What is trigeminal neuralgia?
Trigeminal neuralgia (TN) is one of the most common, and also the most well-defined causes of facial pain. It tends to affect females slightly more than males, and increases slightly with age. Generally, the attacks worsen over time, and the latent periods become more infrequent and shorter.
What causes trigeminal neuralgia?
Compression of the trigeminal nerve root is the recognized cause of trigeminal neuralgia most of the time. 80-90% of the time it is the abnormal loop of an intracranial artery, or less commonly, vein, that compresses the nerve root close to the location where it enters the brainstem.
Other causes of compression are tumors, epidermoid cyst, or aneurysm. The compression then leads to damage of the protective covering of the nerve, called myelin. As a result, the nerve acts in an erratic manner, causing pain signals to be sent sporadically at the trigger of light touch, chewing, or brushing the teeth.
Rarely, traumatic injuries of the trigeminal nerve, such as a car accident, can lead to similar damage. In multiple sclerosis, loss of myelin in one or more of the trigeminal nerve nuclei can also cause trigeminal neuralgia.
Diagnosis of trigeminal neuralgia is made clinically based on the above-mentioned features. The physician may also order radiological imaging depending on his clinical suspicion and the history obtained. Diagnostic criteria for classic trigeminal neuralgia are:
- Paroxysmal attacks of pain lasting from a fraction of a second to two minutes, affecting one or more of the subdivisions of the trigeminal nerve
- Pain has at least one of the following characteristics: 1) Intense, sharp, superficial, or stabbing or 2) precipitated from trigger areas or by trigger factors
- Attacks are stereotyped in the individual patient
- There are no clinically evident neurologic deficits
- Not attributed to another disorder
TN is defined by the International Association for the Study of Pain (IASP) as sudden, usually unilateral, severe, brief stabbing or lancinating, recurrent episodes of pain in the distribution of one or more branches of the trigeminal nerve. Less often, patients may have a constant aching or burning sensation most of the time. A tingling sensation or aching may also precede the pain episodes. Vibration or contact with the face may trigger the intense flashes of pain.
The attacks usually last several seconds to a couple of minutes and repeat over the subsequent hours to weeks. The episodes then disappear for months to years before recurring. It can be bilateral, but does not involve both sides simultaneously. Rarely does the pain occur at night when the patient is sleeping.
The standard medical approaches to treating trigeminal neuralgia are anti-inflammatory, anticonvulsant, and antidepressant medications. After these fail, local anesthetic blocks are attempted, but they only provide temporary pain relief. Lastly, percutaneous or open procedures (such as those listed below) may be done, or even more rarely, neurostimulation:
- Microvascular decompression: An invasive procedure involving removal or separation of vasculature, which is often the superior cerebellar artery, away from the trigeminal nerve.
- Balloon compression: A balloon catheter is inflated and used to compress the gasserian ganglion.
- Gamma knife radiosurgery: A noninvasive treatment that creates lesions by using focused gamma radiation. The radiation is targeted at the proximal trigeminal root with the aid of stereotactic frame and MRI.
- Electrolytic rhizotomy: A percutaneous procedure that creates a lesion in the gasserian ganglion of the trigeminal nerve by using the heat of radiofrequency.
- Linear accelerator radiosurgery: A noninvasive approach similar to gamma knife, but uses a different form of radiation, linear acceleration.
- Peripheral neurectomy: An incision, radiofrequency lesioning, alcohol injection, or cryotherapy is used on a peripheral branch of the trigeminal nerve.
- Chemical rhizotomy: An injection of glycerol into the trigeminal cistern. Tingling or burning is felt in the face, and pain relief is usually immediate, but may take up to a week.