Trigeminal neuralgia :An enigma

Author:

Dr. Altaf H Malik

Dept. of Oral and Maxillofacial Surgery,

Govt. Dental College, Srinagar.

Co authors: 

Dr. Ajaz A Shah

Associate Professor and Head,

Dept. of Oral and Maxillofacial Surgery,

Govt. Dental College, Srinagar.

Dr. Suhail Latoo

Lecturer

Department of Oral Pathology and Microbiology,

Govt. Dental College, Srinagar.

Dr. Manzoor Ahmad Malik

J & K Health Services, SDH Banipora

Dr. Rubeena Tabasum

Resident

C.D Hospital, Srinagar.

Dr. Shazia Qadir

Dept. of Oral and Maxillofacial Surgery,

Govt. Dental College, Srinagar.

Definition

            Trigeminal neuralgia (TN -- tic douloureux) is a disorder of the fifth cranial (trigeminal) nerve that causes episodes of intense, stabbing, electric shock-like pain in the areas of the face where the branches of the nerve are distributed - lips, eyes, nose, scalp, forehead, upper jaw, and lower jaw.

Historical note

•  
  • In 1900, in a landmark article, Cushing reported a method of total ablation of the gasserian ganglion to treat TN.
  • In 1912 Osler described TN as follows:
    • In patients with advanced TN, the paroxysms follow one another rapidly without any assignable cause, and in the intervals the patient may never be quite free from pain.
    • They are initiated by almost any form of external stimulus, for example by a draught of air; movement of the facial muscles or tongue while speaking; touching the skin, particularly over those points from which the pain seems to take its origin; and the act of swallowing, especially when the pain involves the mucous membrane field of distribution of the nerve.
    • It is not a self-limited disease. In some instances the neuralgia reaches such a frightful intensity that it renders the patient's life unbearable. In earlier times suicide was not an uncommon consequence.

Pathophysiology:

• Usually no structural lesion is present, although many investigators agree that vascular compression, typically venous or arterial loops at the trigeminal nerve entry into the pons, is critical to the pathogenesis of the idiopathic variety. This compression results in focal trigeminal nerve demyelination.
• Since the exact pathophysiology remains controversial, TN may have either a central and/or peripheral etiology.

CAUSES

It is not always possible to determine what causes trigeminal pain. However, several possibilities exist.

Compression of the nerve root. Compression of the nerve root is nowadays often considered to be the basic cause of classical trigeminal neuralgia. However, other opinions still exist. In this case a small blood vessel pinches the root of the trigeminal nerve. The spasms may be due to the pulsing of the blood vessel, which squeezes the nerve even more.

Damage to the myelin sheath. Damage to the myelin sheath can cause trigeminal pain. This type of damage occurs typically in connection with Multiple Sclerosis (MS). In a somewhat simple way the damage can be seen as a kind of short circuit, the way it is presented in picture 2 (not included here, as I have no scanner, sorry...). Normally, sensations of pain and heat are transmitted by different nerve routes. The myelin sheath of the nerves isolates these routes from each other. If the myelin sheath is damaged, different signals blend together and thus the nerve identifies as pain something that it would, for example, normally feel as a light touch.

Other nerve damage. Accidents, unsuccessful dental work, or various infections can damage the Trigeminal nerve. In this case the damage mechanism is probably similar to that in MS patients. The varicella virus, which causes herpes zoster, can sometimes also cause an intense pain in the trigeminal area. This pain is particularly difficult to treat.

Functional problems. Functional problems in the joints or the bones of the face are often believed to be the cause of atypical facial pain. The jaw bone may squeeze the nerve, and the squeezing is perceived as pain. This pain then causes tension in the muscles of the face, which causes the nerve to be squeezed even more tightly. It can be extremely difficult to break such a vicious circle.

Psychological reasons. 'Psychological reasons' are often mentioned as the underlying cause of atypical face pain. There is no doubt that psychological factors influence the patient's tolerance of pain and how he or she relates to it. Regrettably, however, doctors often use these psychological reasons as a kind of weapon, and do not try to treat the real problem which causes the pain. Chronic pain certainly makes a person angry and depressed; on the other hand there is no reason to assume that anger and depression are the root cause of the pain.

Frequency:

• In the US:
  • According to Penman in 1968, the prevalence of TN is approximately 107 men and 200 women per 1 million people. Mauskop states that approximately 40,000 patients in the US suffer from this condition at any particular time.
  • The incidence is 4-5/100,000.
  • Rushton and Olafson found that approximately 1% of patients with multiple sclerosis (MS) develop TN, whereas Jensen et al stated that 2% of patients with TN have MS.

Mortality/Morbidity:

• TN is not associated with a shortened life. However, the morbidity associated with the chronic and recurrent facial pain can be considerable if the condition is not controlled adequately.

• Individuals may choose to limit activities that precipitate pain, such as chewing, possibly losing weight in extreme circumstances.

• TN may evolve into a chronic pain syndrome, and patients may suffer from depression and related loss of daily functioning.

Race: No racial risk factors have been identified.

Sex: The male-to-female ratio is 2:3.

Age:

• Age of onset typically is 60-70 years; thus, advanced age is a major risk factor.

• Patients who present with the disease when aged 20-40 years are more likely to suffer from a demyelinating lesion in the pons secondary to MS.

• MS and hypertension are the 2 risk factors found in epidemiologic studies.

Criteria :

Classical trigeminal neuralgia fills certain, rather precisely defined criteria.

Spasmodic pain. The pain comes in short spasmodic attacks. It is often described as resembling electric shocks. A typical attack lasts only a few seconds. Several attacks can, however, follow each other within minutes. The pain is, at its worst, completely paralyzing.

Locality. The pain usually appears very locally within the area of the trigeminal nerve and does not radiate into other areas. The pain almost always appears on only one side of the face.

Trigger points. So-called trigger points are typical of trigeminal neuralgia. These are points in the face which, if touched even lightly, will trigger a pain attack. Such points can be located in the lips, on the side of the jaw, underneath the eye, in the eyelid, or anywhere where the trigeminal nerve reaches.

Trigger activities. If an activity causes a trigger-point to be touched, it may start an attack. For example, eating can become almost impossible. Loss of weight is common among those suffering from trigeminal neuralgia. Shaving, applying make-up, and even talking can become difficult. In some cases even a gust of wind can be enough to start an attack. An attack can, however, also start without provocation.

Remissions. So-called remissions, or painless periods, are typical of classical TN. Such a period can begin completely unpredictably and last from a few days to weeks or even months. In this case the pain is completely absent and life does not feel abnormal in any way. Without medical care the pain will, however, usually appear again sooner or later.

CLINICAL

 

History:

• Clinical presentation

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  • TN presents as a stabbing unilateral facial pain that is triggered by chewing or similar activities or by touching affected areas on the face.

•  
  • Patients can localize their pain precisely. The pain is not confined exclusively to one of the 3 divisions of the nerve but more commonly runs along the line dividing either the mandibular and maxillary nerves or the mandibular and ophthalmic portions of the nerve.
    • Of patients, 60% complain of lancinating pain shooting from the corner of the mouth to the angle of the jaw.
    • Jolts of pain from the upper lip or canine teeth to the eye and eyebrow, sparing the orbit itself, are experienced by 30% of patients. This distribution falls between the division of the first and second portions of the nerve.
    • According to Patten, less than 5% of patients experience ophthalmic branch involvement.

•  
  • Strictly unilateral, the disorder affects the right side of the face 5 times more frequently than the left.

•  
  • Pain quality is characteristically severe, paroxysmal, and lancinating.
    • It commences with a sensation of electrical shocks in an affected area, then quickly crescendos 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; hence the term "tic douloureux."

•  
  • The number of attacks may vary from less than one per day, to a dozen or more per hour, up to hundreds per day. Outbursts fully abate between attacks, even when they are severe and frequent.

•  
  • Thus TN is an exception to the rule that nerve injuries typically produce symptoms of constant pain and allodynia. If the pain is particularly frequent, patients may be difficult to examine during the height of an attack.

•  
  • A valuable clue to the diagnosis is the triggering of the pain with certain activities. Patients carefully avoid rubbing the face or shaving a trigger area, in contrast to other facial pain syndromes, in which they massage the face or apply heat or ice.
    • According to Sands, trigger zones, or areas of increased sensitivity, are present in one half of patients and often lie near the nose or mouth.
    • Chewing, talking, smiling, or drinking cold or hot fluids may initiate TN pain. Touching, shaving, brushing teeth, blowing the nose, or encountering cold air from an open automobile window also may elicit pain.

•  
  • In contrast to migrainous pain, persons with TN rarely suffer attacks during sleep, which is a key point in the history.

•  
  • Patients with MS and TN have similar complaints to those with the idiopathic variety, except that they present at a much younger age (often <40 y).
    • Some present with atypical facial pain, without trigger zones, and without the lancinating brief paroxysms of discomfort.
    • As previously noted, TN is not unusual in MS, but it is rarely the first manifestation. Typically it occurs in the advanced stages of MS.

• Natural history and prognosis

•  
  • After an initial attack, the disorder may remit for months or even years. Thereafter the attacks may become more frequent, more easily triggered, more disabling, and may require long-term medication.

•  
  • Patients may find immediate and satisfying relief with one medication, typically carbamazepine. However, over the years, they may require a second or third drug to control breakthrough episodes and finally may need surgical intervention.

•  
  • Simpler, less invasive procedures are well tolerated but usually provide only short-term relief.
    • At this point, further and perhaps more invasive operations may be required, and with these procedures the risk of the disabling adverse effect of anesthesia dolorosa increases.
    • Thus, the long-term prognosis of this disorder varies.

•  
  • According to Fromm et al, some patients may present with pretrigeminal neuralgia syndrome for a period of weeks or even years before developing the customary symptoms of TN. They complain of an unrelenting sinus pain or toothache lasting for hours, triggered by moving the jaw or drinking fluids. Not surprisingly, they first seek dental care. Some find benefit from baclofen or carbamazepine.

Physical:

• In idiopathic TN, neurologic examination findings are normal.

•  
  • Facial sensation, masseter bulk and strength, and corneal reflexes should be intact.

•  
  • No sensory loss is found unless checked immediately after a burst of pain. Any permanent area of numbness excludes the diagnosis.

•  
  • The corneal reflex also should be intact. Loss of this reflex also excludes the diagnosis of idiopathic TN, unless a previous trigeminal nerve section procedure has been performed.

•  
  • The diagnosis of idiopathic TN is tenable only if no physical findings of fifth nerve dysfunction are present.

•  
  • Any jaw or facial weakness or swallowing difficulties suggests another etiology.
  • In patients with MS or a structural lesion and TN, sensory loss often is found on examination.

• Any objective abnormalities in the neurologic examination exclude the diagnosis of idiopathic TN.

Other diagnostic considerations are relevant with TN.

• Other syndromes with paroxysmal lancinating head pain include the less common glossopharyngeal neuralgia (GN) and occipital neuralgia (ON) syndromes.

•  
  • GN causes pain in the tonsillar fossa, posterior pharynx, and ear and may be initiated by coughing, yawning, or swallowing cold liquids.
    • During acute attacks of this disease, which frequently is associated with an underlying pathology, the patient may be unable to speak and tries to avoid moving the lips or tongue.
    • An involuntary startle during an attempt to touch the affected side of the face is diagnostic.

•  
  • ON causes pain in the posterior head region.
    • Thus the distribution easily distinguishes it from TN.
    • Confusion arises only if the patient cannot provide a clear history.

• According to Goadsby and Lipton, paroxysmal hemicrania syndromes typically last only seconds, similar to TN, but occur in and around one eye.

•  
  • Intense unilateral conjunctival injection and lacrimation signal an autonomic component, which further distinguishes this condition.

•  
  • This condition does not respond to carbamazepine.

• Migraine and cluster headaches may produce severe unilateral pain but are not triggered by movement or contact with the face; nor do they respond promptly to carbamazepine.

• According to Turp and Gobetti, atypical face pain usually extends beyond the distribution of the fifth cranial nerve, rarely is triggered, and presents with a steady unrelenting discomfo