Trigeminal Neuralgia

Trigeminal Neuralgia

Trigeminal neuralgia (TN), also known as tic douloureux, is a chronic neurological condition characterised by sudden, severe facial pain. It is often described as a “lightning bolt” striking the face by patients. It involves the trigeminal nerve, as the name suggests, which is the fifth and largest cranial nerve. The trigeminal nerve has both sensory and motor components which provide sensation to the face and motor innervation to the muscles of mastication. In trigeminal neuralgia, one of the nerves (unilateral involvement) is affected – with one or more branches being involved. In a nutshell, most cases of TN are due to compression of the trigeminal nerve root within a few millimetres of its entry into the pons or along its distal course. The International Association for the study of Pain describes TN as , ’sudden, usually unilateral, severe, brief, stabbing, recurrent episodes of pain in the distribution of one or more branches of the trigeminal nerve.’ TN is a diagnosis that can be established clinically. Investigations are done to rule out possible causes of facial pain.

Majority of those affected are over 50 years of age and female (cause unknown). Peak ages for diagnosis are between 60-70 years of age. TN is frequently right-sided (59% of cases) and is usually limited to one branch, of which the maxillary branch was the most commonly affected though simultaneous involvement with the mandibular branch is not uncommon.

According to the International Clasification of Headache disorders the causes of TN can be classified into:

Based on presentation we can classify TN into:

• Examples of space occupying lesions that could cause trigeminal neuralgia
  • Meningioma
  • Acoustic neuroma
  • Epidermoid cyst
  • Arterio-venous malformations
  • Saccular aneurysms
• Risk factors for trigeminal neurlagia
  • Multiple sclerosis
  • Hypertension
  • Old age
  • Atherosclerotic vascular changes
  • Positive family history – genetic transmission occurs in 1-2% of cases
  • Intense stress
• Pathophysiology
  • TN is one of the most common cause of craniofacial neuropathic pain. Despite its severity, the exact mechanism is unknown. It is thought that the compressive pressure on the root of the trigeminal nerve by neuro-vascular structures or space occupying lesions may be the mechanism behind such pain.
  • Compression causes focal demyelination, atrophy of the peripheral axons and Schwann cells as well as displacement of nerve fibres leading to misfiring of nervous signals causing the severe pain patients report.
  • There is also evidence that voltage gated sodium channels are damaged during the insult leading ectopic firing of signals from dysregulated neurons.
• Triggers of pain in trigeminal neuralgia
  • Chewing
  • Talking
  • Smiling
  • Drinking cold or hot fluids
  • Touching
  • Shaving
  • Brushing teeth
  • Blowing the nose
  • Encountering cold air
• Signs and symptoms
  • Severe facial pain localised to the trigeminal nerve distribution: cheek, upper and lower jaw, lips (few complain of pain along the scalp and forehead as the ophthalmic branch is usually spared)
    • Pain is triggered by movement (even routine activities, causing limitations)
    • Sensation of electric shock in the affected area
    • Fades within seconds leaving a burning ache that lasts seconds to minutes
    • Attacks provoke the patient to grimace, wince, or make and aversive hence movement as if trying to escape the pain (hence the term ‘tic doloureux’)
• Physical examination
  • Ipsilateral eye may appear watery and red
  • Facial muscle contraction when pain is elicited (tic)
  • Rhinorrhoea
  • Excessive lacrimation
  • Sensory loss and facial muscle weakness may indicate secondary causes of trigeminal neuralgia
• Differentials
  • Dental pain
  • Sinus related pain
  • Post herpetic neuropathy
  • Temporal mandibular joint dysfunction
  • Facial myalgia
  • Cluster headaches
  • Giant cell arteritis
• Diagnostic criteria for trigeminal neuralgia (International Classification of Headache Disorders)
  • A – Pain has all of the following characteristics:
    1. Lasting from a fraction of a second to two minutes
    2. Severe intensity
    3. Electric shock-like, shooting, stabbing or sharp in quality
  • Precipitated by innocuous stimuli within the affected trigeminal distribution
  • Not better accounted for by any other ICHD-3 diagnosis
• Investigations
  • MRI and CT scan of the head and neck: to detect secondary causes (tumor or multiple sclerosis)
• Medical treatment
  • Carbamazepine: 100mg every 6 hours. Can take 1200mg/day if necessary
  • Oxcarbazepine: Has more recently become first line treatment. Can be used in patients who cannot tolerate carbamazepine
  • Other medications: gabapentin, baclofen, amitriptyline, pregabalin, phenytoin, valproic acid, clonazepam, sodium valproate, lamotrigine, topiromate, and opiods
• Surgical treatment
  • Microvascular decompression (Janetta procedure): exposure of the trigeminal nerve root and identification of the vessels compressing the nerve. The vessel is gently moved from the point of compression.
  • Lesioning procedures e.g. percutaneous radiofrequency rhizotomy, percutaneous balloon compression, percutaneous glycerol rhizotomy, and stereotactic radiosurgery (gamma knife), peripheral neurectomy and nerve block
• Prognosis
  • May remit for months or years after initial attacks
  • Sensory deficits and bilateral distribution are better clinical prognostic indicators
  • Young age is a moderate predictor
  • Lack of therapeutic response and Ophthalmic (V1) distribution are poor predictors
• Complications
  • Anaesthesia dolorosa: intractable facial dysesthesia that may by more disabling than the original trigeminal neuralgia. May be caused by procedures.
  • Brain tumor
  • Bone marrow aplasia
  • permanent loss of sensation over a portion of the face or mouth
  • Jaw weakness
  • Corneal ulceration
  • Corneal anaesthesia
  • Reactivation of herpes simplex following invasive treatment