Trigeminal neuralgia is a rare, episodic facial pain that is unilateral, electric shock-like, and provoked by light touch. At first, it is often mistaken as a tooth problem owing to its presentation in the two lower branches of the trigeminal nerve. Patients may undergo unnecessary and sometimes irreversible dental treatment before the condition is recognised.
Trigeminal neuralgia, also called tic douloureux, is a chronic pain condition that affects the trigeminal or 5th cranial nerve, one of the most widely distributed nerves in the head. Trigeminal neuralgia is a form of neuropathic pain, resulting in sporadic, sudden burning or shock-like facial pain. Most cases of trigeminal neuralgia can be managed with anti- neuropathic medications, though in severe cases injection treatment or surgery may need to be considered. Botox injections can be effective in patients with refractory trigeminal neuralgia.
Trigeminal neuralgia is fortunately a rare condition. Data from the United States and validated in the 1990s provided a crude annual incidence of 5.7 per 100 000 women and 2.5 per 100 000 men. Peak incidence lies between age 50 and 60 years, with prevalence increasing with age. General practice databases report an incidence of 27 per 100 000 person years in the United Kingdom.
Women are more at risk than men of trigeminal neuralgia, but the association is not as strong if correction is made for women living longer than men. The strongest association of having trigeminal neuralgia is with multiple sclerosis, which has been seen in both epidemiological data and in data for multiple sclerosis. There may be an association with hypertension and stroke, but this could be due to chance association.
Strong empirical evidence indicates that vascular compression of the trigeminal nerve root is associated with trigeminal neuralgia in about 95% of patients. However, the exact pathophysiology of how vascular compression leads to trigeminal neuralgia remains speculative. Popular hypotheses include a combination of central demyelination of the nerve root entry zone and reinforcing electrical excitability (the ignition hypothesis). Recent studies suggest that this demyelination then leads to an impairment of the nociceptive system. Those patients with more background pain seem to have a loss of central inhibition of the nociceptive system; even after successful surgery, some form of abnormality of somatosensory function remains.
Other factors including predisposing biology on a genetic basis are likely to be important because although rare, familial clusters do exist.
The remaining small subset of trigeminal neuralgia cases are associated with multiple sclerosis plaques or lacunar infarctions within the brain stem trigeminal system or cerebellopontine mass lesions.
The diagnosis of trigeminal neuralgia and other episodic, unilateral neuralgiform pain is based nearly entirely on the history. However, the diagnostic criteria have not been validated by case-control studies and remain based on expert consensus, mainly from headache neurologists and epidemiological studies from the 1990s.
Pain is unilateral in the distribution of the trigeminal nerve, bilateral in only 3% of patients, and rarely is the pain active on both sides at the same time.
Episodic and sudden onset of pain, lasting a few seconds to minutes and stopping suddenly, with many attacks a day. There is a refractory period between each attack. Pain might then go into remission for weeks or months; pain-free intervals gradually shorten between episodes.
Electric shock-like, sharp, shooting
Very severe attacks, but attacks can get milder when patients are given drug treatment.
Can be provoked by light touch to the face, eating, cold winds, or vibrations
Rarely associated with history of other chronic pain or migraine. Some forms have more continued aching background pain after main attack. Rarely associated with autonomic features.
Sensory changes, deafness or other ear problems, difficulty achieving pain control, poor response to carbamazepine, history of any skin lesions or oral lesions that could lead to perineural spread, ophthalmic division only or bilateral as suggestive of benign or malignant lesions or multiple sclerosis, age of onset under 40 years, optic neuritis, family history of multiple sclerosis.
Trigeminal neuralgia often starts suddenly with a memorable onset. The periods of remission tend to get shorter with time and the attacks of pain often get longer; 65% of patients newly diagnosed with trigeminal neuralgia will have a second episode within five years, and 77% within 10 years. Fifty per cent of patients will have remissions of at least six months’ duration. Patients can have as few as three or four attacks a day, but they could have as many as 70 per day. At times the attacks of pain come so quickly that it is impossible to determine whether there is a gap between each attack. There is often a refractory period when the pain cannot be triggered. Pain can occur at night in a third of patients. It is unusual to have trigeminal neuralgia in the first ophthalmic division of the trigeminal nerve only.
Some patients continue to have a background pain of lower intensity for 50% of the time. This condition has variously been called atypical trigeminal neuralgia, type 2 or—in the new International Classification for Headache Disorders—trigeminal neuralgia with concomitant persistent facial pain. Some patients might also have autonomic features such as conjunctival injection, lacrimation, nasal congestion or rhinorrhoea, eyelid oedema, ptosis, or facial sweating. In the presence of autonomic symptoms, it can be difficult to determine whether this is still trigeminal neuralgia or a variant known as short unilateral neuralgiform pain with autonomic symptoms (SUNA) or short unilateral neuralgiform pain with conjunctival injection and lacrimation (SUNCT).
Trigeminal neuralgia itself is a purely clinical diagnosis. However, investigations could be required especially if red flags are present. These investigations are targeted towards identifying other craniofacial pain syndromes within a differential diagnosis of trigeminal neuralgia and identifying non-vascular compressive causes of trigeminal neuralgia.
The most useful investigation is an MRI scan of the brain with and without contrast, which is used to rule out other potential causes of pain if the diagnosis is not clear cut or if red flags are present.
MRI is the most sensitive screening and diagnostic test available for detecting multiple sclerosis and has the highest positive predictive value. Although rare, brain tumours can be associated with trigeminal neuralgia. Posterior fossa tumours are the tumours most likely to be associated with typical trigeminal neuralgia pain characteristics, and are most commonly vestibular schwannomas, meningiomas, or epidermoid cysts.
Anti neuropathic drugs are the mainstay of management in trigeminal neuralgia. Carbamazepine remains the drug of choice, though this is based on small randomized controlled trails of poor quality. However incidence of side effects, is high , mainly central nervous system effects such as tiredness and poor concentration and there is a high risk of drug interactions. The second drug of choice is oxcarbazepine, a keto derivative of carbamazepine that has shown similar efficacy to carbamazepine but increased tolerability and fewer drug interactions.
Carbamazepine should be started at 100 mg up to twice daily, and titrated in steps of 100 – 200 mg every two weeks, until pain is relieved. In the majority of people a dosage of 200 mg three or four times a day is sufficient to prevent paroxysms of pain (maximum dosage 1,600 mg daily). Modified release preparations may be useful at night if the person experiences breakthrough pain. Once pain is in remission, the dosage should be gradually reduced to the lowest possible maintenance level, or the drug can be discontinued until a further attack occurs.
Do not prescribe carbamazepine to people:
Prescribe carbamazepine with caution to people:
Common adverse effects of carbemazepine include nausea and vomiting, sedation, dizziness, and ataxia.
Other drugs that have been used in management of trigeminal neuralgia include:
Microvascular decompression. This procedure involves relocating or removing blood vessels that are in contact with the trigeminal root to stop the nerve from malfunctioning. Microvascular decompression can successfully eliminate or reduce pain most of the time, but pain can recur in some people. Microvascular decompression has some risks, including decreased hearing, facial weakness, facial numbness, a stroke or other complications. Most people who have this procedure have no facial numbness afterward.
Brain stereotactic radiosurgery (Gamma knife). In this procedure, a surgeon directs a focused dose of radiation to the root of your trigeminal nerve. This procedure uses radiation to damage the trigeminal nerve and reduce or eliminate pain. Relief occurs gradually and may take up to a month.Brain stereotactic surgery is successful in eliminating pain for the majority of people. If pain recurs, the procedure can be repeated. Facial numbness can be a side effect.
Radiofrequency lesioning of trigeminal nerve and glycerol injection can also be used in management of trigeminal neuralgia.
Botulinum toxin type A (BTX-A) has been reported to have analgesic effects independent of its action on muscle tone, mostly by acting on neurogenic inflammatory mediators and controlling the neurotransmitter release of sensory and autonomic nerve terminals that are involved in many chronic painful conditions as chronic intractable trigeminal neuralgia.
The analgesic effect of BTX-A has been investigated through a series of open-labeled studies as well as a few randomized controlled trials (RCTs), with an increasingly strong evidence that botulinum toxin injections are efficacious, thus placing it as a treatment option either before surgery or for those with intractable trigeminal neuralgia and unwilling to undergo surgery, however, a more placebo-controlled clinical trials are still needed to confirm these findings.
The role of BTX-A in the treatment of drug-refractory trigeminal neuralgia has been evaluated by some authorities and it was found to be an effective treatment with the majority of the patients reporting a reduction or even disappearance of the pain. BTX-A was found to be effective in combination with pharmacotherapy, prior to considering more invasive therapies such as surgery or gamma knife radiosurgery. As such, BTX-A is a particularly valuable treatment for elderly patients and those with adverse anesthetic comorbidities. However, these studies included small patients number or of low-quality RCTs.
The mechanism by which BTX-A exerts its antinociceptive effect is poorly understood; whether or not BTXA can change sensory perception in those patientsremains unknown. Cui et al demonstrated that subcutaneous BTX-A injection is associated with the inhibition of formalin-induced glutamate release; an important mediator for the induction and maintenance of central sensitization of pain. BTX-A may also reduce the peripheral nociceptive input by inhibiting the release of substance P and calcitonin-gene-related peptide (CGRP), both of which would play a very important role in neurogenic inflammation. Moreover, BTX-A can reduce the release of other neurotransmitters and neuromediators including epinephrine and norepinephrine.
Regarding safety of BTX-A, injection-related side effects have been reported: facial asymmetry and edema/ hematoma at the site of injection, both of which are generally well tolerated and transitory in nature. Overall botox injections are well tolerated and any side effects are transient.