Trigeminal Neuralgia and other Facial Pain

Essentials

• Trigeminal neuralgia is characterized by paroxysms of intense pain resembling electrical shock-like pain on one side of the face in the distribution of one or two of the branches of the trigeminal nerve.
• Trigeminal neuralgia is divided into three types: classical (the most common), secondary (15% of cases) and idiopathic (10% of cases).
• The first line drugs are carbamazepine and oxcarbazepine.
• Gabapentin, pregabalin, venlafaxine, duloxetine, amitriptyline or nortriptyline, for example, can be used as additional or alternative drugs.
• In drug-resistant cases, repetitive transcranial magnetic stimulation (rTMS) or a neurosurgical procedure can be considered.
• Brain MRI is recommended to exclude secondary causes.
• In addition to other treatments, support by a psychologist or a nurse is recommended.

Symptoms

• The pain is situated on the face in the distribution of one or more trigeminal nerve branches, and is usually unilateral (picture 1).
• The pain comes in short attacks of shooting, electric shock-like pain (lasting from one second to about 2 minutes, usually a few seconds), and it may be very severe.
• The pain may typically be triggered by a painless external factor: touching the face, speaking, eating, brushing the teeth.
• About 25-50% of patients have concomitant continuous facial pain in the same area as the short attacks of shooting pain. The pain may be burning or pulsating, for example.
• There are intermittent remission phases, during which analgesic medication can be reduced and/or paused.

Pathophysiology

• Where the trigeminal nerve joins the brainstem, the Schwann cells in the myelin sheath are replaced by oligodendrocytes of the central nervous system.
• At this point, the nerve is sensitive to damage and to demyelination.
  • Due to vascular compression in classical trigeminal neuralgia
  • Due to a plaque of demyelination from multiple sclerosis in secondary trigeminal neuralgia
• Local myelin damage leads to abnormal depolarization (hyperexcitability) and possibly to sensitization of the pain pathway.

Diagnostic criteria

1. Recurrent episodes of unilateral facial pain restricted to the distribution of one or two trigeminal nerve branches, with no pain radiating elsewhere
2. Typical features of the pain:
   • duration from a few seconds to 2 minutes
   • intense
   • electric shock-like, shooting, stabbing or sharp.
3. Episodes of pain are (usually) preceded by a triggering factor in the painful trigeminal nerve area, such as speaking or light touching of the face (trigger point).
4. Not attributable to any other disorder in the International Classification of Headache Disorders (ICHD-3).

Classification

• Classical trigeminal neuralgia (the most common form): vascular compression of the trigeminal nerve root is detected by brain MRI, with associated morphological changes (such as atrophy or dislocation).
• Secondary trigeminal neuralgia (about 15% of cases): another cause is detected by brain MRI, such as an MS plaque or a tumour in the pontine angle damaging the trigeminal nerve root and causing trigeminal neuralgia.
• Idiopathic trigeminal neuralgia (about 10% of cases): no cause can be found in investigations.

Causes and diagnosis

• In idiopathic trigeminal neuralgia there is no underlying disease or neurovascular compression of the trigeminal nerve root causing the condition. About 10% of the patients belong to this group. In the majority of patients the symptoms are explained by neurovascular compression of the trigeminal nerve root in the brain stem.
• Secondary trigeminal neuralgia has similar symptoms to the idiopathic form but it is caused by another disease, e.g. MS or a brainstem tumour.

Treatment Psychosocial Interventions for Chronic Orofacial Pain, Antipsychotics for Acute and Chronic Pain, Opioids for Chronic Non-Cancer Pain

• Either fosphenytoin (dosage by weight, monitoring) or lidocaine infusion is recommended for acute exacerbations. There is little data available on the treatment of acute exacerbations.
  • Potent opioids are not recommended.
• The drug of choice is carbamazepine Carbamazepine for Acute and Chronic Pain. Find out about local reimbursement policy (a neurologist's certificate may be required for highest reimbursement level).
• Oxcarbazepine is an alternative and may be tried especially if carbamazepine causes adverse effects (fatigue, dizziness) or when there is a need to avoid the interactions of carbamazepine with other drugs. A derivative of carbamazepine, oxcarbazepine is better tolerated and as effective as carbamazepine. The reimbursement policy may differ from that of carbamazepine.
• The initial dose of carbamazepine is 100 mg twice daily and can be increased to 1 200 mg/24h, as necessary.
• The initial dose of oxcarbazepine is 150 mg twice daily and can be increased to 1 800 mg/24h, as necessary.
• In the beginning, follow-up of blood cell counts and liver function tests is recommended. Carbamazepine concentrations can be measured if there are signs of overdose (dizziness, tiredness, diplopia or nystagmus).
• If the first-line drugs are ineffective, the following, for example, can be used as add-on or alternative drugs:
  • Lamotrigine as an add-on drug to carbamazepine Lamotrigine for Acute and Chronic Pain (note: risk of skin rash when increasing the dose); it can also be used as monotherapy.
  • Gabapentin, pregabalin or valproic acid may be tried as secondary alternatives.
    • Based on clinical experience, gabapentin appears to be less effective than carbamazepine or oxcarbazepine. Nevertheless, it can be added to these or used as monotherapy in patients who cannot use the first-line drugs due to their adverse effects.
  • Baclofen can be used as an add-on drug or as monotherapy.
    • The dose may be increased up to 80 mg/24h, as necessary.
• If trigeminal neuralgia is refractory to drug treatment or symptomatic neurovascular compression can be seen in brain MRI, the patient can be referred for assessment to a department of neurosurgery.
• The most commonly used neurosurgical treatment modalities include microvascular decompression, i.e. microsurgical release of trigeminal nerve root compression caused by a tortuous artery, and coagulation of the trigeminal ganglion Surgical Modalities for Trigeminal Neuralgia.
• In cases refractory to treatment, neuromodulation, such as repetitive transcranial magnetic stimulation (rTMS), can also be used.

Other neuropathic pain in the facial area

• In other types of neuropathic facial pain, damage to a branch of the trigeminal nerve has led to a neuropathic pain state. The pain is usually a constant steady, dull, aching or burning pain, and the patient may additionally experience electric shock-like pain. Usually, the pain does not disturb sleep at night.
• The most common causes of neuropathic facial pain include facial injuries, sequelae of surgical interventions (such as sinus puncture, root canal treatment, tooth extraction, plastic surgery) and postherpetic neuralgia.
• The pain may also emerge after a cerebrovascular disorder (central post stroke pain). In these patients, the pain and the sensory disturbance are not necessarily limited to the facial area.
• In patients with neuropathic facial pain, careful sensory testing of the trigeminal nerve or neurophysiological investigations (blink reflex test or quantitative sensory threshold measurement) will give abnormal findings.
• If a patient is diagnosed with neuropathic facial pain of unclear origin, he/she should be referred to an outpatient neurology clinic for further investigations.

Other facial pain

• Facial or oral pain occurs in 17-26% of the population; 10% of these cases are chronic.
• Acute facial pain is most commonly caused by sinusitis (0.7%) or by factors of dental origin (1.2%). The aetiology may also be temporomandibular dysfunction (TMD; 5%), or the pain may be referred from the anterior neck (e.g. thyroiditis) or from the back of the neck (e.g. tension neck).
• So-called atypical facial pain (0.9%) is a much more common type of prolonged facial pain than trigeminal neuralgia (0.01%).
  • The pain is usually constant and dull. It may cross the midline and is also otherwise independent of dermatomal boundaries. Sensory testing gives abnormal findings.
  • The pain is often triggered by trauma, interventions involving the face/sinuses/mouth (not, however, being a complication of the intervention), infection or stress.
  • Persistent idiopathic facial pain (PIFP, burning mouth, atypical facial pain, atypical toothache) is currently considered to be nociplastic, i.e. arising from altered nociception, and most commonly occurs in middle-aged women. The patients are often subjected to psychosocial stress.
• Clinical examination of a patient with facial pain includes teeth, masticatory muscles, temporomandibular joints, cervical spine and muscles of the neck and shoulders. It may also be advisable to examine the ears, nose and throat as well as the eyes and the anterior neck.
• If neuropathic pain (such as glossopharyngeal neuralgia) is suspected, a neurological examination is important, especially examination of the cranial nerves.
• A patient with severe or progressive facial pain should be referred for further investigations either to the department of neurology or ENT or to a special pain clinic, according to the local practice guidelines.
• See also cluster headache (Horton's neuralgia): Cluster Headache (Horton's Syndrome).

Treatment