Classification of trigeminal neuralgia: clinical, therapeutic, and prognostic implications in a series of 144 patients undergoing microvascular decompression

Clinical article

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Object

Trigeminal neuralgia (TN) presents a diagnostic challenge because of the variety of symptoms, findings during microvascular decompression (MVD), and postsurgical outcomes observed among patients who suffer from this disorder. Recently, a new paradigm for classification of TN was proposed, based on the quality of pain. This study represents the first clinical analysis of this paradigm.

Methods

The authors analyzed 144 consecutive cases involving patients who underwent MVD for TN. Preoperative symptoms were classified into 1 of 2 categories based on the preponderance of shocklike (Type 1 TN) or constant (Type 2 TN) pain. Analysis of clinical characteristics, neurovascular pathology, and postoperative outcome was performed.

Results

Compared with Type 2 TN, Type 1 TN patients were older, were more likely to have right-sided symptoms, and reported a shorter duration of symptoms prior to evaluation. Previous treatment by percutaneous or radiosurgical procedures was not a predictor of symptoms, surgical findings, or outcome (p = 0.48). Type 1 TN was significantly more likely to be associated with arterial compression. Venous or no compression was more common among Type 2 TN patients (p < 0.01). Type 1 TN patients were also more likely to be pain-free immediately after surgery, and less likely to have a recurrence of pain within 2 years (p < 0.05). Although a subset of patients progressed from Type 1 to Type 2 TN over time, their pathological and prognostic profiles nevertheless resembled those of Type 1 TN.

Conclusions

Type 1 and Type 2 TN represent distinct clinical, pathological, and prognostic entities. Classification of patients according to this paradigm should be helpful to determine how best to treat patients with this disorder.

Abbreviations used in this paper: GKS = Gamma Knife surgery; MVD = microvascular decompression; TN = trigeminal neuralgia.

Trigeminal neuralgia is defined as a syndrome of severe, paroxysmal bursts of pain in one or more branches of the trigeminal nerve. The pathophysiology is believed to be related to compression of the trigeminal nerve by a blood vessel at or near the root entry zone.8,10,11,13 Ectopic action potential generation in the sensory root may be responsible for the generation of pain,3,6 and central and peripheral demyelination also occur as a result of nerve root injury.9,12 After MVD of the trigeminal nerve, nerve conduction improves14 and pain is alleviated in the vast majority of patients,1,16 supporting the hypothesis that vascular compression is a major causative or contributive factor in many patients who suffer from TN.

There is substantial evidence that TN is not a homogeneous disorder. Patients report a wide spectrum of symptoms, from the classic episodic electric lancinating pain to a more constant aching, throbbing, or burning pain.4,17 At surgery, arterial or venous compression of the nerve is often observed, but occasionally there is no vascular compression despite entirely classic symptoms. Some patients improve immediately and dramatically after MVD, whereas others continue to experience some degree of pain, and some have recurrence of their pain after an initial good result. It is therefore likely that TN is multifactorial and does not represent a single, discrete disease, and each subtype has its own natural history and optimal treatment.

Previous discussions of TN have discriminated “typical” from “atypical” forms, with “atypical” variously defined as departing in some way from the classic description. We have previously proposed a classification scheme that clearly defines 2 subtypes of TN based on the preponderance of shocklike or constant pain.4,7 Patients who describe > 50% of their pain as sharp, lancinating, and shocklike with pain-free intervals are classified as having Type 1 TN, and those with > 50% constant symptoms (aching, throbbing, or burning) are classified as having Type 2 TN. The advantage of this system is that there is an unambiguous and easily assessed criterion that objectively differentiates the 2 groups of patients.

The patient's history is the most powerful means of establishing a diagnosis of TN, so this paradigm already represents an effectively standardized means of communication about the disorder. If the 2 clinical subtypes of TN also have different surgical findings and long-term outcomes, the classification should be helpful for making decisions about optimal therapy as well. In this study, we demonstrate that these 2 groups do in fact represent distinct clinical, pathological, and prognostic entities.

Methods

We identified 157 consecutive patients undergoing MVD for TN over a 5-year period from January 2001 to December 2005 at our institution. Thirteen patients had a history of multiple sclerosis and were excluded from the study. The 144 remaining patient's symptoms were classified as Type 1 or Type 2 TN by the senior author (K.J.B.) at the time of initial clinical evaluation. All patients underwent retromastoid craniectomy and MVD of the trigeminal nerve performed by the senior author (K.J.B.). The retrospective review involved analysis of charted information from pre- and postoperative clinical notes, operative reports, and other clinical information available from the hospital mainframe computer system and clinical charting system. Statistical analyses were performed using Statistical Package for the Social Sciences version 15 for Windows (SPSS, Inc.). The Student t-test was used for parametric data, and the Mann-Whitney U-test was used for nonparametric data, with a probability value of 0.05 using a 2-tailed test considered statistically significant. Chi-square was used for all categorical data. The study was approved by the Oregon Health & Science University Institutional Review Board.

Results

Among the patients studied, 104 (72%) presented with complaint of Type 1 TN symptoms at onset and 40 (28%) with Type 2 TN symptoms. Differences in baseline characteristics between patients with Type 1 and Type 2 TN are shown in Table 1. Patients with Type 1 TN tended to be significantly older (57 vs 50 years of age), were more likely to have right-sided symptoms (70 right-sided vs 17 left-sided), and reported shorter median duration of symptoms prior to evaluation (48 vs 60 months). By contrast, in patients with Type 2 TN, there was no side predilection (p = 0.34). The percentage of patients who were women was higher in the Type 2 TN group, but the difference did not achieve statistical significance (p = 0.09). The likelihood of having had a previous destructive procedure to the trigeminal nerve, such as percutaneous rhizolysis or GKS, was comparable in the 2 groups, as was the likelihood of having some preoperative response to antiepileptic medication.

TABLE 1:

Baseline characteristics of patients with Type 1 and Type 2 TN*

CharacteristicType 1 TNType 2 TNp Value
no. of patients10440
mean age in yrs57500.0007
median duration in mos48600.04
female73 (70)33 (83)0.09
right-sided TN70 (67)17 (45)0.006
previous lesion16 (15)6 (15)0.95
response to medication62 (60)21 (53)0.44

* Values represent numbers of patients (%) unless otherwise indicated.

Findings at surgery are represented graphically in Fig. 1. Patients with Type 1 TN symptoms were almost twice as likely as those with Type 2 TN to have arterial compression and were much less likely to have only venous compression observed. Conversely, among patients with Type 2 TN symptoms, venous compression was seen nearly as often as arterial compression, and these patients were 5 times more likely than those with Type 1 TN to have no compressive vessel observed at surgery (p < 0.05). Altogether, 6 patients were found to have no evidence of neurovascular contact; in each of these, the nerve was gently stretched intraoperatively to produce a lesion.

Fig. 1.
Fig. 1.

Bar graph illustrating the surgical findings of artery and vein compression findings in patients with Type 1 and Type 2 TN.

Surgical findings and outcome after surgery are shown in Table 2. Patients with Type 1 TN symptoms were much more likely to have initial pain relief and less likely to have recurrence of pain requiring an additional procedure within 2 years (p < 0.05). Twenty-two patients had previously undergone a destructive procedure (percutaneous rhizolysis or GKS) and had a recurrence of TN. As shown in Table 3, history of such a procedure did not predict surgical findings or outcome.

TABLE 2:

Surgical findings and postsurgical outcome by TN type*

FindingType 1 TNType 2 TNp Value
arterial compression82 (79)19 (48)0.0002
venous compression only20 (19)17 (43)0.004
no compression2 (2)4 (10)0.03
pain-free postop99 (95)33 (83)0.01
recurrence w/in 2 yrs14 (13)11 (28)0.04

* Values represent numbers of patients (%) unless otherwise indicated.

TABLE 3:

Surgical findings and postsurgical outcome by history of destructive procedure*

Finding or OutcomeLesionNo Lesionp Value
no. of patients22122
Type 2 TN6 (27)34 (28)0.95
arterial compression17 (77)84 (69)0.42
venous compression only4 (18)33 (27)0.38
no compression1 (5)5 (4)0.92
pain-free postop21 (95)111 (91)0.48
recurrence w/in 2 yrs5 (23)20 (16)0.47

* Values represent numbers of patients (%) unless otherwise indicated.

We identified a group of 6 patients who presented initially with Type 1 TN symptoms but subsequently progressed to Type 2 TN over time. Characteristics of this group are shown in Table 4. These patients tended to have significantly longer preoperative duration of symptoms than the other patients (median 84 months). However, their characteristics were otherwise similar to those of patients with Type 1 TN, since arterial compression was more likely to be observed at surgery, and they were generally pain-free immediately after MVD without shortterm recurrence.

TABLE 4:

Characteristics of cases patients progressing from Type 1 TN to Type 2 TN*

VariableValue
no. of patients6
female4
right-sided TN4
previous lesion1
mean age in yrs57
median duration in mos84 mos
arterial compression5 (83)
pain-free postop6 (100)
recurrence w/in 2 yrs0 (0)

* Values represent numbers of patients (%) unless otherwise indicated.

Discussion

Diagnosis of TN is fairly straightforward, but until recently there has been no clear systematic paradigm for classification of patients with this condition. It has been postulated that TN is a heterogeneous clinical condition, with “typical” symptoms associated with more severe arterial compression15 and better clinical outcome,17 and “atypical” symptoms more likely to involve some other pathological process.2 In this study, we demonstrated that the recently proposed classification scheme of Type 1 and Type 2 TN based on predominance of episodic or constant pain4 does distinguish significantly different populations of patients with distinct clinical characteristics, neurovascular pathology found at surgery, and postoperative prognosis.

We found that patients with a history of a destructive procedure such as GKS or percutaneous rhizolysis by means of radiofrequency electrode, balloon compression, or glycerol did not predict different symptoms, surgical findings, or outcome after MVD. It is important to note that these patients represent recurrence of TN pain after an initially successful destructive procedure. Patients who develop new pain after a destructive procedure are classified as having trigeminal deafferentation pain, and these patients are very different from those with either Type 1 or Type 2 TN.4

The finding that a few patients with very long–duration Type 1 TN symptoms that eventually evolve to predominantly Type 2 TN symptoms has implications for treatment and prognosis. Although the numbers are too small to be statistically significant, these patients tended to have pathological and prognostic characteristics similar to those of the patients with Type 1 TN, suggesting that the TN type at onset is more meaningful than type of pain at evaluation. This phenomenon may also provide some insight into the natural history of TN. In these patients, TN seems to be a progressive disease, suggesting that patients with Type 1 TN may eventually progress into Type 2 TN if no intervention is performed. We also found many patients who suffered with Type 1 TN symptoms for many years and never developed Type 2 TN pain. However, if Type 2 TN progression represents deterioration of Type 1 TN, these may in fact be sequential stages of the same disease process, with Type 2 TN representing the clinical sequela of more advanced trigeminal neuropathy.5 Further clinical studies will be required to prove or disprove this theory.

Our data suggest that patients with Type 2 TN represent a somewhat more heterogeneous population than those with Type 1 TN, since they are less likely to have right-sided pain, arterial compression, and an excellent clinical outcome. It is worth noting, however, that arterial compression was still the most common finding among patients with Type 2 TN, and a majority of patients with Type 2 TN symptoms had a good postoperative outcome. Therefore, presence of Type 2 TN symptoms must not be considered a contraindication to MVD, but the surgeon and the patient must be aware that the likelihood of a good result is somewhat less than with classic Type 1 TN pain. Ultimately, the decision to proceed with surgery involves a thorough analysis of the patient's clinical presentation, including response to medications, trigger points, painfree intervals, and memorable onset of pain, all of which may be present with either type of TN.

Conclusions

Type 1 and Type 2 TN represent distinct clinical, pathological, and prognostic entities. Classification of patients according to this paradigm should be helpful to determine how best to treat patients with this disorder.

Disclaimer

The authors report no conflict of interest concerning the materials or methods used in this study or the findings specified in this paper.

Acknowledgments

The authors would like to express their appreciation and thanks to Shirley McCartney, Ph.D., for editorial assistance, and Valerie Anderson, Ph.D., for electronic institutional review board assistance.

References

Article Information

Address correspondence to: Kim J. Burchiel, M.D., Department of Neurological Surgery, Mail Code: CH8N, Oregon Health & Science University, 3303 SW Bond Avenue, Portland, Oregon 97239. email: burchiek@ohsu.edu.

Please include this information when citing this paper: published online April 24, 2009; DOI: 10.3171/2008.6.17604.

© AANS, except where prohibited by US copyright law."

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Figures

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    Bar graph illustrating the surgical findings of artery and vein compression findings in patients with Type 1 and Type 2 TN.

References

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