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Sunday, August 10, 2025

Trigeminal neuralgia


Definition
Trigeminal neuralgia is a chronic pain condition characterised by sudden, severe, brief, recurrent episodes of unilateral facial pain in the distribution of one or more branches of the trigeminal nerve (cranial nerve V). It is sometimes referred to as "tic douloureux" due to the involuntary facial twitching that can accompany attacks.

Causes

  • Primary (classic) TN: Usually due to vascular compression of the trigeminal nerve root by an aberrant loop of a superior cerebellar artery or vein → demyelination of nerve fibres

  • Secondary TN: Due to structural lesions (tumours, cysts, arteriovenous malformations, multiple sclerosis plaques)

  • Idiopathic: No identifiable cause on imaging

Risk Factors

  • Age >50 years (peak incidence 60–70 years)

  • Female sex (slightly more common)

  • Multiple sclerosis

  • Family history (rare, in some genetic syndromes)

Pathophysiology
Compression/damage to the trigeminal nerve root causes abnormal ephaptic transmission between nerve fibres, leading to paroxysms of pain in response to minimal stimulation (e.g., light touch).

Clinical Features

Pain Characteristics:

  • Severe, stabbing, electric-shock-like pain

  • Lasts seconds to 2 minutes per episode

  • Unilateral, following distribution of CN V branches (V2 – maxillary, V3 – mandibular most common; V1 – ophthalmic less common)

  • Triggered by light touch, chewing, speaking, washing face, cold wind

Neurological Examination:

  • Usually normal in primary TN

  • Sensory loss suggests secondary cause and warrants urgent imaging

Diagnosis

  • Clinical diagnosis based on history and normal neurological exam (in primary TN)

  • MRI with trigeminal nerve protocol to exclude secondary causes and detect neurovascular compression

Treatment

1. First-line pharmacological therapy

  • Carbamazepine

    • Initial dose: 100 mg twice daily, titrated gradually

    • Typical maintenance: 200–400 mg twice daily (max 1200 mg/day)

    • Monitor CBC and liver function due to risk of bone marrow suppression and hepatotoxicity

  • Oxcarbazepine

    • Alternative first-line; better tolerated in some patients

2. Second-line / adjunct medications

  • Lamotrigine

  • Baclofen (can be combined with carbamazepine)

  • Gabapentin or pregabalin (less robust evidence)

3. Surgical / interventional options (for refractory cases)

  • Microvascular decompression (MVD) – most durable long-term relief for classic TN with vascular compression

  • Percutaneous procedures (glycerol rhizotomy, radiofrequency thermal lesion, balloon compression)

  • Stereotactic radiosurgery (Gamma Knife)

4. Supportive measures

  • Patient education on trigger avoidance

  • Psychological support for chronic pain impact

Prognosis

  • Many respond well to carbamazepine or oxcarbazepine

  • Condition often follows a relapsing–remitting course; may progress in frequency/severity

  • Surgery can provide long-term relief in selected cases




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