Imaging studies are medically indicated for all patients presenting with trigeminal neuralgia.
the verdict
CONTESTED
contested - evenly split
refutedsupported
the weight of evidence
3 sources for · 1 against
Medical guidelines and expert reviews diverge on whether imaging is universally required, with some evidence supporting diagnostic evaluation while other sources review the limits of routine neuroimaging.
Trigeminal neuralgia (TN) is an exemplary condition of neuropathic facial pain. However, formally classifying TN as neuropathic pain based on the grading system of the International Association for the Study of Pain is complicated by the requirement of objective signs confirming an underlying lesion or disease of the somatosensory system. The latest version of the International Classification of Headache Disorders created similar difficulties by abandoning the term symptomatic TN for manifestations caused by major neurologic disease, such as tumors or multiple sclerosis. These diagnostic challenges hinder the triage of TN patients for therapy and clinical trials, and hamper the design of treatment guidelines. In response to these shortcomings, we have developed a classification of TN that aligns with the nosology of other neurologic disorders and neuropathic pain. We propose 3 diagnostic categories. Classical TN requires demonstration of morphologic changes in the trigeminal nerve root from vascular compression. Secondary TN is due to an identifiable underlying neurologic disease. TN of unknown etiology is labeled idiopathic. Diagnostic certainty is graded possible when pain paroxysms occur in the distribution of the trigeminal nerve branches. Triggered paroxysms permit the designation of clinically established TN and probable neuropathic pain. Imaging and neurophysiologic tests that establish the etiology of classical or secondary TN determine definite neuropathic pain.
Triggered paroxysms permit the designation of clinically established TN and probable neuropathic pain. Imaging and neurophysiologic tests that establish the etiology of classical or secondary TN determine definite neuropathic pain. status released display-pdf yes is-olf no is-manuscript no is-preprint no is-journal-matter no is-scanned no is-retracted no Received 2015 Dec 4; Accepted 2016 Apr 1. The diagnosis of trigeminal neuralgia (TN) critically depends on a patient's description of pathognomonic pain attacks. 1 Unequivocal definition of the characteristic features of TN is therefore mandatory.
MRI is a valuable diagnostic tool only if preceded by an evaluation of symptoms and signs that indicate probable TN. Figure 3 Neurovascular compression of the trigeminal root 3D constructive interference in steady state MRI shows axial sections at the level of trigeminal nerve root entry into the pons. (A) Bilateral neurovascular contact without morphologic changes of the root in a patient with left trigeminal neuralgia (TN). Nerve (long arrows) and blood vessel (short arrows) appear hypointense surrounded by hyperintense CSF. Contact is seen at the root entry zone as well as mid-cisternal segment.
(B, C) Morphologic changes exceeding mere neurovascular contact of the trigeminal nerve root are compatible with the diagnosis of classical TN. (B) Root atrophy in a patient with right TN. (C) Indentation and dislocation of the root in a patient with right TN (short arrow). Reliable detection of neurovascular compression requires the use of specific imaging techniques with 3D reconstruction. Several methods improve the depiction of the trigeminal nerve root and adjacent blood vessels in the posterior fossa.
However, so far too few studies have been conducted with sufficient stringency to derive diagnostic criteria with sensitivity/specificity. Most investigations involved group analyses only, and some yielded conflicting results. Pending additional evaluation, these imaging tools may in the future allow predicting the outcome of neurosurgical treatment. 44 Secondary TN. Diagnosis of secondary TN relies on the demonstration of a major neurologic disease that causes the neuralgia. A tumor at the cerebellopontine angle or MS causes TN in 15% of patients. 4 , 5 Tumors leading to TN are mostly benign and typically compress the root near its entry into the pons.
46 – 50 While MRI is the most useful investigation in the search of underlying etiology, imaging is not possible in some cases, e.g., patients with metal implants such as cardiac pacemakers. Recording of the trigeminal reflexes is an established alternative assessment of trigeminal nerve function. 51 The reflexes can be elicited from all branches of the trigeminal nerve. Reflex abnormalities achieve a sensitivity of 94% and specificity of 87% to identify secondary TN, comparable to the diagnostic accuracy of MRI. 4 , 5 Trigeminal reflex recording is particularly helpful in rare cases of TN secondary to neuropathy (appendix e-2).
Table Definition and classification of trigeminal neuralgia (TN) Even after MRI or other investigation, the etiology of TN remains unclear (idiopathic) in approximately 11% of patients. 33 – 35 Classical TN, caused by neurovascular compression, is the most frequent form of TN with defined etiology. Morphologic changes indicative of compression rather than mere vascular contact of the trigeminal root markedly increase the specificity of the diagnosis. Therapeutic relevance of these stricter criteria is supported by improved outcome of microvascular surgery in patients with clear signs of morphologic root alterations.
35 MRI is the investigation of choice to detect trigeminal nerve compression. 3D reconstructions delineate the anatomic setting with high levels of sensitivity and specificity that help avoid unnecessary posterior fossa exploration. In about 15% of patients with TN, MRI reveals a major
59 , 60 Supplementary Material Data Supplement GLOSSARY DTI diffusion tensor imaging ICHD International Classification of Headache Disorders MS multiple sclerosis TN trigeminal neuralgia Footnotes Supplemental data at Neurology.org AUTHOR CONTRIBUTIONS All authors complied with the International Committee of Medical Journal Editors criteria for authorship. This article is a review, in which all authors participated in the study concept, preliminary drafting, critical revision, and final approval. STUDY FUNDING No targeted funding reported. DISCLOSURE G.
<h4>Background</h4>Trigeminal neuralgia (TN) is a common cause of facial pain.<h4>Purpose</h4>To answer the following questions: 1) In patients with TN, how often does routine neuroimaging (CT, MRI) identify a cause? 2) Which features identify patients at increased risk for symptomatic TN (STN; i.e., a structural cause such as a tumor)? 3) Does high-resolution MRI accurately identify patients with neurovascular compression? 4) Which drugs effectively treat classic and symptomatic trigeminal neuralgia? 5) When should surgery be offered? 6) Which surgical technique gives the longest pain-free period with the fewest complications and good quality of life?<h4>Methods</h4>Systematic review of the literature by a panel of experts.<h4>Conclusions</h4>In patients with trigeminal neuralgia (TN), routine head imaging identifies structural causes in up to 15% of patients and may be considered useful (Level C). Trigeminal sensory deficits, bilateral involvement of the trigeminal nerve, and abnormal trigeminal reflexes are associated with an increased risk of symptomatic TN (STN) and should be considered useful in distinguishing STN from classic trigeminal neuralgia (Level B). There is insufficient evidence to support or refute the usefulness of MRI to identify neurovascular compression of the trigeminal nerve (Level U). Carbamazepine (Level A) or oxcarbazepine (Level B) should be offered for pain control while baclofen and lamotrigine (Level C) may be considered useful. For patients with TN refractory to medical therapy, Gasserian ganglion percutaneous techniques, gamma knife, and microvascular decompression may be considered (Level C). The role of surgery vs pharmacotherapy in the management of TN in patients with MS remains uncertain.
The trigeminal nerve is the largest of all cranial nerves. It has three branches that provide
the main sensory innervation of the anterior two-thirds of the head and face. Trigeminal neuralgia
(TN) is characterized by sudden, severe, brief, and stabbing recurrent episodes of facial pain in one
or more branches of the trigeminal nerve. Pain attacks can occur spontaneously or can be triggered
by non-noxious stimuli, such as talking, eating, washing the face, brushing teeth, shaving, a light
touch or even a cool breeze. In addition to pain attacks, a proportion of the patients also experience
persistent background pain, which along with autonomic signs and prolonged disease duration,
represent predictors of worse treatment outcomes. It is now widely accepted that the presence of
a neurovascular compression at the trigeminal root entry zone is an anatomic abnormality with a
high correlation with classical TN. However, TN may be related to other etiologies, thus presenting
different and/or additional features. Since the 1960s, the anticonvulsant carbamazepine is the drug
of choice for TN treatment. Although anti-epileptic drugs are commonly used to treat neuropathic
pain in general, the efficacy of carbamazepine has been largely limited to TN. Carbamazepine,
however, is associated with dose-limiting side-effects, particularly with prolonged usage. Thus, a
better understanding and new treatment options are urgently warranted for this rare, but excruciating
disease.
Trigeminal neuralgia-like pain that is related to an underlying disease, including tumors, trauma, viral infection, and multiple sclerosis is classified as Secondary TN. Secondary TN has a similar clinical presentation as classical TN, but may present some additional and/or different features. For instance, TN attributed to multiple sclerosis may have a bilateral presentation and TN related to tumors frequently display abnormalities in electrophysiological tests, such as trigeminal
The historical aspects of trigeminal neuropathic pain have been the subject of excellent reviews [ 8 - 10 ] and will not be addressed here. Early studies already indicated a slight female predominance in TN incidence considered nearly twice as common in women [ 3 , 5 ], a finding that has been corroborated by recent studies [ 11 - 13 ]. Additionally, a systematic review of TN prevalence found a 3:1 proportion between women and men [ 14 ]. TN is rare below the age of 40, but it can affect the pediatric population, and cases have been reported even in patients as young as 1 year of age [ 15 - 18 ].
The ophthalmic branch (V1) is afflicted less commonly, occurring in 1-5% of patients. The frequency of involvement of the V2 and V3 divisions varies in different studies, with some reporting higher incidence for the V2 and others for the V3 division [ 13 , 14 , 33 , 38 ]. The involvement of V1+V2 and V2+V3 divisions also accounts for approximately 10 and 20%, respectively, of TN cases [ 33 ], and the involvement of all three nerve branches have been reported [ 13 , 39 ].
Nerve deformity has often been observed in some studies therefore, the side of the deformed nerve correlated well with the side of TN [ 39 , 40 ]. Several alterations have been described as a result of the vascular compression, but as first proposed by Jannetta, focal demyelination at the entry zone of the trigeminal nerve seems to be one of the main mechanisms that could promote neuralgia-like pain [ 68 ]. Focal demyelination of compressed fibers was observed in TN patients and may result in the facilitation of ephaptic conduction of nerve impulses [ 63 , 69 ].
In this regard, it has been postulated that vascular compression would first impair large myelinated Aβ fibers [ 74 - 76 ]. It has also been proposed that the shock-like pain evoked by innocuous tactile stimulation represents a feature of initial stages of the disease and, as it persists, there is a progressive change in the character of pain and sensory impairment [ 74 , 76 ]. In line with this hypothesis, several clinical studies indicated that sensory abnormalities occurred more frequently in TN patients with concomitant persistent background pain [ 77 , 78 ].
The main features that differentiated TN from other forms of orofacial pain are the short duration of the pain attacks, their unilateral character, and their limitation to trigeminal nerve branches. The investigation of multiple sclerosis should always be considered in the differential diagnosis, especially in bilateral cases or in younger patients. Magnetic resonance imaging (MRI) scans can determine if there is a symptomatic cause, such as multiple sclerosis or tumors, and whether surgery is indicated. Finally, response to carbamazepine, the most effective drug in TN treatment has also been considered as a useful tool in the differential diagnostic [ 34 , 35 , 86 ].
In fact, aberrant vascular loops have been reported around the ipsilateral trigeminal nerve in patients with SUNCT as seen in patients with TN, and, as already mentioned, mild autonomic symptoms may be seen in up to 50% of patients with TN [ 44 , 88 ]. In addition, a case of TN and SUNCT coexistence has been reported in a patient afflicted by a hemorrhagic infarct of the dorsolateral medulla [ 90 ]. This observation is in agreement with early studies that pointed to a relationship between TN development and brainstem infarct [ 91 - 93 ].
Unlike carbamazepine, which is metabolized by cytochrome P450 oxidative processes, oxcarbazepine is metabolized by cytosolic enzymes, presenting a lower potential for drug interactions. Other advantages of oxcarbazepine over carbamazepine are the lack of auto-induction so that its elimination does not change significantly over time (for review [ 112 ]). Some recent comparative studies have shown similar efficacy of oxcarbazepine and carbamazepine in the treatment of TN patients, but the superiority of the safety profile of oxcarbazepine was not evident [ 54 , 113 ].
Although classical trigeminal neuralgia (CTN) is frequently caused by neurovascular contact (NVC) at the trigeminal root entry zone (REZ), both anatomical and MRI studies have shown that NVC of the trigeminal nerve frequently occurs in individuals without CTN. To assess the accuracy of MRI in distinguishing symptomatic from asymptomatic trigeminal NVC, we submitted to high-definition MRI the series of CTN patients referred to our outpatient service between June 2011 and January 2013 (n=24), and a similar number of age-matched healthy controls. Two neuroradiologists, blinded to the clinical data, evaluated whether the trigeminal nerve displayed NVC in the REZ or non-REZ, whether it was dislocated by the vessel or displayed atrophy at the contact site, and whether the offending vessel was an artery or a vein. Our data were meta-analyzed with those of all similar studies published from January 1970 to June 2013. In our sample, REZ contact, nerve dislocation and nerve atrophy were independently associated with CTN (P=.027; P=.005; P=.035 respectively). Compared to a rather low sensitivity of each of these items (alone or in combination), their specificity was high. When REZ contact and nerve atrophy coexisted, both specificity and positive predictive value rose to 100%. Meta-analysis showed that REZ NVC was detected in 76% of symptomatic and 17% of asymptomatic nerves (P<.0001), whereas anatomical changes were detected in 52% of symptomatic and 9% of asymptomatic nerves (P<.0001). In conclusion, trigeminal REZ NVC, as detected by MRI, is highly likely to be symptomatic when it is associated with anatomical nerve changes.
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