Trigeminal neuralgia

Pathophysiology

Aberrant firing of the trigeminal nerve results with either no identifiable cause (idiopathic) or due to a structural compressive lesion.

Epidemiology

Risk factors

  • Female (1.5:1)
  • Hypertension (weak)
  • Migraine (weak)

Classic presenting complaint

Episodes of brief, sharp, stabbing pain in the trigeminal nerve distribution triggered by light touch, cold air, or facial movements.

Symptoms

Patients describe episodes of intense, unilateral, electric-shock like pain in one or more sensory distribution of the trigeminal nerve (usually V2 or V3) triggered by an innocuous stimulus. Triggers include:

  • Light touch in the sensory distribution affected
  • Cold wind
  • Chewing
  • Smiling
  • Brushing teeth

Episodes last for seconds and are followed by a refractory period during which further attacks do not occur.

On examination

In between attacks of ‘classic’ trigeminal neuralgia, the examination should be normal. Any neurological deficit implies a secondary cause. Features to look out for include:

  • evidence of trigeminal neuropathy
    • wasting/weakness of muscles of mastication
    • sensory loss in the affected distribution
    • absent/impaired corneal reflex (V is afferent)
  • evidence of other cranial neuropathies
  • evidence of an underlying aetiology
    • HZV vesicles?

Clinical approach 

Once the characteristic clinical syndrome is identified the next step is to exclude secondary causes. This usually includes neuro-imaging to exclude a structural cause.

ICHD-3 criteria

  • >3 attacks which are…
  • Strictly limited to the trigeminal distribution and
  • With 3/4 of:
    • Time course of seconds
    • Severe
    • Shock-like
    • >3 episodes related to an innocuous trigger
  • With NO neurological deficit and
  • No better explanation

Differential diagnosis

Classic trigeminal neuralgia is an idiopathic trigeminal neuropathy. Several processes can also cause this picture and can be classified according to site:

Peripheral causes

  • Trigeminal neuralgia
  • Herpes Zoster
    • Acute HZV
    • Postherpetic neuralgia
  • Trauma
  • Cavernous sinus lesions (e.g. thrombosis, SOL, bleed)

CNS causes

  • Demyelination
  • Infarction
  • SOL

A structural lesion anywhere along the pathway can produce the clinical picture of trigeminal neuralgia:

Treatments

The first-line treatment for classic TN is carbamazapine. Less effective alternatives include oxcarbazepine, baclofen and lamotrigine. Drug-refractory cases can be treated with botulinum toxin injection.