What is trigeminal neuralgia?

Trigeminal Neuralgia: Definition, Diagnosis, and Management

Trigeminal neuralgia is a chronic neuropathic pain condition characterized by brief, electric shock-like, severe, stabbing, recurrent episodes of pain within the distribution of one or more branches of the trigeminal nerve, typically triggered by innocuous stimuli such as light touch, eating, or talking. 1, 2

Clinical Characteristics

• Pain characteristics:

  • Sudden, unilateral, severe, brief (seconds to minutes)
  • Electric shock-like, stabbing, lancinating quality
  • Affects one or more branches of the trigeminal nerve (ophthalmic V1, maxillary V2, mandibular V3)
  • Pain-free intervals between attacks

• Triggers:

  • Non-noxious stimuli including:
    • Light touch to face
    • Washing face
    • Cold wind
    • Eating or chewing
    • Brushing teeth
    • Talking
    • Shaving

• Important features:

  • Typically no sensory deficits on examination (distinguishing feature)
  • Some patients may develop persistent background pain
  • Facial spasms may occur during intense flare-ups 2
  • Trigger zones are small areas where minimal stimulation precipitates pain 2

Classification

1. Classical Trigeminal Neuralgia:

   • Caused by neurovascular compression at the trigeminal root entry zone
   • Most common form

2. Secondary Trigeminal Neuralgia:

   • Caused by identifiable conditions such as:
     • Multiple sclerosis
     • Tumors
     • Other structural lesions

3. Idiopathic Trigeminal Neuralgia:

   • No identifiable cause 2

Pathophysiology

The predominant mechanism is demyelination of primary sensory trigeminal afferents in the root entry zone, leading to:

• Generation of ectopic impulses
• Ephaptic crosstalk between nerve fibers
• In many cases, caused by vascular compression of the trigeminal nerve root 3

Diagnosis

Diagnosis is primarily clinical, based on history and examination:

• Imaging: Contrast-enhanced MRI is essential to:

  • Rule out secondary causes (tumors, multiple sclerosis)
  • Identify neurovascular compression
  • MR angiography can evaluate vascular compression 1

• Examination:

  • Typically normal between episodes
  • May demonstrate light touch-evoked pain
  • Rarely shows sensory changes (if present, suggests alternative diagnosis) 1

Management

Pharmacological Treatment

1. First-line therapy:

   • Carbamazepine: 400-1200 mg daily in 2-3 divided doses

     • 70% of patients show partial or complete pain relief
     • Number needed to treat (NNT) of 1.7
     • Regular monitoring of blood counts, liver function, and sodium levels required
     • ECG screening recommended for patients over 40 1

   • Oxcarbazepine: Alternative with similar efficacy but fewer side effects (30.3% vs 43.6%) 1

2. Second-line/adjunctive therapy:

   • Lamotrigine (particularly useful with carbamazepine, NNT 2.1)
   • Baclofen (NNT 1.4)
   • Pregabalin 1

Surgical Interventions

Consider when medical therapy fails or side effects are intolerable:

1. Microvascular decompression (MVD):

   • Optimal for patients with typical TN and identifiable neurovascular compression
   • 70% remain pain-free at 10 years
   • Preserves trigeminal nerve function (no sensory loss)
   • Risks: 0.2-0.4% mortality, 1-4% hearing loss 1

2. Stereotactic radiosurgery (Gamma Knife):

   • 75% initial complete pain relief
   • 50% maintain relief at 3 years
   • Pain relief typically occurs within three months
   • Most common complication is sensory disturbance 1

3. Ablative procedures:

   • Radiofrequency treatment of Gasserian ganglion (recommended for elderly patients)
   • 50% chance of being pain-free for 4 years
   • Results in sensory loss 4

Treatment Algorithm

1. Initial approach: Start with carbamazepine or oxcarbazepine
2. If inadequate response: Add adjunctive therapy (lamotrigine, baclofen, or pregabalin)
3. If medical therapy fails or intolerable side effects:
   • For younger patients: Consider microvascular decompression
   • For elderly patients: Consider radiofrequency treatment of Gasserian ganglion

Important Considerations

• Monitoring: Regular blood counts, liver function, and sodium levels with carbamazepine
• Drug interactions: Carbamazepine induces hepatic enzymes affecting other medications
• Dose adjustments: Small adjustments in carbamazepine plasma concentration should be made carefully
• Quality of life: TN has significant impact on quality of life and socioeconomic functioning 4
• Early neurosurgical consultation: Should be sought if medication efficacy decreases 5

Trigeminal neuralgia is an excruciating condition that requires prompt diagnosis and treatment to improve quality of life. With appropriate management, most patients can achieve significant pain relief.