motor supply being tothe muscles of mastication. which include temporalis and masseter.

 

Mechanism of Injury / Pathological Process

Usually, no structural lesion is present (85%), although many investigators agree that vascular compression (,ie. venous or arterial loops at the trigeminal nerve entry into the pons) is implicated in the pathogenesis of the idiopathic variety. This compression results in focal trigeminal nerve demyelination. The etiology is labeled idiopathic by default, and is then categorized as "classic trigeminal neuralgia"

Microanatomic small and large fibre damage in the nerve, essentially demyelination  leads to ephaptic transmission, in which action potentials jump from one fiber to another.

Epidemiology

Recent estimates suggest the prevalence is approximately 1.5 cases per 10,000 population, with an incidence of approximately 15,000 cases per year.

Age

In 90% of patients, the disease begins after age 40 years, most often between 60-70 years.

Gender

Woman are  affected more than men, with figures quoted between  3:2 to 2:1. 

Multiple Sclerosis

Rushton and Olafson found that approximately 1% of patients with multiple sclerosis (MS) develop TN,

Jensen et al noted that 2% of patients with trigeminal neuralgia have multiple sclerosis

Patients with both conditions frequently have bilateral trigeminal neuralgia.

Clinical Presentation

Trigeminal neuralgia (TN) presents as a stabbing unilateral facial pain that is usually triggered by chewing activities, or by touching affected areas on the face.

Area of pain

60% of patients with TN present with lancinating pain shooting from the corner of the mouth to the angle of the jaw

30% experience jolts of pain from the upper lip or canine teeth to the eye and eyebrow, sparing the orbit itself—this distribution falls between the division of the first and second portions of the nerve.

According to Patten, fewer than 5% of patients experience ophthalmic branch involvement.

Characteristic Descriptors of pain

The pain quality is  severe, paroxysmal, and lancinating.

It usually starts with a sensation of electrical shocks, then quickly increases in less than 20 seconds to an excruciating discomfort felt deep in the face, often contorting the patient's expression. The pain then begins to fade within seconds, only to give way to a burning ache lasting seconds to minutes. During attacks, patients may grimace, wince, or make an aversive head movement, as if trying to escape the pain, thus producing an obvious movement, or tic; hence the term "tic douloureux."

Fquency of pain

The number of attacks may vary from less than 1 per day, to hundreds per day.

Outbursts fully abate between attacks, even when they are severe and frequent.

Pain Triggers

A common feature of TN is that the pain is triggered by touching the painful area of the face, as well as activities such as shaving, rubbing, brushing teeth, moving face to talk, cold wind on the face, etc.

Studies suggest that  trigger zones, or areas of increased sensitivity, are present in one half of patients and often lie near the nose or mouth.

Diagnosis and Classification

The International Headache Society (IHS) have published strict criteria for TN:

A - Paroxysmal attacks of pain lasting from a fraction of a second to 2 minutes, affecting 1 or more divisions of the trigeminal nerve and fulfilling criteria B and C
B - Pain has at least 1 of the following characteristics: (1) intense, sharp, superficial or stabbing; or (2) precipitated from trigger areas or by trigger factors
C - Attacks stereotyped in the individual patient
D - No clinically evident neurologic deficit
E - Not attributed to another disorder

No laboratory, electrophysiologic, or radiologic testing is routinely indicated for the diagnosis of trigeminal neuralgia (TN), as patients with characteristic history and normal neurologic examination may be treated without further investigation.

The diagnosis of TN is almost entirely based on the patient's history and in most cases  no specific laboratory tests are needed.

MRI scanning is often indicated simply to exclude other causes of the pain, such as pressure on the trigeminal nerve from Acoustic Neuroma.

Outcome Measures

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Management / Interventions

Medical Management

A range of anti-epileptic drugs have proved to be useful in management of TN, with carbamazepine in particular having a large number of studies demonstrating efficacy.

Non anti-epileptic drugs can also be prescribed, often in conjunction with carbamazepine.

Surgical Management

Studies suggest that approximately 25% of TN patients go on to require surgery as their condition worsens over years, and the drug management becomes less effective.  Microvascular decompression and radiofrequency thermorhizotomy are the most common surgical procedures employed in these cases.

Differential Diagnosis

The main diffential diagnoses for TN are:

• Atypical facial pain - this common facial pain is less intense than TN, described as a dull or throbbing ache which lasts for minutes to hours
• Migraine can cause severe unilateral facial pain
• As can Cluster headaches

Key Evidence

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Resources

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Case Studies

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Recent Related Research (from Pubmed)

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References

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