Introduction

The trigeminal nerve (also known as the nervus trigeminus) is one of the main nerves from the brain that provides sensation to the face. Trigeminal neuralgia is when there is pain in the regions of the face that are supplied by the trigeminal nerve. Recurrent, evocable, unilateral, short, electric, shock-like pains with abrupt start and cessation that affect one or more trigeminal nerve divisions are the characteristic symptoms of trigeminal neuralgia(TN).¹ This means that the shock-like pains mainly affect one side of the face, starting for no clear reason and sometimes persisting.

Definition

According to the beta version of the 3rd edition of the International Classification of Headache Disorders (ICHD-3 Beta), recurrent unilateral short electric shock-like pain with abrupt onset and cessation is the hallmark of trigeminal neuralgia (TN). The pain is confined to one or more branches of the trigeminal nerve and is brought on by harmless sensory stimulation. TN is classified as secondary TN (STN) or classical TN (CTN). The classical form is caused by the trigeminal nerve being pinched, whereas secondary TN can be brought on by another known cause, such as multiple sclerosis or a lesion that occupies space, like a tumour, cerebral aneurysm or megadolicho basilar artery.²

Epidemiology

It is common for TN to be insufficiently diagnosed or misdiagnosed. Studies have found varying incidences ranging from 4.3 to 27 new cases per 100,000 individuals per year.^3,4 Women experience a greater incidence rate, increasing with age.³ According to population-based research, the lifetime prevalence was estimated to be 0.16 to0.3%.^5,6 Although the age of onset can vary from early infancy to old age, it typically occurs between 43 and 53 years of age in classical TN and 43 years in secondary TN.^7,8 Secondary TN accounted for 14 to 20% of TN patients in studies based on tertiary care.

Who is most at risk of having trigeminal neuralgia?

According to US data, women were shown to have a higher risk of developing trigeminal neuralgia than men. However, this association did not hold true when accounting for the fact that women live longer than men.³ Multiple sclerosis and trigeminal neuralgia have the strongest correlation, according to data from both diseases and epidemiological studies.⁹ Additionally, there may be a correlation with hypertension (high blood pressure) and stroke.¹⁰ However, given the comparable epidemiology of hypertension and other degenerative diseases, this correlation may just be the result of chance.

What causes trigeminal neuralgia?

Classical trigeminal neuralgia may result from compression or irritation of the trigeminal nerve by blood vessels or tumour tissue close to the brainstem's origin, or the "root entry zone". Secondary trigeminal neuralgia is caused by another condition like multiple sclerosis or autoimmune conditions, which can affect the trigeminal nerve.^10,12 They can cause demyelination (which is when nerves wrap some of the fat around their stem, making them work more slowly), damage to the protective sheath of the neuron and changes to the nociceptive (pain) system.^13,14

Diagnosis

When diagnosing TN, a complete and accurate patient history is crucial because the diagnosis is partially exclusionary and based on particular clinical symptoms. However, additional testing may be necessary to further define the exact aetiology (cause of the pain or the condition).¹³

The hallmark of trigeminal neuralgia is excruciating shooting agony. This might be triggered by various stimuli, such as heat, cold, draft, eating, shaving and tooth brushing.¹⁵

 According to the International Headache Society, trigeminal neuralgia meets the following diagnostic criteria:

1. Paroxysmal pain in one or more trigeminal nerve branches, lasting anywhere from a few seconds to two minutes
2. Pain is characterised by at least one of the following: stabbing, acute, sharp, or superficial, emerging from the region where the trigger or trigger components were.
3. Symptoms are not explained by other neurological conditions
4. Seizures are not a symptom of other illnesses
5. The trigeminal nerve's maxillary and mandibular branches are where the pain typically manifests itself¹⁵

Following a diagnosis of trigeminal neuralgia, the patient should get an MRI to rule out other conditions that could be causing secondary trigeminal neuralgia, such as multiple sclerosis or tumours. If there is a possibility of nervus trigeminus compression in the fossa cranial posterior (if the trigeminal nerve is pinched inside the skull), an MRI scan may be performed. Occasionally, the sensitivity of the MRI scan allows for the detection of blood vessels that have compressed the nervus trigeminus. There is debate over the involvement of venous compression in the aetiology of trigeminal neuralgia. Interestingly, one-third of asymptomatic patients have compressed blood vessels visible on MRI scans.^18,19 

Differential diagnosis

A differential diagnosis is when other conditions that cause similar symptoms are considered. Unilateral, episodic pain may be explained by other conditions. Diseases of the teeth, temporomandibular joint, orbital cellulitis, trauma, glaucoma, facial trauma, skeletal fractures, tumours of the facial bones or trigeminal nerve, giant cell arteritis and joint disorders can cause similar symptoms. Facial discomfort can be brought on by trigeminal autonomic cephalgias (such as paroxysmal hemicrania and cluster headache), Tolosa-Hunt syndrome ( inflammation in or around the cavernous sinus), and various primary headache syndromes (such as migraine and tension-type headache).¹⁹

It is important to evaluate any such pain as possibly being indicative of neuralgia. Trigeminal autonomic cephalalgia is the other main category of diseases to take into consideration. The primary characteristic that sets these pains apart is that they typically affect the trigeminal nerve's first division rather than its second or third divisions. Patients who suffer from any of these ailments may experience lengthier pain episodes.¹⁹ There may be a greater number of episodes and no refractory period (a period where the pain subsides).

Patients with trigeminal neuralgia prefer to remain still, whereas those with these disorders are frequently restless and disturbed. Autonomic symptoms that patients may experience include tears, eye redness, miosis (constriction of the pupils), swelling of the upper eyelids, stuffy nose or rhinorrhea (runny nose), facial redness and a fullness in the ear. Surgery is not necessary for these patients.²⁰ Younger patients get trigeminal neuralgia less commonly. Multiple sclerosis needs to be considered when a differential diagnosis is made, particularly when there are bilateral symptoms.²⁰ 

Treatment 

Conservative treatments

Antiepileptic medications have been the cornerstone of treatment for trigeminal neuralgia since 1860. The discovery of carbamazepine in 1962 completely changed the way this illness was treated, and it has since remained the gold standard.²² Rehydration and the titration of antiepileptic medications may require in-hospital treatment during acute exacerbations.

 The best drugs for long-term therapy are still carbamazepine (200 to 1200 mg per day) or oxcarbazepine (300 to 1800 mg per day), particularly in the early stages of TN.

 In the event that these medications stop working or have poor tolerability, alternative medications should be explored. When first-line medications are ineffective or intolerable, lamotrigine, gabapentin, botulinum toxin type A, pregabalin, baclofen, and phenytoin may be used alone or in combination with carbamazepine or oxcarbazepine.²⁰ However, this is based on little evidence.

Patients should be instructed to gradually increase and reduce dosages over a few days. The managing physician should continue to make sure the patient is informed about all available neurosurgical alternatives and is capable of making an informed treatment decision. If no other underlying cause is identified, up to 10% of patients may not respond to these medications, yet still be eligible for interventional therapy.

Interventional treatments

If medical treatment is ineffective or you experience too many negative side effects, surgical procedures may be performed:

• Surgical microvascular decompression (MVD)
• Stereotactic radiation therapy, gamma knife
• Percutaneous balloon micro compression
• Percutaneous glycerol rhizolysis
• Percutaneous radiofrequency (RF) treatment of the Gasserian ganglion^19,20,23 

Biochemical investigations

Trigeminal neuralgia medications, especially antiepileptic medications, have a history of side effects, including hyponatraemia (low blood sodium), increased liver transaminases, and decreased white blood cell counts. Thus, to monitor for possible medication toxicity over time, a complete blood count at baseline with differential, serum electrolytes, and liver function tests may be required, depending on the anticipated course of therapy. This means that blood tests need to be carried out to check that the medications are not having a toxic effect. It is not advised to regularly monitor blood tests unless there is a clinical indication. The National Institute for Health and Care Excellence (NICE) suggests that every two to five years, patients taking enzyme-inducing medications should have a complete blood count, as well as measurements of electrolytes, liver enzymes, and vitamin D levels, in addition to other tests of bone metabolism (such as serum calcium and alkaline phosphatase).²¹

Summary

Trigeminal neuralgia (TN) is a chronic pain disorder affecting one or more branches of the trigeminal nerve, marked by sudden, unilateral, electric shock-like facial pain triggered by light stimuli such as eating or brushing teeth. It is classified as classical TN (usually due to vascular compression) or secondary TN (caused by conditions like multiple sclerosis or tumours).

Epidemiology & risk factors

• Incidence: 4.3–27 per 100,000 annually
• More common in women and older adults
• Strongly associated with multiple sclerosis; possible links to hypertension and stroke

Diagnosis

• Based on clinical history and ICHD-3 criteria (brief, unilateral, stabbing pain not explained by other conditions)
• MRI is recommended to rule out secondary causes
• Differential diagnoses include dental disease, TMJ disorders, headaches, and trigeminal autonomic cephalalgias

Treatment

• First-line: Carbamazepine or oxcarbazepine; alternatives include lamotrigine, gabapentin, pregabalin, baclofen, phenytoin, and botulinum toxin A.
• Monitoring: Blood tests may be needed for long-term antiepileptic therapy to check for side effects (e.g., hyponatremia, liver toxicity).
• Interventional options (for refractory cases): Microvascular decompression, stereotactic radiosurgery (Gamma Knife), percutaneous balloon compression, glycerol rhizolysis, or radiofrequency ablation.

Key point

Early and accurate diagnosis is essential to distinguish TN from other facial pain disorders. Medical therapy is the first choice, but surgical or interventional procedures are effective alternatives when drugs fail or cause intolerable side effects.