How aggressive should neurologists be about ordering diagnostic tests for patients with trigeminal neuralgia (TN), the cause of recurrent, sporadic, sudden burning or shock-like pain in the face? Which tests should they order? What does the evidence suggest about the best course of treatment? The AAN Quality Standards Subcommittee addressed these issues in a review of the best available evidence, and the findings were published ahead of print on Aug. 20 on www.Neurology.org.
Lead author Gary Gronseth, MD, professor and vice chair of neurology at the University of Kansas, discussed the new AAN practice parameters on diagnosis and treatment of TN in a telephone interview with Neurology Today.
HOW DOES HAVING GUIDELINES HELP DOCTORS DIAGNOSE AND TREAT PATIENTS WITH TRIGEMINAL NEURALGIA?
The guideline summarizes and synthesizes many studies pertaining to the diagnosis and treatment of trigeminal neuralgia. It would be difficult for a practicing neurologist to sift through this vast literature alone. Doctors can then approach the diagnosis and treatment of their patients with confidence that they understand the state of the evidence to inform their diagnostic and treatment decisions.
WHAT IS THE CHALLENGE IN DIAGNOSING PATIENTS WITH TN? HOW DOES IT USUALLY PRESENT?
Usually the diagnosis of TN is straightforward. It is made based on the patient's history of brief, paroxysmal severe unilateral facial pain often triggered by touching the face or chewing.
After establishing that the patient has TN, the next step is to attempt to determine the cause. Although most patients have classic TN, in which the cause is not determined, a few will have symptomatic TN where the symptoms are related to a tumor compressing the nerve or even a multiple sclerosis plaque. The neurologist needs to exercise judgment in deciding how aggressive to be in ordering diagnostics tests to identify the few patients with symptomatic TN.
WHAT WOULD BE AN AGGRESSIVE APPROACH?
An aggressive approach would include an MRI and TN reflex testing. Doctors could also do a lumbar puncture because a few patients have TN as a result of chronic meningitis, particularly those who are systemically ill, have fevers, documented Lyme disease, or known cancer, which can sometimes spread to the CNS. You treat the pain the same way, but then you also treat the underlying cause.
THE QSS REVIEWED THE LITERATURE ON PRACTICE, PHARMACOLOGICAL, AND SURGICAL APPROACHES TO TN. WHAT WAS THE HARDEST ASPECT TO CREATE GUIDELINES FOR, AND WHY?
The surgical literature was the hardest to assess. Many surgical studies were identified, but most of them were retrospective analyses of case series with a high risk of bias. Sifting through these studies to find those with the lowest risk of bias was a challenge.
THE PARAMETER NOTES THAT IT'S STILL UNCERTAIN WHETHER OR NOT MRI IS USEFUL IN DIAGNOSING TN. WHY?
The best available evidence indicates that up to 15 percent of patients with TN will have symptomatic TN — meaning that MRI would find an underlying structural cause of the neuralgia. Fifteen percent would be a high yield of MRI. Most clinicians would judge it worth the expense of routinely performing MRI on TN patients with that high a figure.
However, the studies that considered the value of MRI were done at referral centers with a special interest in TN. TN patients referred to specialized centers are probably not typical of TN patients seen in a general neurologist office. Hence, the yield of MRI in non-referred TN patients is probably considerably less than the 15 percent reported. Uncertainty remains. Given the limitations of this evidence, a reasonable neurologist might judge it unnecessary to send TN patients routinely for MRI.
Clinical clues that they may have symptomatic TN include bilateral TN or if numbness is mentioned in the history and sensory loss is found on neurological examination of the face.
SO DO YOU THEN ORDER AN MRI? WHEN?
Because of the limitations of the evidence, the decision to obtain an MRI comes down to the judgment of the individual physician. The only clinical features that identify patients at an increased risk of having symptomatic TN are trigeminal sensory deficits and bilateral involvement. Unfortunately, few patients with symptomatic TN have these features so the absence of facial numbness or bilateral involvement does not “rule out” a structural cause of TN.
THE QSS FOUND THAT DRUG THERAPY WAS USEFUL, PARTICULARLY CARBAMAZEPINE AND OXCARBAZEPINE. BUT CARBAMAZEPINE SEEMED TO HAVE MORE ADVERSE EVENTS. WHAT KINDS OF PATIENTS HAVE PROBLEMS TOLERATING CARBAMAZEPINE?
Any patient can get side effects from either medication but, older patients, particularly those on multiple medications, are the most sensitive to side effects of carbamazepine.
IT IS UNCLEAR WHEN DOCTORS SHOULD TALK TO PATIENTS ABOUT SURGERY. WHAT DOES THE EVIDENCE SUGGEST?
It is unclear from the evidence when surgery should be discussed. What is clear is that there is no strong evidence for the efficacy of any medication beyond carbamazepine and oxcarbazepine. Indeed, the strength of the evidence for the effectiveness of surgery is similar to that of the medications with weaker evidence of effectiveness.
Most often physicians will try numerous medications with weak evidence of effectiveness before considering surgical options. Given the state of the evidence, it would be equally reasonable to consider surgery earlier before attempting these alternative medications. The optimal point at which trials of medical management should be abandoned in favor of a surgical option is unclear. It again comes down to the judgment of physician and patient.
MICROVASCULAR DECOMPRESSION (MVD) SEEMED TO BE THE MOST SUCCESSFUL SURGERY, BUT IT IS MORE INVASIVE THAN GAMMA KNIFE THERAPY AND HAS MORE SERIOUS COMPLICATIONS. WHEN WOULD YOU RECOMMEND ONE OVER THE OTHER?
Given the absence of high quality studies directly comparing one procedure to another it is difficult to determine the relative merits. Both MVD and ablative procedures directed at the trigeminal nerve root seem to be more effective and have more prolonged duration of pain relief than procedures directed at the peripheral portion of the trigeminal nerve. Between MVD and the gamma knife it is a close call. I think it is a trade-off between the more rapid relief of MVD (usually immediately after surgery) than after gamma knife treatment but with the risk of the craniotomy that goes with MVD.
HOW CAN NEUROLOGISTS TRANSLATE THESE PARAMETERS INTO PRACTICE?
There are two major points. First, there are few drugs with strong evidence of effectiveness in treating TN. If patients fail to respond to these drugs, physicians should not be reluctant to consider referring the patient for surgery. Often, surgery is considered a last resort and patients suffer while the well-intentioned physician tries still other medications with limited effectiveness.
Second, it is reasonable to consider the routine use of cranial MRI on all patients with TN to identify those with the symptomatic form.
Gronseth G, Cruccu G, Zakrzewska JM, et al. Practice Parameter: The diagnostic evaluation and treatment of trigeminal neuralgia (an evidence-based review): Report of the Quality Standards Subcommittee of the American Academy of Neurology. Neurology 2008; E-pub 2008 Aug. 20.