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|First detailed in the 18th century, trigeminal neuralgia is a severe, lancinating pain in the trigeminal nerve territory that can be triggered by various stimuli (e.g. touch).
Diagnostic criteria for idiopathic trigeminal neuralgia by the International Headache Society are as follows:
Paroxysmal attacks of facial or frontal pain occur, lasting a few seconds to less than 2 minutes.
Pain has at least four of the following characteristics:
- Distribution along one or more divisions of the trigeminal nerve
- Sudden, intense, sharp, superficial, stabbing or burning in quality
- Severe pain intensity
- Precipitation from trigger areas or by certain daily activities (e.g. eating, talking, washing the face, cleaning the teeth)
- No symptoms between paroxysms
No neurological deficit is present.
Attacks are stereotyped in the individual patient.
Other causes of facial pain are excluded by history, physical examination and special investigations (when necessary). In symptomatic cases, a persistence of aching can occur between paroxysms, as well as signs of sensory impairment in the trigeminal division. Then, a cause is demonstrated by appropriate investigation.
Trigeminal neuralgia is the prototype of neuropathic pain, meaning that the pain mechanisms themselves are altered. Evidence of both small and large fibre damage is present, as suggested by the potential for vibration to trigger an attack. Demyelination of the nerve, primary or secondary, leads to uncontrolled firing of small unmyelinated trigeminal nerve fibres. This occurs, in part, because of the lack of inhibitory inputs from large myelinated nerve fibres. However, features also suggest a partly central mechanism (e.g. delay between stimulation and pain, refractory period). The central abnormalities are still poorly understood.
Prevalence is approximately 1.5 cases per 10,000 population. Although a questionable family clustering exists, trigeminal neuralgia is most likely to be multifactorial.
No geographical tendency exists.
Mortality is virtually non-existent; however, the severity of the pain may lead to suicide.
No racial differences regarding this disease have been reported.
Females are affected twice as often as males.
Most cases develop in patients older than 50 years, but occasional reports of paediatric cases indicate a large range of age at onset.
Although it may be interrupted by remissions of a few months, trigeminal neuralgia is a long-term condition, consisting of episodic headache. This disease has the typical characteristics of neuropathic pain.
• The pain is lancinating and hardly lasts for longer than a second. Because multiple bouts frequently follow each other, the patient often misleadingly describes a continuous pain. A refractory period that can be as short as a couple of seconds occurs. The intense pain is followed by a bothersome sensation in the area. If prominent, the painful sensation is indicative of a potential underlying lesion (e.g. tumour) in the posterior fossa.
• In most cases, pain is located in V3 or V2; it is located rarely in both and exceptionally in V1. Pain is unilateral and does not shift sides. Although very rare, bilateral cases have been described.
• Different stimuli can trigger pain, often consistent in each patient. These stimuli include the following:
- Touching or applying heat or cold to the cheek or gum
- Chewing, yawning or talking
- Wind blowing in the face
- Gustatory stimuli and vibration
Physical: Except for a trigger zone, usually in the face, general and neurological examinations should be normal. Although they may be observed for a short time in idiopathic trigeminal neuralgia, hypaesthesia or dysaesthesia in the face should be considered part of the secondary forms.
Causes: Trigeminal neuralgia is divided into two categories, idiopathic and secondary.
Secondary forms can have multiple origins:
- Acoustic neuroma
- Chordoma at the level of the clivus
- Pontine glioma
- Pontine infarct
- Arteriovenous malformation in the vicinity
- Persistence of a primitive trigeminal artery
- Pulsatile compression by the adjacent superior cerebellar artery (more rarely, antero-inferior artery)
- Multiple sclerosis
- Lyme disease neuropathy
Cluster headache: Pain is not restricted to a branch of the trigeminal nerve but is periocular, lasts longer (15-120 min), is not triggerable, is accompanied by prominent autonomic symptoms and usually has fewer episodes per day.
Raeder syndrome: Ophthalmoparesis is present.
Atypical facial pain: In addition to pain that is of vague localisation and long duration (usually chronic and daily), psychiatric disturbances are associated.
Tolosa-Hunt syndrome: Pain is of longer duration but not triggerable.
Dental abscess, sinusitis, and sinusal adenocarcinoma are possible differential diagnoses.
Imaging studies Imaging studies are indicated because distinguishing between idiopathic and secondary forms of trigeminal neuralgia is not always clear.
CT scan provides a poor resolution in the posterior fossa.
MRI is the imaging modality of choice. It can reveal multiple sclerosis plaques and pontine gliomas.
Magnetic resonance angiography (MRA) can be useful in locating a vascular compression; however, the sensitivity remains low.
Newer techniques, with enlarged views on the pontine area, can demonstrate a neurovascular conflict (e.g. postero-inferior cerebellar artery compresses the trigeminal root).
Conventional angiogram is only useful if a vascular malformation is suspected, but it fails to demonstrate directly the relationship with the nerve.
Clinical neurophysiology testing with a blink reflex study may be helpful to demonstrate a lesion of the trigeminus in which a bilateral delay occurs in response to the stimulation on the pathological side. The blink reflex should be normal in the idiopathic form of the syndrome.
Histological findingsAlthough not a diagnostic test, histological findings reveal focal demyelination as the ultimate lesion in both secondary and idiopathic cases. In secondary cases, the underlying lesion can be assessed by histology in some instances (e.g. tumour).
Treatment can be subdivided into pharmacological therapy, percutaneous procedures, surgery and radiation therapy. Most patients respond well to initial therapy, but some are resistant to any type of treatment. Treatment must be tailored individually, based on the patient's age and general condition. In the case of secondary trigeminal neuralgia, adequate treatment is that of its cause.
Carbamazepine was introduced in the 1960s and has proven its efficacy in numerous studies. It remains the criterion standard of treatment for this condition.
Phenytoin has a lower rate of success, but a patient occasionally responds to it and not to carbamazepine. The dose varies greatly among patients.
Baclofen has proven efficacy in this condition.
Clonazepam has moderate efficacy but is not recommended because of its adverse effects (e.g. sedation) and dependence.
Amitriptyline has been used, but the success rate is low.
Gabapentin seems to be effective, but as of yet no controlled study is available.
Lamotrigine has been proven more effective than placebo. The dosage should be increased slowly for better tolerance (e.g. 25 mg daily dose each week; up to 250 mg twice a day).
Jannetta pioneered microvascular decompression (MVD). This procedure consists of opening a keyhole in the mastoid area and freeing the trigeminal nerve from the compression/pulsating artery; then, a piece of Teflon is placed between them. Large series have been published, and the initial efficacy is more than 80%. Recurrence rates are among the lowest compared with other invasive treatments. Usually, it requires the demonstration of true contact and compression by the artery on the nerve, but series are published that show an almost equally effective result without any demonstrated abnormality on imaging or even frank compression shown preoperatively.
Alcohol injection of the trigeminus can be performed at various locations along the nerve and is aimed at destroying selective pain fibres. Although it is an easy procedure, the success rate is low, in part because of a low selectivity of effect on the fibre type with this substance.
Glycerol injection of the gasserian ganglion to destroy selectively the pain-transmitting fibres has been used for a long time. This injection has a higher efficacy rate and a lower recurrence rate than the alcohol injection.
Percutaneous radiofrequency rhizotomy and percutaneous microcompression with balloon inflation are relatively inexpensive accessible techniques and are less invasive than surgery, with a lower (long-term) efficacy-to-recurrence ratio.
Recently introduced, gamma-knife treatment consists of multiple rays (over 200) of high-energy photons concentrated with high accuracy on the target (i.e. trigeminal nerve root). This treatment destroys specific components of the nerve. Of those treated, 60% of patients are pain free immediately, and more than 75% of patients have greater than 50% relief after 1.5 years. This treatment can be used after a patient's failure to respond to any of the above-mentioned procedures, including this one. The device contains a stable source of radiation (60-Co), which frees this technique from requiring an external source of radioactivity (e.g. cyclotron).
Preliminary reports of pulsed radiofrequency on the trigeminal ganglion may be a promising new option.
Other than avoiding the triggers, the activity of the patient should remain normal.
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