Trigeminal Neuralgia

Synonyms: Tic Douloureux

Trigeminal neuralgia (TN) can be described as a chronic, debilitating condition resulting in intense and extreme episodes of pain in the face. The episodes are sporadic and sudden and often like "electric shocks" lasting from a few seconds to several minutes.

Trigeminal neuralgia results from a neuropathic disorder of the fifth cranial nerve (trigeminal nerve). The trigeminal nerve senses mixed modalities including:

• Sensation
• Nociception
• Thermoception
• Motor supply to the muscles of mastication

Most commonly the maxillary and/or mandibular branch are involved.¹

• Most commonly episodes occur after the age of 40.
• Annual incidence of about 4-5 per 100,000² (however, these are based on strict case definitions and the true value may be almost six times higher).³
• More common in females.
• There may also be a genetic predisposition as there have been observations of familial clustering. However, the exact method of transmission is unclear although there is a lack of penetrance.⁴
• 2-4% of patients will actually have multiple sclerosis.

• Compression: blood vessels may press on the trigeminal nerve as it leaves the brain stem at its cerebellopontine nerve root. Compression of the nerve leads to demyelination. This results in spontaneous generation of electric impulses. This probably accounts for up to 90% of cases that were originally classified as idiopathic.³
• Degeneration: some have postulated it to be part of the ageing process as with increasing age the brain atrophies leading to redundant arterial loops which can cause compression.²
• Myelin sheath infiltration e.g. tumour or amyloidosis.
• Idiopathic

• There may be preceding symptoms e.g. tingling or numbness
• Patients may have certain triggers that set the pain paroxysm off (see table below)
• Followed by sharp, severe, shock like pains
• These pains are usually on one side in the cheek or face but pain can involve the eyes, lips, nose and scalp
• Episodes are intermittent but can last days, weeks or months on end and then not return for months or even years
• 3-5% of patients will have bilateral pains¹

Triggers of trigeminal neuralgia

• Vibration
• Skin contact e.g. shaving, washing
• Brushing teeth
• Oral intake
• Exposure to wind

Atypical trigeminal neuralgia

This subgroup of patients have relentless underlying pain like a migraine associated with superimposed stabbing pains. There may also be an intense burning sensation. This condition is particularly difficult to treat.

• Dental pathology
• Temporomandibular joint dysfunction
• Migraine
• Temporal arteritis (TN rarely affects forehead alone)
• Cluster headaches
• Multiple sclerosis and other disorders of myelin
• Overlying aneurysm of a blood vessel
• Tumour in posterior fossa e.g. meningiomas
• Arachnoid cyst at the cerebellopontine angle⁵
• Postherpetic neuralgia after shingles

The diagnosis is clinical and it can be difficult to make. No investigations are required initially unless there is uncertainty regarding the diagnosis. Patients who are referred on for specialist review will usually have a brain MRI - this is to document the presence of compression and look for other intracranial causes of TN (5-10% of patients e.g. aneurysm, MS).⁵ There should be a lower threshold for earlier investigations in the following groups: younger patients, atypical symptoms, focal neurology and poor response to initial therapy.³

Unfortunately there is no cure at present although newer surgical procedures are proving promising.

Management involves three aspects

1. Support and education
2. Medical
3. Surgical

Support and education

• Patients need to be made aware that the condition is not life-threatening
• Need however also to express empathy towards severity of the condition
• Education as to the causes and potential therapies
• Reassurance and support groups

Medical

• Typical analgesics and opioid analgesics - these are unfortunately not very successful and they are thus not first line.
• Anticonvulsants e.g. carbamazepine or gabapentin. Carbamazepine and gabapentin are first line. Carbamazepine should be tried initially and the dose uptitrated to achieve pain control. If it fails to relieve the pain or adverse effects develop then try gabapentin. However, there is a need for further randomised clinical trials to establish the effectiveness of these medications. These effects may be enhanced with baclofen and clonazepam - however, the efficacy is not well established and to date studies only involve a small number of patients.^1,6
• Once patients have been in remission for 1 month the drug should be gradually withdrawn.¹
• Tricyclic antidepressants e.g. low dose amitriptyline - the data supporting their use at present is lacking and CKS does not support their use.¹
• Other drugs that might be used in a specialist setting include lamotrigine and baclofen.

When and who to refer¹

Surgery

Most of the improvements in the management of trigeminal neuralgia have occurred because of advances in surgical treatments. Surgery involves either relieving pressure on the trigeminal nerve or damaging it to prevent any pain transmission.

There are various types of surgical procedures that can be used in trigeminal neuralgia:

• Rhizotomy - the aim is to damage the trigeminal nerve. This is an alternative to the more invasive decompression. These methods include:
  • Percutaneous glycerol rhizotomy (under a local anaesthetic)
  • Percutaneous balloon compression rhizotomy (under a general anaesthetic)⁷
  • Radio-frequency rhizotomy (performed under sedation)
  These procedures are good in the frail elderly patient or those with co-morbidities but unfortunately the affects are short lived and symptoms usually recur. They are usually associated with some level of sensory loss and can be repeated if necessary.
  
  
• Stereotactic radiosurgery (gamma knife): - this is also a form of rhizotomy that uses radiation targeted at the trigeminal nerve root and thus injures it. Pain relief is usually delayed for a few days and there can be associated facial numbness. At present the number of locations providing this treatment is limited.³
  

  NICE guidance on the use of stereotactic surgery in trigeminal neuralgia:8 Surgery to be considered if severe pain or side effects from medication A systematic review commissioned by NICE reported that between 33% - 90% achieved immediate pain relief with this procedure - only an average of 14% had recurrence of symptoms at 18 months

  
  
  
• Microvascular decompression:
  • The idea here is that blood vessels are compressing the trigeminal nerve. Thus lifting these blood vessels away reduces the pressure. This requires a general anaesthetic. The approach is behind the ear into the posterior fossa on the affected side. Patients are usually assessed by MRI beforehand to look for the presence of compression.
  • This procedure however is not with out risks. There is a risk of a cerebrovascular event, deafness and even death.^9,10 The rates of these are dependant upon the surgeons expertise. However, it is associated with the best chance of long-term pain relief. The pain relief may not occur for a few weeks and there is little sensory loss.³

Success rates with all surgical procedures are generally good with almost 3/4 of patients being positively effected. Percutaneous microballoon compression is safe for elderly patients.⁷ However, nearly all procedures cause some numbness and in a few this can be associated with intense pain obviating the whole point of the surgery ("anaesthesia dolorosa"). Microvascular decompression, although more risky, is increasingly used as it provides the longest period of pain relief and there is no sensory loss.

Due to the lack of curative measures the use of complementary therapies in trigeminal neuralgia has evolved quite rapidly. These include the following:

• TENS
• Acupuncture
• Biofeedback
• Vitamin therapies e.g. vitamin B
• Nutritional therapies e.g. garlic

However, there is no evidence available that support the use of these measures.

• Patient education
• Encourage the use of a pain diary.
• Carbamazepine is first line (gabapentin is the alternative) - gradually uptitrate the dose until pain resolves.
• Warn patients of sedative side effects and watch for adverse effects.
• However, the underlying process will continue and pain usually recurs.
• Investigations are only indicated if presence of any other focal neurology - otherwise the diagnosis is clinical.
• If pain resolves then after a period reduce doses of medication with a plan to stop the drug.
• If pain recurs restart or increase the dose.
• If this does not work or the patient is not suitable for drug therapy refer for specialist review.

One third of patients will have mild symptoms and some will only ever have one episode.³ The pain of trigeminal neuralgia can be so intense it can lead to a poor quality of life due to mental and physical incapacity. Patients may require psychosocial input e.g. counselling. Untreated the condition worsens over time and although not fatal a patients life can be severely limited. The episodes become more frequent and more intense with time. At present there is a desperate need for further studies evaluating the role of current treatment modalities.