FRCA Notes

Trigeminal Neuralgia

Trigeminal neuralgia appeared as a CRQ in 2021 (68% pass rate), with only exam technique, rather than knowledge, criticised by the examiners.

Resources

  • Also known as tic douloureux, trigeminal neuralgia is a neuropathic cranio-facial pain syndrome
  • Follows a relapsing-remitting course, with remissions as long as years
  • Annual incidence 26/100,000 in the UK
  • More common in females (3x)
  • Peak incidence 60 - 70yrs

  • A specific identifiable cause (tumour, AVM, MS) is only found in 5-10% of cases

Classical trigeminal neuralgia

  • Accounts for >80% of cases
  • Occurs due to compression of the trigeminal ganglion due to aberrant arterial, or less commonly venous, loops
  • The most common vasculature involved are the superior cerebellar artery, anterior inferior cerebellar artery, and the basilar artery

  • With age, the intracranial vessels become elongated and redundantly looped
    • This increases neurovascular contact with the trigeminal roots/ganglion
    • Pulsatile vascular indentation of the roots leads to focal demyelination
    • Demyelinated areas may generate ectopic impulses or respond differently to normally innocuous afferent impulses

Secondary trigeminal neuralgia

  • Multiple sclerosis (5%)
  • Arteriovenous malformations
  • Chiari malformations
  • Neoplasms e.g. acoustic neuromas, meningiomas, pontine lesions

  • Characterised by paroxysms of intense, severe, lancinating facial pain
  • Typically lasts seconds-to-minutes
    • Starts and ends abruptly
    • Daily frequency ranges from 1-2 up to several hundred
  • 'Electric shock' or 'stabbing' pain
  • Almost always unilateral
  • Affects the maxillary and mandibular branches more commonly
  • There is no motor weakness in the vast majority of patients

Triggers

  • 90% of patients will have triggers for their pain, which are usually benign:
    • Washing the face
    • Chewing food
    • Brushing teeth
    • Smiling
    • Exposure to wind
    • Vibtrations

  • Essentially a clinical diagnosis, based on:
    • Stereotypical pattern of attacks
    • Pain is superficial, sharp/stabbing/intense and precipitated by trigger factors
    • Attacks are stereotyped within the individual patient
    • No other neurology present
    • Symptoms not attributed to other disorder

  • MRI is indicated to exclude other causes of pain
    • Sensitive for diagnosis of MS
    • Enables visualisation of posterior fossa, where causative neoplasms may be found

Differential diagnosis

  • Post-herpetic neuralgia
  • Temporal arteritis
  • TMJ dysfunction
  • Migraine
  • Cluster headaches
  • Tumours e.g. acoustic neuroma, meningioma
  • Dental pain e.g. abscess

Conservative

  • MDT approach including psychological support

Pharmacological

  • Carbamazepine is the drug of choice, with an NNT of 1.8
    • Commence treatment at a low dose and increase the dose every 3-7 days until suitable effect achieved
      • E.g. 100mg BD initially, increased up to 200mg QDS
    • The major limiting factor is side-effects

  • Alternative pharmacotherapy includes:
    • Oxcarbazepine (similar efficacy and better side effect profile)
    • Gabapentinoids are not as effective but may be a second line option
    • Amitriptyline is not as effective
    • Can add on lamotrigine or baclofen
    • Phenytoin

Surgical

  • Surgery is indicated in refractory cases
Surgical option Advantages Disadvantages
Neurolysis of branches of the trigeminal nerve (rhizotomy)
E.g. using alcohol injection or LASER		 Less invasive Short-term relief (6-12months)
Risk of dysaesthesia
Ablation of the trigeminal (Gasserian) ganglion
E.g. thermal (perc. RF ablation), chemical (glycerol), mechanical		 Longer-term relief (4-5yrs)
Effective in 90%		 High incidence dysaesthesia/anaesthesia
Recurrence (10-25%)
Aseptic meningitis
Cardiac arrhythmia
Microvascular decompression in the posterior fossa High success rate (80-90%)
Low recurrence rate		 Invasive, requiring craniotomy
Aseptic meningitis
Hearing loss
CSF leak
Cardiac arrhythmia