Trigeminal neuralgia (TN), also called tic douloureux or Fothergill disease, is a paroxysmal, sharp, unilateral, stabbing and extreme facial pain syndrome in one or more divisions of the trigeminal nerve. This pain lasts seconds up to 2 minutes, but can sometimes be constant.
This is a rare condition that is not commonly seen in those below 60 years of age. It also affects women more than men.
🦴 Anatomy
The trigeminal nerve (CN V) is the largest cranial nerve which is a mixed nerve with both sensory and motor functions.
The sensory root of the trigeminal nerve is found on the brainstem at the level of the pons.
The trigeminal nerve has 3 divisions:
- V1 - the ophthalmic nerve. It innervates the forehead, scalp, frontal and ethmoidal sinuses, upper eyelid and upper conjunctiva, cornea and dorsum of the nose. As it supplies the cornea it is also responsible for the corneal reflex. It exits the skull via the superior orbital fissure. It then travels through the lateral wall of the cavernous sinus before reaching the trigeminal ganglion.
- V2 - the maxillary nerve. It innervates the lower eyelid and the lower conjunctiva, the cheeks and maxillary sinuses, nasal cavity, lateral nose, upper lip and upper teeth and superior palate. It exits the skull via the foramen rotundum. It also travels through the lateral wall of the cavernous sinus before reaching the trigeminal ganglion.
- V3 - the mandibular nerve. It innervates the mucous membranes, floor of the oral cavity, external ear, lower lip, chin, anterior 2/3rds of the tongue (for sensations other than taste), and the lower teeth. It exits the skull via the foramen ovale. The motor root also passes with the mandibular division to supply the muscles of mastication.
Pathophysiology
Most patients with TN have a vascular loop that is compressing the trigeminal nerve. This is usually the superior cerebellar artery (SCA) in 75% of cases. In other cases, it is the anterior inferior cerebellar artery (AICA) may be imlplicated. 12% of the time, a vein is causing the compression, and sometimes both an artery and vein are involved.
This vascular loop causes demyelination of the root which results in abnormal nerve impulses being fired. In TN ephaptic transmission may occur. This is when adjacent nerve fibres cause firing of the nerve without direct synaptic connections or neurotransmitters activating the nerve.
Other causes of TN may be tumours as well as multiple sclerosis (MS). Patients with MS are 20x more likely to have TN. This is due to demyelinating plaques found at the pons where we find the trigeminal root.
Even more rarely we have seen TN being associated with amyloid deposits (trigeminal amyloidoma), calcium deposits and even pontine infarctions.
🔢 Classification
- Classical TN - this occurs in 3/4th of the caes. TN is due vascular compression of the trigeminal nerve root, most commonly the SCA.
- Secondary TN - occurs in 15% of cases. TN is caused by another pathological process such as multiple sclerosis, arteriovenous malformation, cerebellopontine angle tumour.
- Idiopathic TN - this makes up 10% of cases. diagnosed when no lesion or disease that could cause trigeminal neuralgia is found.
⚠️ Risk factors
- Advancing age
- Multiple sclerosis
- Hypertension
😷 Presentation
- Unilateral facial pain - the pain is paroxysmal, severe shooting or stabbing (like an electric shock), followed by a burning ache. It typically occurs from the mouth → angle of jaw.
- Occurs at rest or after triggers:
- Triggers include chewing, talking, touch, shaving, brushing teeth, washing face, breeze of air.
- Lasts several seconds - up to minutes.
- May occur up to 100 times a day.
- Facial spasms may occur
- Psychological distress - ranging from dysphoria to severe depression with suicidal tendencies.
🔍 Investigations
⭐️ The diagnosis is a clinical diagnosis.
- MRI - should be performed at least once in the patient's lifetime to evaluate for structural etiology.
- Neurologic examination - normal in trigeminal neuralgia. Thus, neurologic deficits (usually loss of facial sensation) suggest that the trigeminal neuralgia–like pain is caused by another disorder.
The International Classification of Headache Disorders has criteria for diagnosing TN that may help:
- Recurrent, paroxysmal unilateral facial pain in ≥1 of the distributions of the divisions of the trigeminal nerve (and not radiating beyond). The pain lasts from fractions of a second to up to 2 minutes. It is severe and like an electric shock or shooting, stabbing or sharp in quality.
- Precipitated by innocuous stimuli (in the affected area)
- Not better accounted for by an alternative diagnosis
🧰 Management
NICE recommends the following:
- 🥇 Carbamazepine - this is recommended as the initial treatment.
- 🥈 Refer to specialist pain service
The BMJ has additional advice which may be helpful:
- Gabapentin or pregabalin - may be used as monotherapy or may be additional therapies on top of carbamazepine if monotherapy with carbemazepine is not useful. They are less effective but have less adverse effects.
- If unresponsive to medications, we can consider a couple of options:
- Classical TN → microvascular decompression.
- Secondary TN → treat underlying cause/condition.
- Idiopathic TN → ablative surgery.