Trigeminal neuralgia (TN) refers to a type of neuropathic pain caused by damage to the trigeminal nerve, which is responsible for transmitting signals from the face to the brain. It is defined as sudden paroxysmal electric shock-like pain in the face that is brief in onset and cessation, and usually unilateral. It occurs in recurrent episodes and is limited to the distribution of one or more of the trigeminal nerve branches responsible for sensations in the head1:
These painful paroxysms may occur many times a day and can last from a fraction of a second to 2 minutes, with refractory periods of no pain in between in about 50% of patients. The other half of TN patients will experience continued pain of lower intensity in the same distribution2.
TN can be triggered by things as simple as light touch of the affected area, talking or chewing, and brushing teeth. Stimulus-dependence is considered one of the most striking characteristics of TN and a criterion of clinically established TN.3 It can be classified into the following three categories3,4:
TN is one of the most common neuropathic pain syndromes in people with MS and can greatly affect their quality of life, increasing the prevalence of anxiety, depression and sleep disorders in affected patients5. People with MS have an approximately 20 times greater risk of TN relative to the general population, with an estimated 3–5% experiencing the painful symptom, without differences between relapsing-remitting, secondary and progressive forms6-8. Although the underlying mechanisms have not been completely explained, damage to the myelin sheath that protects the trigeminal nerve is thought to be at the root of the pain sensations in people with MS9. Sometimes, a blood vessel pressing on the nerve can cause trigeminal neuralgia.
TN secondary to MS is more common in women than in men, and affects the right side more frequently than the left side10. Although the characteristics of TN secondary to MS are similar to those observed in classical TN, the pain is more frequently bilateral in people with MS, with an estimated 18% of patients reported to have bilateral TN.
Classical or idiopathic TN can be treated with medications, usually starting with carbamazepine or other sodium-channel blockers. Another commonly used medication is baclofen. It relaxes the muscles to help ease the pain. If pharmacologically derived treatments fail, patients are generally referred to neurosurgery to discuss gamma knife, rhizotomy or vascular decompression11.
Guidelines for treating MS-associated TN have not been well established. According to international guidelines, there is insufficient evidence to support or refute the effectiveness of any medication in treating pain in TN secondary to MS12. It is generally agreed that the first line therapy is pharmacological and based on the use of sodium-channel blockers and oxcarbazepine. Gabapentinoids and antidepressants might be more effective in persistent than in paroxysmal pain and are often tried as an add-on to oxcarbapezine or carbamazepine in people with the atypical form of TN with concomitant persistent pain13.
Available data indicate that medications are poorly tolerated in people with MS, and can possibly exacerbate existing symptoms of the neurodegenerative disorder14. It is also becoming increasingly recognised that people with MS and TN can become medically refractory to treatment and increasingly require surgical intervention for pain management15.
A multidisciplinary care pathway for these patients has been proposed which is the same as for classical TN16. This pathway has been shown to result in significant improvement in global impression of change and includes support from clinical nurse specialists and psychology support to help patients live well with pain and uncertainly17,18.
In summary, people with MS experiencing TN face many challenges in achieving pain control in relation to their condition. Enabling the person to be well informed regarding pharmacological and surgical options available via joint discussions with physicians and neurosurgeons ensures they are empowered to make the right decision for their individual care.
