Treating Trigeminal Nerve Pain
The stabbing, lancinating, recurrent facial pain associated with trigeminal neuralgia (TN) is considered one of the most painful sensations in human experience. It occurs in the distribution of the trigeminal nerve, is of sudden onset, and is excruciating. It can impact mood, sleep, overall health, and employment and, in some cases, has led to suicide.
Management of TN and other types of neurologically based facial pain is best served by a team approach with close communication between neurologists and neurosurgeons, who together can provide various treatment options. Treatment ranges from drug therapy to surgery. Therapeutic success is particularly dependent on differential diagnosis to distinguish classic TN from other types of facial pain, some of which share clinical features with TN.
Differentiating TN from other types of facial pain
TN can occur at any age but is most common after age 50 years, with a higher incidence rate in women than men. Its most distinguishing clinical feature is the nature of the pain. In an effort to elucidate its etiologic features, experts recently subcategorized TN into TN1 and TN2.
TN1, or classic TN, generates repetitive volleys of piercing, paroxysmal pain that can last seconds or minutes and sometimes hours. It is almost always unilateral and typically occurs in the mandibular and maxillary divisions of the trigeminal nerve. TN1 can be triggered by everyday activities that stimulate the nerve, such as eating, speaking, or touching the face.
Pain-free intervals range from several days to years, but typically the pain increases in frequency and severity over time. It is most often caused by vascular compression at the trigeminal nerve root. The redundant looping of an intracranial vessel (typically, an artery) that occurs with aging is thought to create pressure on the trigeminal nerve as it exits the brainstem. In rare cases, the nerve root may be compressed by a tumor, an aneurysm, or an arteriovenous malformation. Over time, demyelination of the nerve due to compression may generate random, spontaneous afferent discharges.
The pain in TN2 is distinguished by a throbbing, burning sensation that is constant rather than episodic. TN2 can arise from various sources, including the following:
- Structural anomalies, such as tumors or arteriovenous malformations
- Inflammatory conditions, such as multiple sclerosis (MS) and herpes zoster
- Trigeminal nerve injury caused by stroke or dental procedures
- Deafferentation arising from intentional denervating procedures used to treat TN1 (eg, anesthesia dolorosa)
Often, TN2 is misdiagnosed as dental pain, for which patients undergo needless tooth extraction. Some patients with TN2 report the shooting pain of TN1 as occurring within a background of chronic dull pain that is more characteristic of TN2. In MS, the symptoms may be the same as in TN1, but the cause is entirely different.
Although demyelinating disease and structural anomalies may be evident on high-resolution MRI, neurovascular compression may not always be seen. For this reason, the clinical examination is critical in determining the best approach to treatment.
Mayo Clinic takes a patient-centered approach in which the patient participates in the decision process leading to treatment. William P. Cheshire Jr., M.D., a neurologist at Mayo Clinic in Florida, says, "We try to bring the pain under control with medication first, but treatment depends on a variety of factors, including age and health status. For example, if medication isn't helping, a patient may be looking at years of intractable pain, so a surgical approach may offer the best long-term option."
Richard S. Zimmerman, M.D., a neurosurgeon at Mayo Clinic in Arizona, adds, "Medication is always the best way to start, but an older patient may be concerned about drug interactions or side effects. However, some patients are anxious to avoid invasive procedures."
Fredric B. Meyer, M.D., a neurosurgeon at Mayo Clinic, notes that patients benefit from working with a neurologist who is willing to try a number of different medications and dosing. "At Mayo," he says, "we are fortunate to have neurologists who specialize in face pain and to have all the medical and surgical options available under one roof."
In TN, the goal of pharmacologic intervention is prevention. TN1 does not respond well to analgesics but does to antiepileptic drugs such as carbamazepine, sometimes at lower doses than those used to treat epilepsy. Usually, pain control can be determined within a few days, but over time the effect may wear off. As Dr. Cheshire notes, dose titration is an art. Incremental dosing helps to prevent dose-dependent adverse effects that might discourage patients from continuing a pharmacologic approach when it could be of great benefit.
Depending on the probable cause of TN, surgical options include microvascular decompression for classic TN1 and percutaneous denervating procedures or stereotactic radiosurgery to block the pain signal. For cases of microvascular compression, surgery directed at the site of compression can stop the pain immediately and have excellent long-term durability.
Percutaneous ablation techniques, such as balloon compression or the injection of alcohol into the nerve (glycerol rhizotomy), are less invasive but also are less durable because the nerve may recover over time.
Stereotactic radiosurgery, another ablative technique, is the least invasive surgical approach, with excellent outcomes.
Motor cortex stimulation is not used for TN1, but it has been found effective for selected cases of intractable trigeminal neuropathic pain arising from deafferentation or previous nerve injury in TN2.