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|NI FEATURE: THE EDITORIAL DEBATE V-- PROS AND CONS
|Year : 2019 | Volume
| Issue : 2 | Page : 414-416
Trigeminal neuralgia: An orphan with many fathers
Department of Neurosurgery, Post Graduate Institute of Medical Education and Research, Chandigarh, India
|Date of Web Publication||13-May-2019|
Dr. Manjul Tripathi
Department of Neurosurgery, Post Graduate Institute of Medical Education and Research, Chandigarh
Source of Support: None, Conflict of Interest: None
|How to cite this article:|
Tripathi M. Trigeminal neuralgia: An orphan with many fathers. Neurol India 2019;67:414-6
Trigeminal neuralgia (TN) and arteriovenous malformations have many things in common. Traditionally, both diseases are considered benign; however, a study of their natural history states otherwise. For both of the diseases, the primary management was either observation with medical management or surgical management (in refractory cases). At present, radio-surgical management is considered a safe and effective treatment with robust support from the literature.,
I have read with great interest the article by Akdag et al., (The efficacy of gamma knife radiosurgery in patients with trigeminal neuralgia: The initial experience of the Bezmialem Vakif University. Neurol India 2019;67) in which they have discussed their experience with 24 patients of TN treated with gamma knife radiosurgery (GKRS). Grossly, they have reported GKRS as a safe and effective treatment modality with the development of transient and rare sensory complications in a small percentage of the patients.
At present, we have a cafeteria choice for treating TN, which ranges from medical management, percutaneous procedures (glycerol rhizotomy, radiofrequency thermal ablation, and balloon micro-compression), radiosurgical ablation (gamma knife, cyberknife, and robotic radiosurgery), peripheral neurectomy, and microvascular decompression (MVD).,,
| » What Should One Expect from the Treatment?|| |
In the present era, a patient should be well informed about the various management options, their respective indications, the expected extent and duration of pain relief, the safety and complication profile, and the cost-effectiveness of the procedure. It not only helps in realizing realistic expectations from the treatment but also avoids the chances of medico-legal litigations. The treatment starts with the correct diagnosis of the disease, and for this commentary, only typical TN (TN1) is being focused upon.
A neurosurgeon should be in a position to help the patient in choosing the option, given the best evidence available in literature [Table 1]. As rightly pointed out by the authors, GKRS takes time for achieving pain relief, and it should not be offered to patients in need of urgent pain control (e.g., patients on Ryle's tube feeding due to pain). Usually, radiosurgery comforts the patient by changing the intensity of intractable pain associated with TN to the category of tolerable pain that may be controlled with the addition of medications. Nearly one-third of patients become completely pain-free without any medication. This fact should be well emphasized to the patient beforehand. Previous studies have refuted any radio-protectant role of carbamazepine or gabapentin (the two most popular drugs given for the treatment of TN). These drugs neither affect the chances of pain relief nor reduce the incidence of complications following stereotactic radiosurgery (SRS), hence, they should be continued in the peri-procedural period.
|Table 1: Comparison of different treatment modalities for management of trigeminal neuralgia|
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The authors reported a decrease in the pain intensity in 76% of the patients, which is comparable to the published literature. The factors guiding pain control are the correct diagnosis of the disease, the prescribed dose, the target location, the duration of the disease, and the previous interventions. Pain control is also dependent on the target point. Regis et al., reported 87% pain control with 90 Gy dose targeting the Marseille point (distal-most point of the cisternal component of the trigeminal nerve close to the Meckel's cave), while Pollock et al., reported more than 90% pain control with 90 Gy prescription dose targeting the Obersteiner Redlich zone (OREZ; the boundary between the central nervous system and the peripheral nervous system, representing the transitional point along the trigeminal nerve where enveloping glial cells are replaced by Schwann cells). Messenger et al., achieved a similar pain control with 90 Gy prescription dose targeting the plexus triangular (the trilobate trigeminal ganglion; the triangular plexus is narrow, with the large motor root placed medially to the petrous part of the temporal bone) but with higher sensory complications.,,
While discussing the management option of GKRS with the patient, some issues should be focused upon: (a) Pain control would be gradual; (b) most of the patients will need some medications (though at a reduced dosage); (c) five years of pain control would be in the range of 50%-80% (Barrow Neurological Institute [BNI] grades I-III); (d) presence or absence of an offending vessel does not affect the outcome following GKRS; (e) redo GKRS can be performed in patients with an earlier good response to GKRS; (f) nearly 2%-5% of the patients do not respond to GKRS and need MVD for pain control; and (g) primary GKRS provides better pain control than secondary GKRS (that is administered following a previously performed MVD, radiofrequency ablation, rhizotomy, or radiosurgery).,,,
Owing to the non-invasive and day-care nature of GKRS, most of the patients consider GKRS as an alternative treatment for TN before embarking on MVD. The patients nonresponsive to GKRS need MVD as the next step of the management. In comparison to GKRS, MVD provides an immediate drug-free pain control for a 5-year duration in nearly 70%-80% of the patients. On the contrary, GKRS provides pain control in 70% patients at a 5-year duration, and in 30%-45.3% patients at a 10-year duration.,, For patients with predominant pain in the ophthalmic division, GKRS remains the safest treatment modality, as the complication of corneal hypoesthesia is almost never encountered.
In the reported series, the median time interval between the pain onset and the administration of GKRS treatment was 5 years (range: 1-21 years). SRS provides a better freedom from pain if performed within 3 years of pain onset (level III evidence). In the present series, it remained unclear whether all the patients suffered from typical TN, and received GKRS as a primary or secondary treatment option. The time to pain relief in different series has been reported to vary from a mean of 15-78 days and a median of 10-90 days, respectively. For all practical purposes, if the patient does not get any pain relief even after 180 days post GKRS, the treatment can be labeled as a failure.
| » Complications Following Gkrs|| |
The authors have mentioned two cases of sensory hypoesthesia in trigeminal nerve distribution (maxillary division) following GKRS. Bothersome or very bothersome hypoesthesia has been reported in 0%-17% of the patients. Sensory complications are dependent on several technical nuances: (a) The target should be at the Marseille point (distal-most point of the cisternal component of the trigeminal nerve just before its entrance into the Meckel's cave) rather than at the transition zone (OREZ), or 2-4 mm distal to the brain stem; (b) a single 4-mm shot should be used in place of two shots (to minimize the Flickinger effect, which refers to the sensory complications occurring after GKRS, following an increase in the volume of the exposed nerve to the radiation); (c) beam blocking should be avoided as far as possible; and (d) the prescription dose should not exceed 90 Gy.,
From a clinical point of view, the pain control correlates with the extent of sensory hypoesthesia and the patients reporting greater sensory deficits have better control of their pain than others. The authors have prescribed 80 Gy radiation dosage, which is a balanced dose between achieving pain control and developing sensory complications. In the cases, where radiation exposure to the brain stem exceeds the tolerable limit, the dose can be further reduced to 70 Gy or the beam-blocking technique can be used. The safe radiation dose (12-15 Gy) to the brain stem is still a matter of discussion, but every attempt should be made to minimize the radiation spillage. Targeting the Marseille point rather than a posterior target minimizes the chances of sensory complications while maintaining better pain control on a long-term (7-10 years) basis (level II evidence). Post-GKRS dry eye syndrome was only reported in a series targeting the OREZ, which is not a preferred target in the present times (level II evidence). It is important to realize that only facial numbness is the reported complication in GKRS series, while other sensory complications (decreased corneal reflex, exposure keratopathy, anesthesia dolorosa, trismus, ipsilateral masticator weakness, and dysesthesia) have been reported with cyber knife and LINAC-based series, and should not wrongly be attributed to GKRS treatment. Surprisingly, one patient in the series by Akdag et al., developed facial paresis, which remains unexplained and improved with a short course of steroids. This complication might be unrelated to the treatment and not frequently reported in the literature with GKRS techniques.
Radiosurgery induced malignancy is a very remote but possible complication, the incidence of which has been reported in 0.01%-0.001% of the patient population undergoing GKRS (a figure not different from the incidence seen in the general population). One reported complication is post-radiosurgery radiological occlusion of the superior cerebellar artery without any clinical consequence. In comparison to all the treatment options, GKRS remains the safest treatment modality of all the existing modes of treatment, which also contributes to its popularity among the patients. Though MVD is a simple procedure, it still carries a morbidity (brain-stem infarction, venous hemorrhage, ipsilateral hearing deficit, cerebrospinal fluid leak, and so on), and occasional reports of mortality.
While discussing the safety and complication profile, every neurosurgeon should mention one's own results of surgery rather than quotes from the literature, as we all do not uniformly give results similar to that obtained following MVD reported by Peter Janetta, but the results of GKRS are nearly uniform and safe (if performed in a standardized manner). Among all radiosurgical options, GKRS provides the best safety and complication profile (better than cyberknife, X knife, and robotic radiosurgery).
| » The Pain Score for Trigeminal Neuralgia|| |
The authors have used a visual analog scale (VAS) for evaluation of the pain response. The VAS is an inferior scoring system for evaluation of TN in comparison to the BNI grading scale. While evaluating the treatment response, it is also noteworthy to find the post-treatment need for medications. In the article by Akdag et al., it is not clear whether the patients were pain-free without medication or with some medication. No treatment modality provides an immediate and effective long-term medication-free pain control, as MVD does. The BNI scale evaluates the pain control and also the need for medications. It should be mandatory to use the standardized disease-specific evaluation scores to make the literature comparable; hence, the BNI pain score and the BNI sensory scoring should be used to document the severity of pain from the time of first clinical evaluation to each follow-up visit.,,
| » Cost-Effectiveness|| |
The cost-effectiveness of the procedure is an often-neglected aspect of TN treatment, which should be discussed with the patient. Although the primary expenditure incurred with the usage of the MVD is higher, it provides the best cost-effective treatment, as the patients need lesser follow-up visits, and the drug requirement is nearly curtailed. In its comparison, GKRS demands frequent patient visits (at a 6-month to an yearly interval) for providing adjustments in the drug dosages.
To summarize, GKRS is a very useful, safe, and effective treatment modality for the management of refractory typical TN. It should be considered the treatment of choice for patients in old age, those with a terminal illness, those unwilling for surgery, those with a failed MVD procedure, and those with TN secondary to small skull base lesions. It would not be wrong to say that there is no current treatment for achieving permanent cure of TN, as some risk of pain recurrence always remains, whatever be the treatment modality adopted. The pain may progress to other divisions of the TN or to the contralateral side. MVD should be considered the gold standard treatment option, but GKRS can be offered as an alternative treatment modality.,,
| » References|| |
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