Trigeminal Neuropathy

Overview

The most prevalent neuropathic pain affecting the craniofacial region is trigeminal neuralgia (TN), often known as tic douloureux. It is distinguished by abrupt, transient, typically unilateral severe recurring bouts of stabbing pain in the distribution of one or more trigeminal nerve branches.

What is trigeminal neuropathy?

Trigeminal neuropathy (TN), also known as tic douloureux, is a chronic pain syndrome affecting the trigeminal or 5th cranial nerve, which is one of the most extensively distributed nerves in the brain. The condition known as TN is a kind of neuropathic pain (pain associated with nerve injury or nerve lesion.) The "classic" type of the condition (known as "Type 1" or TN1) causes intense, intermittent, abrupt searing or shock-like face pain that can last anywhere from a few seconds to two minutes each episode. These attacks can come in rapid succession, with volleys lasting up to two hours. The "atypical" type of the illness (known as "Type 2" or TN2) is distinguished by persistent aching, burning, and stabbing pain that is milder than Type 1. The trigeminal nerve is one of 12 nerve pairs that connect to the brain. The nerve contains three branches that carry sensations to the brain from the top, middle, and lower parts of the face, as well as the mouth cavity. The ophthalmic, or top, branch is responsible for providing sensation to the majority of the scalp, forehead, and front of the head. The maxillary, or middle, branch stimulates the face, upper jaw, top lip, teeth and gums, and nasal side. The lower, or mandibular, branch provides nerves to the lower jaw, teeth and gums, and bottom lip. The condition can damage more than one nerve branch. Rarely, both sides of the face may be afflicted at separate periods in a person, and even more rarely, both sides of the face may be affected at the same time (called bilateral TN). 

Epidemiology

Trigeminal neuralgia has a frequency of 0.1 to 0.2 per thousand persons and an annual incidence of 4 to 20 cases per 100,000 people. The female to male ratio is around 3 to 2. While it is frequent beyond the age of 50, it is uncommon in young people and extremely rare in children. The right side of the face was found to be more frequently implicated.

What causes trigeminal neuropathy?

Trigeminal neuralgia's specific cause is unclear. The vast majority of cases are classified as idiopathic, although many are linked to vascular compression of the trigeminal nerve near its exit from the brainstem by an abnormal loop of an artery or vein. A small percentage of instances are caused by illnesses such as multiple sclerosis or nerve compression caused by a tumor. Focal arachnoid thickening, adhesion, traction, tethering or torsion, fibrous ring around the root, cerebellopontine angle tumors, brain stem infarction, aneurysm, and arteriovenous malformation are all unusual causes of trigeminal neuralgia.

• The Vascular Theory - Trigeminal neuralgia is commonly thought to be produced by vascular contact at the root entrance zone; however, TN may also be induced by contact at a transition zone between the central and peripheral myelin. According to reports, the superior cerebellar artery is the most often affected artery in this illness, accounting for 75% to 80% of TN instances. TN can be caused by a persistent primitive trigeminal artery variety, an abnormality between the carotid and basilar arteries, or aneurysms of the persistent primitive trigeminal artery, vertebrobasilar dolichoectasia. Sharper trigeminal-pontine angle cisterns and smaller cerebellopontine angle cisterns may make neurovascular compression easier (NVC).
• Extracranial Factors - Perineural spread of head and neck malignancies, most often squamous cell carcinoma, adenoid cystic carcinoma, lymphoma, melanoma, and sarcoma, is the most prevalent extracranial cause of trigeminal neuralgia.

Pathophysiology

Exact pathophysiology is still debated. According to one idea, persistent nerve compression can cause localized demyelination at the trigeminal nerve's entrance zone, atrophy or hypertrophy of peripheral axons, and damage to Schwann cells and peripheral myelin.  Demyelinated lesions can result in ectopic impulse production, which can lead to ephaptic transmission. Light tactile stimulation of face trigger zones might cause painful attacks due to ephaptic cross-talk between fibers mediating light touch and those engaged in pain creation.

What are the signs and symptoms of trigeminal neuropathy?

Trigeminal neuropathy causes episodes of spontaneous or triggered intense facial pain that last for a short period of time (a few seconds to two minutes). Pain may feel like stabbing, electric shocks, burning, pressing, crushing, shooting, migraine-like, piercing, prickling, or a combination of these. Pain is almost often unilateral and just occasionally bilateral.

The distribution of TN discomfort may occur in one or more of the three divisions: ophthalmic (V1), maxillary (V2), and mandibular (V3) (V3). V2 is the most often engaged region, followed by V3, and then V1. Pain episodes are often triggered by the activation of trigger points in the area supplied by the trigeminal nerve. Touching the face, cleaning one's teeth, conversing, and eating are all examples of stimulation. Each pain episode can be followed by a refractory phase that might range from a few seconds to several minutes. Patients who experience frequent episodes may avoid talking or eating. This might have a negative impact on the patients' quality of life and mental health.

Autonomic symptoms (e.g., modest lacrimation without conjunctival injection) may occur in conjunction with V1 trigeminal TN episodes. This is in stark contrast to SUNCT episodes, which are usually followed by lacrimation and conjunctival injection on the affected side from the commencement of symptoms.

Criteria and Diagnosis

• At least three episodes of face discomfort, most of which were unilateral
• There is no radiation outside the trigeminal distribution and it occurs in one or more divisions of the trigeminal nerve.
• It can last anywhere from a fraction of a second and over two minutes.
• Excruciating agony
• In terms of quality, it might be electric shock-like, shooting, sharp, or stabbing.
• Innocuous stimuli inside the afflicted trigeminal division caused it.

Who is significantly affected?

Trigeminal neuralgia is most common in adults over the age of 50, but it can develop at any age, including infancy. When TN occurs in young adults, the likelihood that it is caused by multiple sclerosis increases. The condition affects around 12 people out of every 100,000 people each year, and it affects women more than males.

How is trigeminal neuropathy diagnosed?

The diagnosis of TN is mostly based on the individual's history and description of symptoms, as well as the findings of physical and neurological testing. Before TN is diagnosed, other conditions that cause face discomfort should be checked out. Post-herpetic neuralgia (nerve pain following a shingles outbreak), cluster headaches, and temporomandibular joint disease are all conditions that induce face discomfort (TMJ, which causes pain and dysfunction in the jaw joint and muscles that control jaw movement). Since of overlapping symptoms and the wide number of illnesses that can cause face pain, gaining a precise diagnosis is challenging; yet, determining the origin of the pain is critical because therapies for different types of pain may differ.

Most persons with TN will ultimately get an MRI scan to rule out a tumor or multiple sclerosis as the source of their discomfort. A blood artery squeezing the nerve may or may not be visible on this imaging. Special MRI imaging approaches can detect the existence and degree of nerve compression by a blood artery.

A favorable response to a short course of antiseizure medication may support a diagnosis of classic trigeminal neuralgia. TN2 is a more complex and challenging diagnosis, although it is supported by a favorable response to modest doses of tricyclic antidepressant drugs (such as amitriptyline and nortriptyline), as with other neuropathic pain diagnoses.

How is trigeminal neuropathy treated?

Medicines, surgery, and alternative therapies are among the treatment possibilities.

Medications

Anticonvulsant medications, which are used to stop nerve firing, are typically useful in treating TN1 but are frequently ineffective in treating TN2. Carbamazepine, oxcarbazepine, topiramate, gabapentin, pregabalin, clonazepam, phenytoin, lamotrigine, and valproic acid are examples of these medications.

Pain can be treated with tricyclic antidepressants such as amitriptyline or nortriptyline. Common analgesics and opioids are not typically effective in treating the acute, persistent pain produced by TN1, while opioids can benefit some people with TN2. If medicine fails to reduce pain or causes unbearable side effects such as cognitive problems, memory loss, excessive tiredness, bone marrow suppression, or allergies, surgical therapy may be recommended. Because TN is a progressive condition that frequently develops resistant to therapy over time, people frequently seek surgical therapy.

Surgery

Depending on the nature of the pain, the individual's preference, physical health, blood pressure, and previous surgeries, the presence of multiple sclerosis, and the distribution of trigeminal nerve involvement (particularly when the upper/ophthalmic branch is involved), several neurosurgical procedures are available to treat TN. Some operations are performed as outpatients, while others may need a more difficult surgery under general anesthesia. Many of these surgeries will cause some degree of facial numbness, and TN will frequently recur even if the operation is initially effective. Other hazards of surgery include hearing loss, balance issues, cerebrospinal fluid leakage (the fluid that bathes the brain and spinal cord), infection, anesthesia dolorosa (a combination of surface numbness and deep searing agony), and stroke, though the latter is uncommon.

A rhizotomy (rhizolysis) is a pain-blocking technique that involves damaging nerve fibers. A rhizotomy for TN invariably results in sensory loss and face numbness. There are several types of rhizotomy offered to treat trigeminal neuralgia:

• Balloon compression works by damaging the insulation on neurons responsible for the sense of light touch on the face. The surgery is carried out in an operating room while the patient is sedated. A cannula is introduced through the cheek and directed to the location where one branch of the trigeminal nerve exits the base of the skull. A soft catheter with a balloon tip is inserted through the cannula and inflated to push a section of the nerve against the hard edge of the brain covering (the dura) and the skull. After roughly a minute, the balloon is deflated and the catheter and cannula are withdrawn. Balloon compression is often performed as an outpatient surgery, although the patient may be detained in the hospital overnight on occasion. Pain alleviation normally lasts between one and two years.
• Glycerol injection is also often performed as an outpatient operation in which the patient is anesthetized with intravenous medication. A small needle is directed through the aperture in the base of the skull where the third division of the trigeminal nerve (mandibular) emerges by passing it through the cheek, adjacent to the mouth. The needle is inserted into the spinal fluid pocket (cistern) that surrounds the trigeminal nerve center (or ganglion, the central part of the nerve from which the nerve impulses are transmitted to the brain). Because glycerol is heavier than spinal fluid and will linger in the spinal fluid around the ganglion, the operation is conducted with the patient sitting up. The glycerol injection bathes the ganglion and destroys the trigeminal nerve insulation. This type of rhizotomy is likely to cause pain to return after a year to two years. The operation, however, can be performed numerous times.
• Outpatient radiofrequency thermal lesioning (also known as "RF Ablation" or "RF Lesion") is the most common procedure. Anesthesia is administered to the patient, and a hollow needle is inserted through the cheek into the same hole at the base of the skull where the balloon compression and glycerol injections are administered. The person is temporarily woken, and a little electrical current is sent through the needle, generating tingling in the nerve region where the needle points lie. The individual is anesthetized after the needle is positioned such that the tingling occurs in the location of TN discomfort, and the nerve area is progressively heated with an electrode, damaging the nerve fibers. After then, the electrode and needle are withdrawn, and the patient is woken. The technique can be continued until the desired level of sensory loss is achieved, which is generally a blunting of acute feeling while preserving touch. Approximately half of the participants get recurrent symptoms three to four years after RF lesioning. The production of additional numbness can prolong pain relief even farther, but it also increases the hazards of anesthesia dolorosa.
• Stereotactic radiosurgery (Gamma Knife, Cyberknife) directs highly targeted beams of radiation at the location where the trigeminal nerve exits the brainstem using computer imagery. This results in the gradual creation of a lesion on the nerve, interfering with the transmission of sensory impulses to the brain. People normally leave the hospital the same day or the next day after treatment, although they will not get pain relief for several weeks (or occasionally months) after the surgery. According to the International RadioSurgery Association, between 50 and 78 percent of persons with TN who have Gamma Knife radiosurgery find "excellent" pain reduction within a few weeks of the treatment. Almost half of those who were effectively treated have pain recurrence within three years.
• Microvascular decompression (MVD) is the most invasive of all TN operations, but it also has the lowest risk of pain recurrence. Approximately half of those who get MVD for TN will develop recurrence pain within 12 to 15 years. A tiny hole through the mastoid bone behind the ear is required for this inpatient surgery, which is performed under general anesthesia. While looking at the trigeminal nerve using a microscope or endoscope, the surgeon removes the vessel (typically an artery) that is crushing the nerve and inserts a soft cushion between the nerve and the vessel. Unlike rhizotomies, the purpose of this procedure is not to cause facial numbness. Following the operation, most people spend several days in the hospital recovering, you will usually need to rest for many weeks following the treatment.

If no vessel is detected to be pushing on the trigeminal nerve, a neurectomy (also known as partial nerve section) may be done around the nerve's entry point at the brain stem during an attempted microvascular decompression. Neurectomies can also be conducted by severing the trigeminal nerve's superficial branches in the face. A neurectomy performed during microvascular decompression will result in more long-term numbness in the region of the face supplied by the nerve or nerve branch that is severed. However, if the procedure is performed on the face, the nerve may regenerate and feeling may return over time. There is a risk of anesthesia dolorosa with neurectomy.

Surgical therapy for TN2 is typically more difficult than treatment for TN1, especially if vascular compression is not discovered in brain imaging prior to a proposed surgery. Many neurosurgeons advise against using MVD or rhizotomy in patients with TN2 symptoms over TN1, unless vascular compression is established. MVD for TN2 is similarly less effective than MVD for TN1.

Alternative methods

Some people treat trigeminal neuralgia with complementary treatments, generally in conjunction with medication. These treatments have different degrees of effectiveness. Some people believe that low-impact exercise, yoga, creative visualization, scent therapy, or meditation might help them feel better. Acupuncture, upper cervical chiropractic, biofeedback, vitamin treatment, and nutritional therapy are other choices. Some persons experience some pain reduction after receiving botulinum toxin injections to disrupt sensory nerve activity.

Chronic TN pain may be quite lonely and upsetting for the sufferer. Depression and sleep disruption, on the other hand, may make people more prone to pain and suffering. A psychiatrist or psychologist may provide supportive counseling or therapy to some people. There is little evidence that TN is psychogenic or caused by depression, and people with TN require good medical or surgical pain relief.

Differential Diagnosis

Due to the fact that trigeminal neuralgia is predominantly unilateral, the most common differential diagnoses include dental pain (e.g., cavities, broken tooth, chronic periodontitis), temporomandibular dysfunction, glossopharyngeal neuralgia, postherpetic neuralgia, and SUNCT.

Prognosis

The majority of patients respond effectively to medicines. If medication therapy fails or is not tolerated, surgical options may be considered. [4] Recurrence of pain is frequent, with the majority of relapses happening within the first two years. After MVD, the predicted yearly recurrence rate is 3.5%.

Female sex, left-sided discomfort, and symptoms lasting more than 11 years have all been identified as risk factors for recurrence following MVD.

Conclusion

Trigeminal neuralgia is characterized by abrupt, intense face discomfort. It is frequently characterized as a sudden shooting pain or an electric shock in the jaw, teeth, or gums. It frequently comes in quick, unexpected bursts that last anywhere from a few seconds to roughly 2 minutes. The attacks come to an abrupt halt. Trigeminal neuralgia often affects only one side of the face, with pain felt in the bottom half of the face. Pain can occasionally affect both sides of the face, albeit not always at the same moment.

People suffering from the illness may endure pain episodes on a daily, weekly, or monthly basis. Attacks might occur hundreds of times each day in extreme situations.