Trigeminal Neuralgia 

Definition

Trigeminal neuralgia (TN) is a chronic neuropathic pain disorder characterized by recurrent, unilateral, brief, electric shock–like pains in the distribution of one or more divisions of the trigeminal nerve.

Anatomy 

Divisions:

  • V1 (Ophthalmic) → Forehead, eye (rarely involved)
  • V2 (Maxillary) → Cheek, upper lip (common)
  • V3 (Mandibular) → Jaw, lower lip (most common)

Key Site:

  • Root entry zone (REZ) at pons → most vulnerable to vascular compression

Classification (IHS / ICHD-3)

1. Classical TN

  • Due to neurovascular compression
  • Usually by:
    • superior cerebellar artery (most common)
  • Causes focal demyelination

2. Secondary TN

  • Due to structural lesion:
    • multiple sclerosis
    • Tumors (CPA tumors, meningioma)
    • AV malformations

3. Idiopathic TN

  • No identifiable cause


Pathophysiology 

  • Chronic pulsatile vascular compression → focal demyelination
  • Leads to:
    • Ephaptic transmission (cross-talk between fibers)
    • Hyperexcitability of trigeminal afferents
  • Results in:
    • Paroxysmal pain triggered by innocuous stimuli

Key concept:
Demyelination → ectopic impulse generation + ephaptic spread

 Clinical Features 

Pain Characteristics:

  • Sudden, severe, electric shock-like / stabbing pain
  • Duration: seconds to <2 minutes
  • Recurrent attacks (clusters)

Distribution:

  • Usually unilateral
  • V2 > V3 >> V1

Trigger Zones:

  • Light stimuli trigger attacks:
    • Touch, shaving, brushing teeth, talking, chewing

Refractory Period:

  • Brief period after attack where pain cannot be triggered

Between Attacks:

  • Patient is asymptomatic (classical TN)


Red Flag Features (Suggest Secondary TN)

Feature

Implication

Age < 40 years

Consider multiple sclerosis

Bilateral symptoms

Secondary cause

Sensory loss

Not classical TN

Continuous dull pain

Atypical TN

Poor response to carbamazepine

Reconsider diagnosis


Diagnosis

Clinical Diagnosis (Primary)

  • Based on ICHD-3 criteria

ICHD-3 Criteria:

  • Recurrent unilateral facial pain
  • Electric shock-like, abrupt onset/termination
  • Triggered by innocuous stimuli
  • No better alternative diagnosis


Imaging (Mandatory in all patients)

  • MRI brain with contrast + MRA
    • Detect:
      • Neurovascular compression
      • multiple sclerosis plaques
      • Tumors (CPA)


Differential Diagnosis 

Condition

Key Difference

Dental pain

Localized, persistent

TMJ disorder

Jaw movement pain

Cluster headache

Autonomic features

Postherpetic neuralgia

Continuous burning pain

Atypical facial pain

Constant, poorly localized


 Management 

 1. First-Line (Gold Standard)

Carbamazepine

  • Mechanism: Na⁺ channel blocker
  • Response is diagnostic + therapeutic

Monitoring:

  • CBC (risk of agranulocytosis)
  • LFTs

 2. Alternative First-Line

Oxcarbazepine

  • Better tolerated
  • Less drug interactions


 3. Second-Line Drugs

  • Lamotrigine
  • Baclofen
  • Gabapentin / Pregabalin

 4. Refractory TN → Surgical Management

A. Microvascular Decompression (MVD)

  • Definitive treatment
  • Relieves vascular compression
  • Best long-term results

B. Percutaneous Procedures

  • Radiofrequency ablation
  • Balloon compression
  • Glycerol rhizotomy

C. Gamma Knife Radiosurgery

  • Non-invasive option

 Complications

  • Depression, anxiety
  • Weight loss (due to fear of eating)
  • Drug side effects:
    • Carbamazepine → hyponatremia, aplastic anemia

 Special Scenario: TN in Multiple Sclerosis

  • Often bilateral
  • Younger patients
  • Poor response to carbamazepine
  • MRI → demyelinating plaques

 Exam Pearls

  • Most common nerve division: V2, V3
  • Most common vessel: superior cerebellar artery
  • Drug of choice: Carbamazepine
  • Best definitive treatment: Microvascular decompression
  • Pain type: Electric shock-like, triggered
  • Key pathology: Demyelination at root entry zone
  • Red flag: Sensory loss = NOT classical TN