Trigeminal Neuralgia

Trigeminal neuralgia (TN) is an often chronic and recurring pain syndrome involving the sensory distribution of the trigeminal nerve (cranial nerve (CN) V). The pain is typically unilateral and described as an acute, sharp, electric-shock–like pain involving the maxillary or mandibular areas and often associated with spasm of facial muscles. Trigeminal neuralgia occurs in multiple, short-acting episodes. Most cases are usually due to vascular compression of the trigeminal nerve, although secondary causes can be from aneurysms, neuromas, or other neurologic disorders. A detailed history is the hallmark for diagnosis. Neuroimaging with MRI is useful to determine the exact pathology involving the trigeminal nerve root. The 1st line of therapy is pharmacologic (carbamazepine). Other treatment options include botulinum toxin injections or surgical procedures in refractory cases.

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Editorial responsibility: Stanley Oiseth, Lindsay Jones, Evelin Maza

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Overview

Definition

Trigeminal neuralgia (TN) is a disorder presenting with recurrent, sharp pain in the distribution of the trigeminal nerve.

Anatomy of the trigeminal nerve

Trigeminal nerve (cranial nerve (CN) V):

  • The largest of all the cranial nerves
  • Starts at the mid-lateral surface of the pons
  • Sensory ganglion (Gasser ganglion) reside in the floor of the middle cranial fossa.

3 major divisions of CN V:

  • Ophthalmic (V1): 
    • Exits the cranium via the superior orbital fissure
    • Purely sensory
    • Sensory innervation of the forehead, eyes, and nose
  • Maxillary (V2):
    • Exits the cranium via the foramen rotundum
    • Purely sensory
    • Innervation of the lower eyelid, teeth, nasal cavity, gums of the upper jaw, palate, and tonsils 
    • Autonomic innervation of the lacrimal and nasal glands
  • Mandibular (V3): 
    • Exits the cranium via the foramen ovale
    • Sensory and motor
    • Motor innervation of the muscles of mastication
    • Sensory supply of the teeth, gums of the lower jaw, buccal mucosa, dorsum of the tongue, and external acoustic meatus

Epidemiology

  • Annual incidence: 4–5 per 100,000
  • Ratio of men to women: 1:1.5 
  • Onset is typically after 40 years old, but may occur at any age.

Etiology

  • Classic TN: 
    • Approximately 75% of cases result from vascular (artery or vein) compression of the trigeminal nerve at the entry zone of the root. 
    • The compression is commonly caused by a branch of the superior cerebellar artery.
  • Secondary TN: 
    • 15% of cases are caused by an underlying disease.
    • Common causes include:
      • Multiple sclerosis
      • Vestibular schwannoma (acoustic neuroma)
      • Meningioma
      • An epidermoid cyst or other cyst
      • Arteriovenous malformation
      • Aneurysms
  • 10% are classified as idiopathic TN (unidentified cause).

Clinical Presentation

Main reported symptoms

  • Sudden, stabbing, unilateral facial pain:
    • Frequent unilateral pain
    • In rare cases (3% of individuals with TN), pain can be active on both sides at the same time. 
    • The pain is a severe, sharp, shooting, or electric-shock–like sensation, lasting seconds to 2 minutes. 
    • Facial grimacing or spasm may accompany the pain (tic douloureux).
  • Individuals report “trigger zones” (usually midline around the nose and lips):
    • Even nonpainful stimuli in the trigger zones can cause pain. 
    • Stimuli include:
      • Chewing
      • Washing the face
      • Talking
      • Brushing the teeth
      • Shaving
      • Cold air
    • After the initial pain, a refractory period may last up to several minutes.
    • Stimulation of the trigger zone will not cause pain during the refractory period.
  • Autonomic symptoms (V1 involvement):
    • Lacrimation
    • Rhinorrhea
    • Conjunctival injection
  • TN attacks:
    • May occur for extended periods of time (weeks to months)
    • In many cases, remission can last at least 6 months.
    • Recurrence is common (frequency and severity wax and wane).
    • During periods with multiple attacks, affected individuals report depressed mood (↑ suicide risk) and disturbances in eating and sleeping.

Associated symptoms

When other neurologic conditions (e.g., multiple sclerosis or aneurysms) are present, additional symptoms may include:

  • Visual/ocular manifestations
  • Weakness
  • Neuropathy
  • Seizures
  • Hearing loss
  • Tinnitus
  • Cutaneous tumors

Diagnosis

Diagnosis of TN is clinical with a thorough history and physical. Further workup with imaging or laboratory studies may be required if red-flag symptoms are present.

History

  • Diagnostic criteria based on the International Classification of Headache Disorders 3rd Edition:
    • Paroxysms or attacks of unilateral facial pain are recurrent in areas supplied by 1 or more divisions of the trigeminal nerve.
    • Pain characteristics:
      • Duration: a few seconds to ≤ 2 minutes 
      • Severe intensity
      • Shooting, stabbing, sharp, or electric-shock–like pain 
      • Innocuous stimuli within the affected trigeminal distribution triggers the pain.
      • No other alternative diagnosis
  • Red-flag symptoms: 
    • Age of onset < 40 years old
    • Changes in sensation
    • Deafness
    • History of skin lesions
    • Poor response to medications (carbamazepine)

Physical examination

  • Neurologic examination findings are normal:
    • Facial sensation is intact.
    • Bulk and strength of the masseter muscles are normal.
    • Corneal reflexes are normal.
  • Any permanent area of numbness excludes the diagnosis.
  • If sensory loss is found, exclude multiple sclerosis (MS) or a structural lesion.

Ancillary studies

  • MRI:
    • Recommended to rule out nerve compression or structural brain lesion
    • High-resolution MRI with thin cuts through the region of the trigeminal ganglion + heavy T2 weighting with or without contrast 
    • Confirms morphological changes such as dislocation, distortion, atrophy, or compression of the trigeminal nerve at the origin from the pons
  • CT:
    • An alternative only when MRI is unavailable
    • Not as sensitive as MRI of the brain
  • Laboratory workup:
    • Used at baseline to monitor adverse effects from medications 
    • Includes CBC, serum electrolytes, and liver function panel

Management

  • Classic and idiopathic TN:
    • 1st line-therapy: carbamazepine or oxcarbazepine:
      • Mechanism of action is inhibition of neuronal sodium channel activity to reduce the excitability of neurons.
      • 58%–100% of individuals achieve complete or partial pain control (lack of response is a red-flag finding)
      • Common side effects: vertigo, sedation, ataxia, and nausea
    • Alternative agents (can be used individually or combined):
      • Baclofen
      • Lamotrigine
      • Gabapentin
    • Botulinum toxin injections: Consider in the elderly or if oral medications and more invasive management cannot be tolerated.
    • Surgical procedures: for individuals refractory to medical management:
      • Microvascular decompression (commonly used if unable to tolerate a major procedure)
      • Rhizotomy
      • Gamma knife radiosurgery
      • Balloon compression 
  • For secondary TN, management of the underlying etiology is critical.
  • Screen and treat comorbid psychiatric conditions (e.g., depression and anxiety).

Differential Diagnosis

  • Postherpetic neuralgia: viral reactivation of the varicella zoster virus (VZV). Age, stress, or immunocompromised states can trigger the reactivation of the virus. Postherpetic neuralgia presents as a painful, unilateral rash distributed in a single dermatomal distribution (often in the thoracic region or along the trigeminal distribution). Diagnosis is clinical. Management includes antiviral therapy and symptomatic treatment. 
  • Migraine: a prevalent primary headache disorder characterized by episodic, moderate-to-severe headaches, which may be associated with nausea and/or vomiting and increased sensitivity to light and sound. Migraine headache is a clinical diagnosis with several variants. Management strategies include abortive therapy including NSAIDs and triptans to manage acute episodes, as well as preventative strategies to minimize morbidity and pain-related disability.
  • Cluster headaches: a primary headache disorder characterized by moderate-to-severe unilateral headaches occurring in conjunction with autonomic symptoms. Cluster headaches are characterized by attacks ≤ several times per day for weeks to months, followed by a pain-free remission period. The diagnosis is clinical and often easy to establish due to the distinct features. The 1st line of treatment involves administration of oxygen by nasal cannula and/or abortive therapy with a triptan. Preventative strategies (e.g., glucocorticoids or verapamil) are crucial.
  • Short-lasting unilateral neuralgiform headache attacks with conjunctival injection and tearing (SUNCT): a rare form of headache characterized by bursts of severe burning/throbbing with unilateral pain lasting a few seconds to minutes, affecting the head and around the eye or temple. Short-lasting unilateral neuralgiform headache attacks with conjunctival injection and tearing are also associated with autonomic nervous system responses such as tearing, conjunctival injection, nasal congestion, and sweating. The attacks may be relieved with corticosteroids and antiepileptic drugs, but are generally nonresponsive to the usual analgesics. Trigeminal neuralgia has a refractory period after the pain, but SUNCT does not. Neuroimaging also shows neurovascular contact in many cases of TN.

References

  1. Bennetto, L., Patel, N. K., & Fuller, G. (2007). Trigeminal neuralgia and its management. Bmj, 334(7586), 201–205

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