Trigeminal Neuralgia—A Comparative Analysis of Radiofrequency Electrode Lesioning Temperature at 65°C and 75°C for 60 Seconds Each

Abstract

Background

Pain affecting the distribution of one or more of the three divisions of the trigeminal nerve defines trigeminal neuralgia (TN). Radiofrequency ablation (RFA) is one of its effective treatment modalities. The ideal RFA lesioning temperature is still under evaluation.

Objective

The authors evaluate the efficacy of pain relief of RFA at 65 and 75°C, in patients with TN. Pain relief at 1 year was the study's primary outcome. Secondary outcomes: trigeminal division, complication rate, and recurrence rate.

Materials and Methods

Medical records of patients with refractory TN at our center were reviewed from January 2016 to December 2023; last new case in May 2023. Excluded were the patients who were lost to follow-up or had incomplete data. Data extracted include age, gender, lesioning temperature, and the extent of pain relief. Pain relief was recorded on a visual analogue scale of 0 to 100. Recurrence was defined as the need for repeat RFA. The data were entered and analyzed with IBM SPSS Statistics (version 26).

Results

Fifty-six patients were reviewed. The mean age was 59.6 ± 11.9 years; slight female preponderance. The commonest side of TN was the right (n = 35, 62.5%). Maxillary division (V2) was the most reported (53, 94.6%); isolated in 28 (50.0%) patients. Good-to-excellent pain relief at 1 year noted in 47 (83.9%) patients. Recurrence was 16.1%. The overall complication rate was 37.5%, commonest reported was numbness. Patients receiving the 75°C RFA had better pain relief; about 60% (n = 19) patients achieved excellent pain relief.

Conclusion

Better pain relief was observed with 75°C RFA, compared to the 65°C RFA. However, complications were higher with the 75°C RFA.

 

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Keywords

trigeminal neuralgia - radiofrequency ablation - pain relief

Introduction

Radiofrequency ablation (RFA) is a reliable minimally invasive trigeminal neuralgia (TN) treatment.[1] It offers a high initial pain relief rate, long pain-free interval after treatment, and acceptable recurrence rate.[2] [3] RFA may be indicated in patients with refractory medical treatment, inability to tolerate the side effects of medications given, at high risk of an intracranial procedure due to age or comorbid illness, and/or have had good relief of short duration on diagnostic trigeminal ganglion block.[4]

The ideal temperature range for radiofrequency (RF) electrode lesioning is still under evaluation. High temperatures may predispose to higher complications and lower temperatures may be ineffective. Several studies have utilized varied temperature levels to effect ablation of the Gasserian ganglion, quoting values from 55 to 90°C.[5]

The authors evaluate the efficacy of pain relief of RF electrode lesioning at two different RF electrode lesioning temperatures, 65 and 75°C, each for 60 second duration, in patients with TN.

 

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Materials and Methods

This retrospective study involved patients diagnosed with refractory TN who presented to our center. Ethical clearance was given by the Institutional Ethical Committee, Netaji Subash Chandra Bose Medical College, approved on 12.06.2024, number IEC/2024/5175. Informed consent was taken for photographs used in the manuscript.

All patients had undergone neurological and radiological evaluation to identify other causes of facial pain. All patients had intractable pain. The outpatient and operative records of patients who have undergone RFA for TN were retrieved from January 2016 to December 2023 with the last new patient in May 2023. Data had been prospectively collected as part of our routine clinic follow-up intervals at 14 days, 1, 3, 6, and 12 months. The author's preference is to gradually taper off medications for those who were on them preoperatively. The extent of pain relief (EPR) was recorded on a visual analogue scale from 0 to 100. The need for repeat RFA was noted as a recurrence. Phone calls were made to patients who were unable to attend their clinic visits when due. Nine patients were excluded from the study: 3 lost to follow-up and unreachable, 2 prior microvascular decompression, 2 with higher lesioning temperature, and 2 with incomplete dataset. Data such as age, gender, RF probe temperature at lesioning, need for repeat RFA, complications, and EPR at 1 year were collected.

The EPR at 1 year was the study's primary outcome. The secondary outcomes were trigeminal division involved, complication rate, and repeat RF rate.

Data were then entered into and analyzed in IBM SPSS Statistics (version 26). Categorical data were analyzed with descriptive statistics. To determine the differences between the two lesioning temperatures, the t-test and Mann–Whitney U-tests were employed. Correlations to compare the two lesioning temperatures and the EPR were done with the Spearman's rank tests. Tests of association between RF temperature with complications and repeat RF were done using the Chi-square or Fisher's exact tests, where appropriate. Statistical significance was determined at p ≤0.05.

RFA Technique

The authors conduct the procedure in the operating theater. The role of anesthesia is invaluable in the procedures' success. The procedure is detailed to the patient in the preoperative phase, ensuring a relaxed and co-operative patient through test stimulation. All patients are given antibiotic prophylaxis at induction of anesthesia.

Setup: RF generator, fluoroscopy, team with anesthetist.

Positioning

The patient is placed supine with a small sheet rolled and placed in between the scapular. The position of the head is neutral with mild extension and confirmed using fluoroscopy for absence of parallax of the anterior skull base, sella, and the clivus.

 

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Anesthesia

Standard vital monitoring is done throughout the procedure with oxygen supplementation by nasal prongs. A titration of a combination of fast-onset opioid analgesic, Fentanyl, and a short-acting anesthetic agent, Propofol, is used to keep the patient between wakeful and sedated state during the procedure. The patient is anaesthetized while negotiating the needle to the foramen ovale under fluoroscopic guidance, awakened during the test stimulation, then anaesthetized for the lesioning process. A nasopharyngeal airway may assist in the maintenance of the airway.

 

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Fluoroscopy

Lateral fluoroscopy is preferred showing a true lateral with no parallax of the anterior cranial base. The sella turcica should be sharp and clear ([Fig. 1]) as well as the clivus, petrous temporal bone, and hard palate. The posterior third of the hard palate gives the right axis to the foramen ovale.

Fig. 1 A lateral fluoroscopy view showing needle trajectory to the foramen ovale.

 

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Entry

A point from a line drawn below the lateral canthus and the angle of mouth, corresponding to about 2.5 to 3 cm lateral to the commissural labialis, is the entry point ([Fig. 2]). This point is infiltrated with 1% lidocaine.

Fig. 2 A picture showing the entry point of the insulated needle and the placement of the surgeon's index finger in the buccal mucosa.

While under the required anesthesia depth, the ipsilateral cheek and peri-oral area are cleaned with antimicrobial agent and standard sterile draping done.

 

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Trajectory

The surgeon is positioned to the patient's right. A 100 mm length, 22G insulated needle (except for the active tip which is about 5 mm) is introduced at the entry point; directed medially toward the mid-pupillary point, and medial to the mandible. The surgeon's index finger is inserted into the buccal mucosa on the lesioning side to guide the needle ([Fig. 2]). The finger palpates the mandible and the upper molars and help prevent entry into the mouth which will contaminate the needle. The guidance of the needle depends on the palpated landmarks within the mouth, surface markings, and fluoroscopy. The needle is advanced gradually on fluoroscopy, toward the posterior third of the hard palate to about 1 cm below the floor of the clivus ([Fig. 1]). The needle trajectory is usually about 45 degrees to the planum sphenoidale on a true lateral view. An oblique submental view at this stage may help guide the needle to the foramen ovale. Cerebrospinal fluid (CSF) egress may be seen upon entry of the foramen ovale. The needle engages the foramen ovale about 6 to 8 cm from the skin surface.[6]

 

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Test Stimulation

During the test stimulation, the patient is awake. The needle's stylet is removed and replaced with the RF electrode on confirming entry into foramen ovale via fluoroscopy. With the arousal of the patient, a test stimulation of 2 hertz at 0.3 to 0.5 V is given to cause muscle contraction in the division of stimulation. An increase in voltage makes the patient start moving in pain. Stimulations at 50 hertz for 1 ms pulse at 0.3 to 0.5 V leads to paresthesia in the division of the stimulation. This is communicated by the patient who has been awakened from anesthesia.

 

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RFA Dosing

The patient is sedated for the ablation when the correct placement of the electrode has been confirmed with the patient's co-operation The authors utilize a continuous lesioning dose. The RF electrode is heated up to the desired lesioning temperature of 65°C or 75°C for 60 seconds. The RF generator should report the patient's temperature accurately. Electrode impedance within the ganglion is usually 300 to 500 Ω. The impedance is helpful to confirm that the RF generator is functioning, and that the electrode is within the ganglion rather than in CSF. A curved-tip electrode may be necessary to target V1 and V2, but typically a straight electrode suffices to produce a lesion in V3.

 

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Endpoint

When lesioning is completed, the patient is awakened from anesthesia and assessed for efficacy of the procedure—the desired effect is slight hypoesthesia, such that the patient can feel touch in the affected area but cannot differentiate between the sharp and blunt ends of a safety pin.[6] The needle/electrode is then removed. The needle entry is assessed for hematoma. It may be necessary to apply pressure at the puncture site to prevent hematoma development.

 

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Postoperative Management

After the procedure, the patient is moved to the theater's recovery room for monitoring. Monitoring is done for a minimum of an hour, and the patient is discharged home on the same day. Patients on medication are gradually tapered off over the follow-up period.

 

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Results

The authors set out to ascertain the EPR, at 1 year, for patients undergoing RFA at the two RF temperatures of 65 and 75°C used at their center. Fifty-six patients were included in the study. Nine (13.8%) patients were excluded.

Patient Characteristics

The average age of patients was 59.6 ± 11.9 years. There was a slight female preponderance of 58.9% (n = 33). The differences in age and gender among the two lesioning temperatures were not statistically significant on the t-test (p = 0.873) and Mann–Whitney U-test (p = 0.534), respectively.

The commonest side of facial pain was on the right (n = 35, 62.5%). The maxillary division (V2) was the most reported (n = 53, 94.6%) TN distribution in patients, with isolated V2 in 28 (52%). All three divisions were involved in 3 (5.4%) patients. None of the patients had bilateral symptoms. Mean duration of pain, despite medications, prior to RFA was 2.7 ± 1.1 years. Forty-four (78.6%) patients needed adjunct medications ([Tables 1] and [2]).

Table 1 Patient characteristics showing gender and involved trigeminal neuralgia division

Parameter	Frequency	Percentage
Sex
Male	23	41.1
Female	33	58.9
Site of neuralgia
Right	35	62.5
Left	21	37.5
Trigeminal division involved
Ophthalmic division (V1)	13	23.2
Maxillary division (V2)	53	94.6
Mandibular division (V3)	18	32.1
Combined trigeminal divisions involved
V1	1	1.8
V1V2	9	16.1
V1V2V3	3	5.4
V2	28	50.0
V2V3	13	23.2
V3	2	3.6

Table 2 Patient outcomes following radiofrequency ablation

Parameter	Frequency	Percentage
Temperature
65°C	24	42.9
75°C	32	57.1
Need for adjunct medications
Yes	44	78.6
No	12	21.4
Extent of pain relief at 1 year
Poor relief (0–25)	9	16.1
Partial relief (26–50)	8	14.3
Good relief (51–80)	14	25.0
Excellent relief (81–100)	25	44.6
Recurrence
Yes	9	16.1
No	47	83.9
Complications
Overall complications	21	37.5
No complications	35	62.5
Numbness	16	28.6
Masseter weakness	5	8.9
Dryness of the eyes	4	7.1
Surgical-site swelling	6	10.7

 

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Radiofrequency Ablation

The 65°C group had 24 (42.9%) and 75°C group, 32 (57.1%) patients included. Good to excellent pain relief at 1 year was noted in 47 (83.9%) of patients. Nine (16.1%) had recurrence. The recurrence rate was slightly higher (16.7%) with 4 out of 24 patients in the 65°C group; the 75°C group recording 15.6% with 5 out of 32 patients. Chi-square tests on the differences in recurrence rate produced a p-value of 0.598. Two of these patients, however, opted for surgical intervention. These are detailed in [Tables 2] and [3].

Table 3 Tests of association between radiofrequency ablation (RFA) temperature with pain relief, complications, recurrence, and utilization of adjunct medication

Tests of association
Variable		Extent of pain relief at 1 year				Spearman's rank correlation coefficient	p-Value
		Poor relief (0–25)	Partial relief (26–50)	Good relief (51–80)	Excellent relief (81–100)
RFA temperature	65°C	7 (29.2%)	4 (16.7)	7 (29.2)	6 (25.0)	0.378	0.004
	75°C	2 (6.3%)	4 (12.5)	7 (21.9)	19 (59.4)
Duration of failed medical treatment with extent of pain relief at 1 year						−0.232	0.085
		Presence of complication				χ2-value	p -Value
		Yes		No		1.24	0.40[a]
RFA temperature	65°C	7 (29.2%)		17 (70.8%)
	75°C	14 (43.8%)		18 (56.3%)
		Recurrence				χ2-value	p -Value
		Yes		No		0.01	1.00[a]
RFA temperature	65°C	4 (16.7%)		20 (83.3%)
	75°C	5 (15.6%)		27 (84.4%)
		Utilization of adjunct medications				χ2-value	p -Value
		Yes		No		0.57	0.53[a]
RFA temperature	65°C	20 (83.3%)		4 (16.7%)
	75°C	24 (75.0%)		8 (25.0%)

^a Fisher's exact tests, p ≤ 0.05.

The overall complication rate among patients was 37.5% (n = 21), with 16 (76.2%) of the patients with complications reporting numbness as the commonest. Patients receiving the higher RFA temperature, 75°C, had better pain relief with about 60% (n = 19) patients achieving excellent pain relief, statistically significant (p = 0.004) on Spearman's rank tests ([Table 3]). Complications were more (43.8%) in the higher temperature group but was not statistically significant, p = 0.40 ([Table 3]). There were no mortalities.

 

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Discussion

TN is a disorder characterized by recurrent unilateral brief electric shock-like pains, abrupt in onset and termination, limited to the distribution of one or more divisions of the trigeminal nerve and triggered by innocuous stimuli.[7] The diagnosis is clinical, and patients typically report brief, lancinating attacks triggered by eating, drinking, talking, touching the face, cold, or even a puff of wind.[8] [9]

As in several studies, there was a female preponderance[10] [11] [12] with a mean age in the 6th to 7th decades[11] [12] [13] in our study. V2 is noted to be the most common division affected, with V1 least affected in most literature.[12] [14] However, there are some reported variations.[13] The right side, as in our study, has been documented[13] as the commonest side affected ([Table 1]).

Various studies used temperatures ranging from 55 to 90°C, with temperature >65°C known to destroy nerve fibers, which could further result in severe complications such as blindness, deafness, ptosis, and permanent facioplegia.[5] Our study had set out to determine the EPR in patients receiving an RFA at a temperature of 65 and 75°C. It was noted that higher ablative temperature gave better pain relief but with increased complications, as evidenced in a systematic review.[5] The better pain relief that was noted with the higher temperature of 75°C was statistically significant ([Table 3]). Further analysis in our study showed that increasing temperature increased complications but with better pain relief, and lower temperature produced fewer complications but with a reduced pain relief. These findings have been reported in several studies as well.[5] [15] [16] However, the differences noted in the complication rates with the lower temperature of 65°C and higher temperature of 75°C were not significant statistically. The better pain relief despite the higher complication rates in the 75°C group could be attributed to the fact that the commonest complication recorded, numbness, will usually present with a reduced pain sensation.

The recurrence rate, in our study, was noted to be 16.1% ([Table 2]). Although there was a slightly higher recurrence among the patients with the lower temperature, there was no statistical significance when compared to the higher temperature. This recurrence rate is higher compared to current available literature. A recent similar single-center study[15] on recurrence rate of TN treated with RFA of 80°C at 90 seconds reported a recurrence rate of 15.6%, which was almost close to that obtained in our study.

Although the findings of this study point to better pain relief with higher temperatures, more robust studies need to be done to ascertain the ideal temperature required to obtain satisfactory results with minimal complications.

 

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Limitations

The study is a retrospective one with its inherent biases. The temperature levels studied were at two levels—high and low—so, continuous scales used may not reflect the actual trends for complications and efficacy. The follow-up duration of patients was not the same; hence, aspects such as recurrence rates and their comparisons cannot be generalized. The authors propose future prospective and preferably, multicenter, randomized controlled trials to draw stronger conclusions.

 

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Conclusion

The V2 division is the commonest affected site. Patients receiving higher lesioning temperatures (75°C) obtained better pain relief despite having an increased complication rate.

 

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Conflict of Interest

None declared.

Authors' Contribution

All author contributed to conceptualization, design of work and data interpretation. T.A., M.B., C.B., H.V. contributed to data acquisition. M.B., C.B. contributed to data analysis. T.A., M.B., C.B. contributed to manuscript drafting. All authors contributed to manuscript's critical review and approval of final document and agreed to be accountable.

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Publikationsverlauf

Artikel online veröffentlicht:
25. Juni 2025