What is the main cause of trigeminal neuralgia?

What is the main cause of trigeminal neuralgia? Trigeminal Neuralgia (TN or TGN) is a chronic? pain? disorder that affects the trigeminal nerve. There are two main types: typical and atypical trigeminal neuralgia. The typical form results in episodes of severe, sudden, shock-like pain? in one side of the face that lasts for seconds to a few minutes. Groups of these episodes can occur over a few hours. The atypical form results in a constant burning pain? that is less severe. Episodes may be triggered by any touch to the face. Both forms may occur in the same person. It is one of the most painful conditions and can result in depression

Trigeminal neuralgia is an uncommon disorder characterized by recurrent attacks of lancinating pain? in the trigeminal nerve distribution. Typically, brief attacks are triggered by talking, chewing, teeth brushing, shaving, a light touch, or even a cool breeze. The pain is nearly always unilateral, and it may occur repeatedly throughout the day. The diagnosis? is typically determined clinically, although imaging studies or referral for specialized testing may be necessary to rule out other diseases. Accurate and prompt diagnosis is important because the pain of trigeminal neuralgia can be severe.[Rx]

Function I

The trigeminal nerve (cranial nerve V) is so named because it has three (tri) branches responsible for face sensation; one branch also regulates chewing.

• The ophthalmic branch (V₁) – is responsible for sensation from the scalp, forehead, upper eyelid and tip of the nose.
• The maxillary branch (V₂) – sensation covers the lower eyelid, the side of the nose, the upper lip and cheek, and the upper teeth and gums.
• The mandibular branch (V₃) – is responsible for sensation than of the lower teeth and gums, lower lip, chin, jaw, and part of the ear. It is also responsible for supplying the muscles involved with chewing (mastication), those muscles involved with chewing.

Causes of Atypical Trigeminal Neuralgia

In trigeminal neuralgia, also called tic douloureux, the trigeminal nerve’s function is disrupted. Usually, the problem is contact between a normal blood vessel — in this case, an artery or a vein — and the trigeminal nerve at the base of your brain. This contact puts pressure on the nerve and causes it to malfunction.

Trigeminal neuralgia can occur as a result of aging, or it can be related to multiple sclerosis? or a similar disorder that damages the myelin sheath protecting certain nerves. Less commonly, trigeminal neuralgia can be caused by a tumor compressing the trigeminal nerve.

• Most cases of trigeminal neuralgia are believed to be caused by blood vessels pressing on the root of the trigeminal nerve. This is said to make the nerve transmit pain? signals which are experienced as the stabbing pains of trigeminal neuralgia. However, experts are not completely sure of the cause. Pressure on the trigeminal nerve may also be caused by a tumor or multiple sclerosis?.

Below is a list of known and suspected causes

• A blood vessel presses – against the root of the trigeminal nerve.
• Multiple sclerosis? – due to demyelinization of the nerve. Trigeminal neuralgia typically appears in the advanced stages of multiple sclerosis?.
• A tumor presses –  against the trigeminal nerve. This is a rare cause.

• Physical damage to the nerve – this may be the result of injury, a dental or surgical procedure, or infection?.

Family history (genes, inherited) – 4.1% of patients with unilateral trigeminal neuralgia (affects just one side of the face) and 17% of those with bilateral trigeminal neuralgia (affects both sides of the face) have close relatives with the disorder. Compared to a 1 in 15,000 risk in the general population, 4.1% and 17% indicate that inheritance is probably a factor

Triggers of Atypical Trigeminal Neuralgia

A variety of triggers may set off the pain? of trigeminal neuralgia, including:

• Shaving
• Touching your face
• Eating
• Drinking
• Brushing your teeth
• Talking
• Putting on makeup
• Encountering a breeze
• Smiling
• Washing your face

Symptoms of Atypical Trigeminal Neuralgia

TN presents as attacks of stabbing unilateral facial pain?, most often on the right side of the face. The number of attacks may vary from less than 1 per day to 12 or more per hour and up to hundreds per day.

Triggers of pain? attacks include the following

• Chewing, talking, or smiling
• Drinking cold or hot fluids
• Touching, shaving, brushing teeth, blowing the nose
• Encountering cold air from an open automobile window

Pain? localization is as follows

• Patients can localize their pain? precisely
• The pain? commonly runs along the line dividing either the mandibular and maxillary nerves or the maxillary and ophthalmic portions of the nerve
• In 60% of cases, the pain? shoots from the corner of the mouth to the angle of the jaw
• In 30%, pain? jolts from the upper lip or canine teeth to the eye and eyebrow, sparing the orbit itself
• In less than 5% of cases, pain? involves the ophthalmic branch of the facial nerve
• 

The pain? has the following qualities

• Characteristically severe, paroxysmal, and lancinating
• Commences with a sensation of electrical shocks in the affected area
• Crescendos in less than 20 seconds to an excruciating discomfort felt deep in the face, often contorting the patient’s expression
• Begins to fade within seconds, only to give way to a burning ache lasting seconds to minutes
• Pain? fully abates between attacks, even when they are severe and frequent
• Attacks may provoke patients to 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”

Other diagnostic clues are as follows

• 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
• Many patients try to hold their face still while talking, to avoid precipitating an attack
• In contrast to migrainous pain?, attacks of TN rarely occur during sleep

Diagnosis? of Trigeminal Neuralgia

• No laboratory, electrophysiologic, or radiologic testing is routinely indicated for the diagnosis? of TN, as patients with a characteristic history and normal neurologic examination may be treated without further workup.

Strict criteria for TN as defined by the International pain? in the head or upper neck. সহজ বাংলা: মাথাব্যথা।" data-rx-term="headache" data-rx-definition="Headache means pain in the head or upper neck. সহজ বাংলা: মাথাব্যথা।">Headache? Society (IHS) are as follows :

• 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

IHS criteria for symptomatic TN vary slightly from the strict criteria and include the following 

• A – Paroxysmal attacks of pain? lasting from a fraction of a second to 2 minutes, with or without persistence of aching between paroxysms, 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 – A causative lesion?, other than vascular compression, demonstrated by special investigations and/or posterior fossa exploration

A blood count and liver function tests are required if therapy with carbamazepine is contemplated. Oxcarbazepine can cause hyponatremia, so the serum sodium level should be measured after the institution of therapy.

References