While nonfatal, trigeminal neuralgia (TN) is among the most painful and disabling of all medical conditions. Despite its dreadful symptom of lancinating, shock-like facial pain, trigeminal neuralgia can also be highly treatable. However, the disease must be carefully differentiated from the plethora of other causes of facial pain, and the correct treatment protocol must be applied in the case of a given patient.
Initial evaluation of trigeminal neuralgia: Patient history
While patients typically arrive at our center with a presumptive diagnosis of trigeminal neuralgia, there is great variation among patients’ histories. Some arrive having been just recently diagnosed while others have faced years of uncertainty, having been shuttled between a number of healthcare professionals before being referred for surgical evaluation. Still others present to our center with a history of unsuccessful treatment attempts.
Regardless of a particular patient’s history, the goals of the initial evaluation are always the same. The first goal is to confirm that the pain is indeed consistent with trigeminal neuralgia and to exclude other possible causes. Secondly, the initial assessment is designed to determine whether the patient is an appropriate candidate for a surgical procedure and, if so, to predict the likelihood of a successful outcome.
Trigeminal neuralgia pain occurs exclusively within one or more of the trigeminal nerve’s three distributions on one side of the face. Most patients experience initial pain relief upon taking an anticonvulsant medication such as carbamazepine, although the effects of such medications tend to diminish with time. Trigeminal neuralgia can be subdivided according to the Burchiel scheme into trigeminal neuralgia types 1, 2a, and 2b. Such classification is important because it is predictive of surgical success.
Patients with type 1 TN experience a memorable onset of symptoms often described as a “lightning-bolt of pain that came out of nowhere.” The pain, while severe, tends to last for only seconds at a time and may occur many times per day. Even though attacks become more frequent, the pain is always shock-like and never constant or dull. Although attacks often occur spontaneously, patients with type 1 TN usually report certain triggering factors such as cold wind, eating, drinking, or using a washcloth. Additionally, patients with type 1 TN tend to have spontaneous remissions of symptoms lasting days to weeks early in the course of the disease with these pain-free intervals becoming shorter and less frequent as time passes. Patients with type 1 TN have the most favorable outcomes following any treatment modality.
In contrast, patients with type 2b trigeminal neuralgia have a more insidious onset of pain. Rather than experiencing a “lightning bolt out of nowhere,” patients may initially believe that they have a tooth or sinus ache for many months before the pain is determined to be neurologic. The pain is often described as being dull, boring, constant, aching, or throbbing. Like type 1 trigeminal neuralgia, the symptoms are extremely disabling. The prognosis following surgical treatment of patients with type 2b trigeminal neuralgia is less favorable than in patients with type 1 trigeminal neuralgia. However, patients who respond favorably to anticonvulsant medication may still benefit from an operation.
Type 2a trigeminal neuralgia is the diagnosis applied to patients who have type 1 symptoms early in the disease course and transition, over time, to a more constant pain consistent with type 2b trigeminal neuralgia. The outcomes of these patients following a surgical treatment is thought to be more favorable than in patients with type 2b trigeminal neuralgia but less favorable than in patients with type 1 trigeminal neuralgia.
Initial evaluation of trigeminal neuralgia: objective testing
While the diagnosis of TN is often considered to be “clinical,” meaning that it is based solely on a patient’s symptoms and medical history, there are several objective tests that can help confirm the diagnosis and determine the correct treatment plan. All patients with TN-like pain should undergo contrast-enhanced magnetic resonance imaging in order to rule out multiple sclerosis and structural anomalies such as a tumor, Chiari malformation, or vascular malformation. Treatment of patients with confounding diagnoses requires treatment of the primary disorder.
Additionally, all patients at our center undergo a specially protocoled thin-slice MRI with heavy T2 weighting. This type of scan is optimized to view the cranial nerves and surrounding vasculature. Our center has worked closely with the neuroradiology faculty in order to improve the sensitivity and specificity of this type of imaging and in order to determine how to best combine this information with a patient’s clinical presentation in order to aid in diagnosis and preoperative planning. A recent blinded-study conducted at the center revealed that this type of imaging has high sensitivity for detecting neurovascular compression.
Selection of a treatment option
The first-line treatment in all patients with trigeminal neuralgia is medication. Because opioids and non-steroidal anti-inflammatory medications are ineffective against neuropathic pain, anticonvulsant medications are employed. The most commonly effective drug is carbamazepine (Tegretol) but other choices may include gabapentin (Neurontin), phenytoin (Dilantin), pregabalin (Lyrica), oxcarbazepine (Trileptal), and baclofen (Lioresal). While some patients may find that medical therapy brings their symptoms under satisfactory control, many patients find that their pain either becomes refractory to medication or requires increasing medication doses, over time. Eventually the side effects of medication, such as lethargy, may become intolerable.
Microvascular decompression is an operation that directly treats the cause of trigeminal neuralgia by moving any compressive blood vessels off the centrally-myelinated portion of the trigeminal nerve. Because it is the only treatment that addresses the direct cause of trigeminal neuralgia, it has the lowest risk of trigeminal sensory side effects and the lowest annual recurrence rate (<1% per year).
Due to our high-volume experience with MVD and the use of a dedicated team, our MVD patients are able to proceed directly to a regular hospital nursing unit instead of the intensive care unit after surgery. In fact, a recent retrospective review showed that our patients had a median hospital stay of only two days. There was no difference in length of stay between younger and elderly patients. Additional features of MVD performed at the University of Pittsburgh include intraoperative neuromonitoring by an experienced team of electrophysiologists and the combined used of intraoperative microscopy and endoscopy.
Ablative procedures for trigeminal neuralgia involve the partial destruction of the trigeminal nerve such that normal sensory function is maintained while preventing aberrant painful sensations from traveling through the nerve. Ablative treatments for TN include percutaneous glycerol rhizotomy and percutaneous radiofrequency rhizotomy, which are needle-based procedures performed on an outpatient basis with the use of local anesthesia and sedation. This category of treatments also includes stereotactic radiosurgery (e.g. Gamma Knife ®), which uses radiation to selectively damage the nerve.
Because these treatments work by damaging the trigeminal nerve, the rate of sensory side effects such as numbness and painful dysesthesias is higher than in microvascular decompression. Additionally, these destructive procedures are less long-lasting than microvascular decompression and often must be repeated every several years in order to maintain pain relief. With each repeated procedure, the chance of bothersome sensory side effects increases. When choosing an ablative procedure, UPMC Center for Cranial Nerve and Brainstem Disorders usually recommends glycerol rhizotomy because it is less likely to induce sensory changes in the trigeminal nerve.
Although we recommend MVD as a first-line treatment in most patients, glycerol rhizotomy does have a place in our repertoire. We routinely perform this procedure in patients who are too infirm to tolerate a major neurosurgical operation, patients with a life expectancy of less than two years, and patients with symptomatic trigeminal neuralgia (i.e. a diagnosis of both TN and multiple sclerosis).
Areas of particular expertise and study
MVD in the Elderly
Even in recent years, some physicians have been hesitant to suggest that MVD be performed in elderly patients because the operation was thought to be riskier in patients over the age of 65 years. However, our center has published both original research and a systematic review of the literature showing no difference in outcomes or complications after MVD for TN in elderly patients. Because a 70 year-old patient with TN may live for another 20 years, performing an ablative procedure which may have to be repeated every two years, with an increased risk of bothersome side-effects each time, is sub-optimal. Consequently, we offer MVD as a first-line treatment to patients who meet the clinical criteria and who are healthy enough to tolerate a general anesthetic, regardless of age.
MVD following Stereotactic Radiosurgery
Some surgeons have been reluctant to perform microvascular decompression in patients who previously have undergone failed stereotactic radiosurgery because of concerns that radiation-induced scarring may increase the likelihood of damage to the trigeminal nerve during the operation and decrease the likelihood of a successful outcome after the operation. We have published a study, however, showing that although the chances of sensory complications such as numbness is higher in this group of patients, MVD can typically be completed safely and with a high cure. Therefore, our center routinely performs MVD as a “rescue” procedure for patients who are in pain despite a pervious radiosurgical procedure.