Introduction

Trigeminal neuralgia is a rare, chronic pain condition characterised by recurrent, short-lasting, electric shock-like pain affecting one or more trigeminal nerve divisions to one side of the face (TN). Pain is often severe and triggered by mild sensory input, such as touch. Diagnosis is based on clinical history and examination and may involve an MRI scan. Treatment involves anti-epileptic medications and surgical interventions, which are usually effective in providing relief.¹

What is trigeminal neuralgia?

According to the International Classification of Headache Disorders (ICHD-3 Beta), trigeminal neuralgia (TN) is characterised by recurrent, unilateral (one-sided),  electric shock-like pain, typically lasting seconds to minutes.² Pain is confined to one of the three branches of the trigeminal nerve, the ophthalmic, maxillary and mandibular nerves, which stem from the trigeminal nerve and provide sensory and motor information to the face.³ This pain is triggered by light stimuli such as touch, heat, cold, draft, eating, shaving, and tooth brushing.^{1, 4}

Trigeminal neuralgia is classified as:

• Classical TN (CTN): This is due to compression of the trigeminal nerve by a vascular structure such as the megadolicho basilar artery, or the superior cerebellar artery, which branches off from it
• Secondary TN (STN): This is due to a neurological disorder, such as multiple sclerosis (MS),  or a space-occupying lesion,  such as a tumour

Idiopathic TN (ITN): meaning the cause is unknown.³

Who gets trigeminal neuralgia? 

TN is often underdiagnosed and misdiagnosed. Studies have found varying incidences, ranging from 4.3 to 27  per 100,000 individuals per year.^5,6 This rate is higher in individuals assigned female at birth.⁵ Age of onset can vary, but typically occurs between 43 and 53 years of age. (The condition is less common in younger patients. Secondary TN accounts for 14–20% of TN patients, and often occurs in younger individuals.^6,7 There is a strong correlation between multiple sclerosis (MS) and TN.⁸ Hypertension, or high blood pressure, may also increase the risk of developing TN, and TN may increase the risk of stroke, although this may be due to chance.⁹

What causes trigeminal neuralgia?

Classical trigeminal neuralgia may result from neurovascular compression or irritation of the trigeminal nerve by blood vessels, close to the brainstem or the "root entry zone".¹⁰ Secondary trigeminal neuralgia is caused by a lesion, such as a tumour, or multiple sclerosis (MS). Both classical and secondary neuralgia cause demyelination, damage to the protective sheath of the trigeminal nerve, causing the generation of abnormal electrical impulses in the nerve. This produces the sensation of pain.^10,11 

Diagnosis

Diagnosis of TN is based on medical history, clinical symptoms and the exclusion of other disorders. Additional testing may be necessary; An MRI scan should be performed to identify vascular structures compressing the nerve or rule out other conditions.^{12, 13}

The main diagnostic feature of trigeminal neuralgia is excruciating, shooting pain in the area of the face supplied by the ophthalmic, maxillary and mandibular nerves, which branch from the trigeminal nerve.^10,14 Pain is usually one-sided, although it may affect both sides of the face if caused by MS. There is usually minimal sensory loss.¹⁵ The ophthalmic nerve supplies sensation and movement to the forehead, scalp, eye and nose. The maxillary nerve supplies the cheek, upper jaw, upper mouth, teeth, sinuses and the palate. The pain typically results from the nerve’s maxillary and mandibular branches, whereas the ophthalmic branch is less frequently affected.^10,14 It often starts suddenly and may be severe enough to impair the ability to speak or eat, and individuals often report feeling suicidal.¹³ 

According to the International Headache Society, trigeminal neuralgia is characterised by:

1. Sudden, recurrent pain in one or more trigeminal nerve branches, lasting anywhere from a few seconds to two minutes.
2. Pain is described as being stabbing, acute, sharp, or superficial.
3. Symptoms are not explained by other neurological conditions^{2, 2}

Differential diagnosis

The main differential diagnosis is Trigeminal Autonomic Cephalalgias (TAC’s).² This group of disorders includes paroxysmal hemicrania and cluster headaches, and typically affects the ophthalmic branch, affecting the upper half of the face and eye. These conditions may be characterised by longer pain episodes lasting weeks to months, with no periods of refractory pain relief. Symptoms that differentiate TACs from trigeminal neuralgia include nasal congestion and runny nose, tears, eye redness, swelling of the upper eyelids, facial redness, and a fullness in the ear.¹⁶ Individuals with trigeminal neuralgia prefer to remain still, whereas those with TAC’s are frequently restless and disturbed. Primary headaches, such as migraine and tension-type headaches, may also present similarly, but also last longer.^2,16

Other conditions that may present similarly include: 

• Diseases of the teeth  
• Orbital cellulitis (eye infection) 
• Glaucoma (damage to the optic nerve) 
• Facial trauma, such as skeletal fractures, 
• Tumours of the facial bones or the trigeminal nerve
• Giant cell arteritis (inflammation and swelling of the arteries) 
• Tolosa-Hunt syndrome: facial pain associated with painful, restricted eye movements (idiopathic inflammation in or around the cavernous sinus)^{2, 17}

Biochemical investigations

Antiepileptic medications used to treat TN  may cause side effects such as hyponatraemia (low serum sodium concentration), increased liver transaminases, enzymes in the bloodstream that indicate damage to the liver, and decreased white blood cell counts, indicating impairment of the immune system.

The National Institute for Health and Care Excellence (NICE) suggest that individuals taking such medication should have blood tests every 2-5 years to check these levels, monitor the effects of medication and prevent toxicity.¹⁸

Treatment

Conservative treatments

• Antiepileptic medications have been the cornerstone of treatment for trigeminal neuralgia since 1860. Carbamazepine is the gold standard treatment, at 200–1200 mg/day, providing complete pain relief in 70% of individuals.^1,19 The dosage is usually increased over a few weeks. Oxcarbazepine (300–1800 mg/day) may also be prescribed, particularly in the early stages of TN.^18,20,24

When first-line medications are ineffective or if the side effects are intolerable, the following medications may be used: 

• Lamotrigine
• Gabapentin
• Botulinum toxin type A
• Pregabalin
• Baclofen
• Phenytoin²¹

These medications may be used alone or in combination with carbamazepine or oxcarbazepine. However, the evidence is weaker for these medications.²² Hospital treatment is not typically required. Up to 10% of individuals with TN do not find relief from medication.¹²

Interventional treatments

If medical treatment is ineffective or you experience too many negative side effects, surgical procedures may be performed. Up to 75% of individuals with trigeminal neuralgia undergo surgical treatments, including: 

• Surgical microvascular decompression (MVD): the vascular loop compressing the trigeminal nerve is moved away from the root entry zone as part of a craniectomy under general anaesthesia, providing lasting pain relief²²
• Stereotactic radiation therapy: damages the nerve with radiation, providing temporary relief, but may cause facial numbness²³
• Percutaneous balloon micro compression: damages the nerve by inserting a balloon catheter under general anaesthesia, crushing the nerve
• Percutaneous glycerol rhizolysis: the nerve is damaged with glycerol^11,12
• Percutaneous radiofrequency (RF): the nerve is damaged with heat²⁴ 

Conclusion

 In conclusion, trigeminal neuralgia is a rare condition characterised by brief, recurrent and severe, one-sided facial pain. It is most common in individuals assigned female at birth over the age of 40, and is usually caused by neurovascular compression of the trigeminal nerve. Diagnosis is based on clinical history and examination, and treatment options include anti-epileptic medication and surgical interventions. The condition can be debilitating and significantly impair quality and life, but can be managed effectively.