Trigeminal Neuralgia
Ronald Brisman, M.D.

Typical versus Atypical Trigeminal Neuralgia Perspective Statement

Brisman R: Typical versus Atypical Trigeminal Neuralgia and Other Factors that may Affect Results of Neurosurgical Treatment. World Neurosurgery February 22, 2012 [Epub ahead of print]. PMID: 22366746. http://dx.doi.org/10.1016/j.wneu.2012.02.047  

The following is a revised personal version of the text of the final journal article.

In WORLD NEUROSURGERY (2012), Zhang et al
http://dx.doi.org/10.1016/j.wneu.2012.01.040 review their results of treating 154 consecutive patients with trigeminal neuralgia (without a defined cause such as brain tumor or multiple sclerosis) with pure microvascular decompression (MVD) (7). Factors associated with complete pain relief without medicines after five years were: typical symptoms, preoperative magnetic resonance imaging (MRI) indicating vessel compression, and obvious vessel compression found at operation, which were present respectively in 64, 64, and 53 percent of patients. Initial and 5 year complete pain relief were seen respectively in 87 and 80 percent of those with typical trigeminal neuralgia and 79 and 54 percent of those with atypical trigeminal neuralgia. There were no major complications.

A prior ablative procedure did not influence the outcome following MVD and was done in 56 (39%) of patients: 39 (25%) peripheral nerve procedures, 26 (17%) radiofrequency thermorhizotomy, 23 (15%) gamma knife radiosurgery, 14 (9%) percutaneous glycerol rhizotomy.

Other neurosurgical procedures for trigeminal neuralgia, such as Gamma Knife radiosurgery (GKRS) and needle rhizotomy (radiofrequency, glycerol and balloon microcompression) have also been shown to be more effective for typical than atypical trigeminal neuralgia. It is therefore particularly important for neurosurgeons to recognize the difference between these two entities.

In addition to paroxysmal, triggered, trigeminally distributed pain, atypical trigeminal neuralgia usually has constant or persistent pain, which is often aching, nagging, burning, or throbbing. However, it is not unusual for patients with typical trigeminal neuralgia to have throbbing, burning, nagging, or aching pains in addition to the shooting, stabbing and sharp pains that are characteristic of typical trigeminal neuralgia. So how can one distinguish between atypical and typical trigeminal neuralgia, both of which can be associated with constant pain?

The constant pain that is consistent with typical trigeminal neuralgia has several features. Pain is often triggered by talking or moving the tongue and is relieved when the patient holds completely still even for a few minutes. It often develops in a patient who used to have typical paroxysmal, triggered pain without constant pain, who later develops constant pain in addition to typical paroxysmal, triggered pain. It is present during a flare up of paroxysmal, triggered pain but then subsides when the paroxysmal, triggered pain subsides. This constant pain is often exquisitely sensitive to carbamazepine or oxcarbazepine and responds very well, as does its accompanying paroxysmal pain, to neurosurgical interventions, similar to cases of typical trigeminal neuralgia without this kind of constant pain.

The constant pain that is characteristic of atypical trigeminal neuralgia is similar to the constant pain seen in persistent idiopathic facial pain (formerly called atypical facial pain). This pain is not triggered by talking, eating, or moving the mouth or tongue and is not relieved when the patient holds completely still; it is often made worse by such a maneuver. It was never absent during a period of paroxysmal triggered pain. It is present even when there is no paroxysmal, triggered pain. It does not respond to carbamazepine or oxcarbazepine and is less likely to respond to neurosurgical interventions. When such nontriggered constant pain exists in the absence of any paroxysmal triggered pain (chronic idiopathic face pain), it is unlikely to respond to neurosurgical intervention.

By failing to clearly distinguish between different kinds of constant pain and regarding the presence of any kind of constant pain, when associated with some paroxysmal triggered pain, as enough to diagnose atypical trigeminal neuralgia, some studies show that patients with atypical trigeminal neuralgia do worse than those with typical trigeminal neuralgia following MVD, as in the present study (7). However, other studies show that patients with atypical trigeminal neuralgia (6) or constant pain (5) do just as well as those with typical symptoms.

Confusing the issue of atypical trigeminal neuralgia further is the use of TN2, which some erroneously equate with atypical trigeminal neuralgia. TN2 is diagnosed when patients with face pain of spontaneous onset have constant pain that they report as being present more than 50 percent of the time (4). However, patients with TN2 respond to MVD depending on whether they have the constant pain of typical trigeminal neuralgia, atypical trigeminal neuralgia, or persistent idiopathic facial pain (where there is no paroxysmal triggered pain): very well (typical trigeminal neuralgia), not so well (atypical trigeminal neuralgia), or not at all (persistent idiopathic facial pain). The most reliable way to diagnose atypical trigeminal neuralgia is to have the diagnosis made by an experienced clinician (attuned to the different kinds of face pain including constant pain), rather than relying on a percentage of time that the patient feels constant pain is present.

Other characteristics have been shown elsewhere to be associated with a smaller chance of long-term pain relief following MVD include female gender, venous compression of the trigeminal-root entry zone; a duration of preoperative symptoms of =>eight years, and lack of immediate postoperative relief (1). Similar to the results published in the current issue of WORLD NEUROSURGERY (7), others have also shown that a history of ablative procedure before MVD did not significantly increase the likelihood of recurrent tic pain (1).

Although some have argued that MVD should be done early because patients who have trigeminal neuralgia for a long time do less well than those with a shorter history, the present study, which shows no unfavorable outcome with a longer history, casts doubt on this reasoning. Similarly, the argument that MVD should be done first because other ablative procedures worsen the outcome following MVD is also called into doubt by the present and other studies (1).

Preoperative MRI can be helpful in further selecting patients who are more likely to benefit from MVD. MRI evidence of vessel compression, which was seen in only 64 percent of patients, was more likely to be associated with a better prognosis for long term pain relief (7). This percentage probably includes those with a large tortuous vertebrobasilar artery, which is not a situation that is readily amenable to pure MVD because it is not easy to mobilize such a vessel away from the trigeminal nerve. In addition, this percentage probably includes those with venous compression of the trigeminal nerve—another situation where pure MVD is less likely to work (1). MRI showing blood vessel contact with the trigeminal nerve may also indicate a particularly favorable response to GKRS (2).

Pure MVD without denervation is not always possible or desirable, as in the following situations: a vessel, usually a vein, runs right through the trigeminal nerve; the compressing artery is very large and arteriosclerotic; the artery (usually superior cerebellar) is very impacted into the trigeminal nerve; there is no vascular compression; or only a vein is in contact with the trigeminal nerve. Because denervating procedures such as GKRS and needle rhizotomy also have a very good chance of providing pain relief and do not have an impact on results of a subsequent MVD, these minimally invasive procedures prior to or instead of an MVD are very attractive alternatives.

Although MVD probably has the best chance of long-lasting pain relief without bothersome numbness (3), it is a major procedure and is associated with many complications. Zhang et al. have properly emphasized the need for a complete and frank discussion with the patient before surgery regarding risks, benefits, and alternatives (7).

REFERENCES:
  1. Barker FG, Jannetta PJ, Bissonette DJ, Larkins MV, Jho HD: The long-term outcome of microvascular decompression for trigeminal neuralgia. NEJM, 334:1077-1083, 1996.
  2. Brisman R, Khandji G, Mooij RBM: Trigeminal nerve-blood vessel relationship as revealed by high-resolution magnetic resonance imaging and its effect on pain relief after gamma knife radiosurgery for trigeminal neuralgia. Neurosurgery, 50:1261-1266, 2002.
  3. Brisman R: Microvascular decompression vs. gamma knife radiosurgery for typical trigeminal neuralgia: preliminary findings. Stereotactic and Functional Neurosurgery, 85:94-98, 2007.
  4. Burchiel KJ: A new classification for facial pain. Neurosurgery, 53:1164-1167, 2003.
  5. Sandell T, Eide PK: Effect of microvascular decompression in trigeminal neuralgia patients with or without constant pain. Neurosurgery, 63:93-99, 2008.
  6. Sindou M, Leston J, Howeidy T, Decullier E, Chapuis F: Micro-vascular decompression for primary trigeminal neuralgia (typical or atypical). Long-term effectiveness on pain; prospective study with survival analysis in a consecutive series of 362 patients. Acta Neurochir (Wien), 148:1235-1245, 2006.
  7. Zhang H, Lei D, You C, Mao BY, Wu B, Fang Y: The long-term outcome predictors of pure microvascular decompression for primary trigeminal neuralgia. World Neurosurgery (2012). DOI: 10.1016/j.wneu.2012.01.040
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