The Trigeminal Nerve
The human nervous system is divided into the central nervous system (CNS) and the peripheral nervous system (PNS). The CNS is divided into the brain and the spinal cord. Exiting from the brain are twelve pairs of nerves named the cranial nerves. Most of the cranial nerves have motor and sensory functions in the head and neck region. The trigeminal nerve is the fifth cranial nerve and its normal function is to transmit sensory information from the facial region including the the jaws and teeth. In addition it has motor functions innervating the chewing muscles and some muscles in the pharynx and the middle ear. It does not innervate the mimic muscles of the face, this is done by the seventh cranial nerve.
The trigeminal nerve has three main divisions (this is the reason for its name). The first branch, also called the ophtalmic nerve, is responsible for sensory information above the eyes reaching approximately to the vertex of the skull. The second branch, the maxillary nerve, is responsible for the area below the eyes, the nose and the upper jaw (including teeth). The third branch, the mandibular nerve, responds for the lower jaw (including the teeth), the tongue and the temporal region. The third branch also has motor functions. The trigeminal nerve is not responsible for the movements of the tongue and not for taste.
Trigeminal Neuralgia
Trigeminal neuralgia is more common in temperated zones than in subtropical or tropical areas. It is somewhat more common among women than men and it is more common after the age of 50. A person with multiple sclerosis (MS) is more likely to suffer from trigeminal neuralgia than a person who do not have MS.
Classical Trigeminal Neuralgia
Classical trigeminal neuralgia, or tic douloureux, is characterized by extremely intense bursts of pain in the facial region (cheek, nose, lips, jaw, forehead, mouth, tongue). The bursts are usually of a short duration (seconds) but may in rare cases last in the minute range. Common triggers of TN attacks are eating, talking, tooth brushing and touching, but attacks may occur also without any triggering stimulus. Patients may describe the pain as if somebody pressed a 100000 volt cable against the cheek or as if somebody hit them with an axe in the face. When it occurs, an attack is strictly localized to one side of the face and may involve one, two or all three branches. However, the second and third branch are more commonly affected than the first branch. In the typical case there is no pain between the attacks. Occasionally, patients with multiple sclerosis has a bilateral disease. TN may be less severe for some months and then come back with equal or worse strength. In severe cases the patient has so frequent attacks that she needs intensive care due to malnutrition.
MS-associated Trigeminal Neuralgia
As mentioned above, patients with MS are more likely to have trigeminal neuralgia then patients who don't have MS. In contrast to the classical type, MS-associated trigeminal neuralgia may affect both sides of the face. MS-associated trigeminal neuralgia does not respond so well to medication as the classical type and often the MS-patient deteriorates in other symptoms due to the strong medication.
For practical clinical purposes, and particularly selecting patients for surgery, it is important to identify the classical type and the MS-associated type. Only these two types are usually considered for trigeminal neuralgia surgery (other types of surgery, such as deep brain stimulation, peripheral nerve stimulation, motor cortex stimulation or magnetic resonance guided focused ultrasound (MRgFUS) may of course be considered but this falls beyond the scope of this presentation.
Diagnosis
The diagnosis of TN is easy in the classical case, i.e. when patients present the characteristic symptoms described above: intense one-sided bursts in trigeminal nerve innervated locations and pain free periods in between. There are no blood tests, X-rays, CT-scans or MRI scans that can help the physician. If the patient responds well to a comparatively low dose of karbamazepin or oxcarbazepin the diagnosis is more or less certain. If the patient has effect from ordinary pain-killers, non-opioid or opioid, it contradicts the diagnosis. Bilateral bursts or bursts in locations that are not innervated by the trigeminal nerve strongly contradicts the diagnosis as does constant pain. However, as always, there are grey zones and sometimes the diagnosis is difficult.
Medical treatment
Treatment for trigeminal neuralgia is primarily medical (pharmacological). The most efficient drugs are karbamazepin and oxkarbazepin. These drugs are normally used for the treatment of epilepsy and it is not entirely clarified why they are so efficient in the treatment of TN. If the neuralgical bursts disappears promptly on one of these drugs this means that the diagnosis is certain. Unfortunately these drugs may give rise to severe non-wanted side effects and other, usually less efficient, drugs must be tried. These include other anti-epileptics, antidepressants and pain-killers. Usually the disease does not respond to pain-killers, neither opioids nor non-opioids.
Surgical options for trigeminal neuralgia
A patient with TN who responds well to medication and where the side effects are tolerable should of course not be operated. Surgery is actualized when the doses cannot be increased any further because of side effects, and when the patient still suffer from severe pain attacks. In principle, surgery fall into four categories:
(i) open neurosurgery, so-called microvascular decompression or MVD,
(ii) percutaneous procedures where the trigeminal ganglion is reached with a cannula through the cheek,
(iii) stereotactic radiation towards the proximal portion of the trigeminal nerve and
(iv) injections towards peripheral branches.
Which surgical option is then the best? Well this has been a question of much discussion. So called Kaplan-Meyer plots are helpful for the evaluation of long-term results.
Contact
I hope this site has been helpful for you. If you wish to contact me for further information on trigeminal neuralgia and the treatment options please fill in the contact form below. Since 1997 I have met about 3000 patients with facial pain and performed about 1300 operations.