Pulsed Radiofrequency for Treating Trigeminal Neuralgia

INTRODUCTION

Trigeminal neuralgia is the most common cause of facial pain. Its estimated prevalence is 4.3 per 100,000, and the condition occurs more commonly in women than men. Trigeminal neuralgia usually affects patients >50 years but can affect younger patients, especially those with multiple sclerosis.1

The International Headache Society has specified the diagnostic criteria for trigeminal neuralgia.2,3 Diagnosis is confirmed if the patient has had at least 3 attacks of unilateral facial pain with the following characteristics:

• Meeting at least 1 of the following 4 criteria: (1) paroxysmal and lasting from a fraction of a second to 2 minutes; (2) severe; (3) electric shock–like, shooting, stabbing, or sharp; (4) precipitated by nonpainful stimuli

• Occurring in at least 1 division of the trigeminal nerve with no radiation beyond its distribution

• Lacking neurologic deficits and any other identifiable causes

Treatment of trigeminal neuralgia is challenging. Medical options include carbamazepine and oxcarbazepine as primary agents, although practitioners prescribe other neuropathic agents such as neuroleptics and anticonvulsants with variable degrees of success.4 Carbamazepine has been used since 1960 for its efficacy in approximately 60%-80% of patients; however, its side effects and possible loss of efficacy have encouraged the search for other drugs.5 Only an estimated 25% of patients will achieve total long-term pain control using medications,4 indicating that the majority of patients will require an intervention at some point to treat their pain.

Surgical options include neurovascular decompression, balloon compression, glycerol gangliolysis, and radiofrequency ablation (RFA).6 Surgeries, although reported to be successful, can have significant risks and complications.

The goal of vascular decompression is trigeminal nerve decompression from compressing vessels. Trigeminal nerve decompression was successful for 1-2 years with a decline in efficacy after 10 years.7 In addition, this surgical procedure has the risk of complications.

Balloon compression is performed under general anesthesia. A Fogarty balloon is inserted into the Meckel cave and inflated with a dye. The appropriate duration for compression remains controversial.8 This procedure provides short-term pain relief, but long-term relief is variable. Balloon compression includes risks associated with the procedure, as well as the additional complications of general anesthesia.9

Glycerol gangliolysis requires an injection of glycerol through the foramen ovale. Although the procedure is initially successful in relieving pain, efficacy at 12 months is variable, and recurrence rates at 12 months can reach 53%.10 An important problem with this procedure is the spread of glycerol beyond the ganglion and the lack of selectivity that can cause damage to motor and autonomic fibers.

The role of RFA in treating trigeminal neuralgia has been described but has not been well studied. The traditional technique is to place the RFA needle through the mouth until it is in proximity to the foramen ovale (close to the gasserian ganglion) and then to perform RFA, but this technique is associated with pain and soft tissue trauma.11

Several other procedures have been described for treating trigeminal neuralgia: stereotactic radiosurgery, alcohol injection, cryotherapy, local light amplification by stimulated emission of radiation, and electroacupuncture.12 None of these procedures provides long-term efficacy, some require general anesthesia, and they all have complications. Complications may be surgical or result from the lack of selectivity that damages nerve fibers, ultimately leading to the loss of motor and autonomic functions.

We present a case series in which patients with trigeminal neuralgia resistant to conservative therapy that included antidepressants, anticonvulsants, and opioids (for some patients) were effectively treated with pulsed radiofrequency (PRF)—applying energy intermittently rather than continuously as in RFA—using a transcoronoid approach rather than the traditional approach through the mouth.

RESULTS

Our study included 8 patients, 6 females and 2 males, with an average age of 56.4 ± 13 years (Table 1). One patient reported the development of the trigeminal neuralgia after getting herpes zoster, 3 patients after a motor vehicle accident, and 1 patient after left posterior fossa decompression. The remaining patients did not report a triggering event.

One patient reported improvement in the distribution of V1 and V2 branches but no improvement in the distribution of V3 branch, so we excluded this patient from the comparison of preprocedure and postprocedure pain scores. Seven patients reported a statistically significant decrease in their pain scores. All patients also reported improvement of their neuralgia episodes (Table 2).

Duration of improvement ranged from 91-462 days at the time of follow-up, and 3 patients reported ongoing relief at 60, 70, and 85 days after the follow-up period. None of the patients reported any complications after the procedure.

DISCUSSION

Our case series presents a novel method of performing PRF for patients with trigeminal neuralgia that is resistant to medical management. The procedure results in excellent pain relief, and the lack of side effects reported in our series suggests that PRF is also a safe procedure.

RFA and PRF have previously been described as modalities for treating trigeminal neuralgia by using an approach through the mouth. RFA, while effective, may cause nonselective damage to the nerve that can lead to the loss of motor and autonomic function. In a large study that included 1,600 patients who received RFA for treating trigeminal neuralgia, the authors reported the following complications: diminished corneal reflex, masseter weakness and paralysis, dysesthesia, anesthesia dolorosa, keratitis, transient paralysis of cranial nerves III and VI, cerebrospinal fluid leakage, carotid-cavernous fistula, and aseptic meningitis.13

PRF does not produce thermal lesions, but evidence suggests that microscopic damage to axonal microfilaments and microtubules can occur, with greater changes seen in C fibers than A-beta or A-delta fibers, the fibers principally responsible for pain transmission.14 Studies of PRF used to treat trigeminal neuralgia have been variable. Erdine et al compared RFA vs PRF and found that PRF was not effective in treating trigeminal neuralgia,15 while another series showed that long-term efficacy was obtained.16 However, these studies used the classic approach to target the gasserian ganglion through the foramen ovale.

Our study suggests the efficacy of PRF treatment for trigeminal neuralgia. This efficacy might be attributed to the different technique we used to target the branches as they exit the gasserian ganglion rather than targeting the ganglion itself. Our patients did not report any side effects or complications with our approach, suggesting the safety of the transcoronoid approach.

Limitations of our study are that our case series involved a limited number of patients, and we lacked a control group. In addition, the analysis was retrospective, and the outcomes were pain scores and percent improvement; our records did not contain data on functional improvement. Although retrospective data collection has limitations, the percent improvement after procedure and the pain scores were well reported in our electronic medical record. Further, all cases were performed by one provider, eliminating any interperformer variability.

CONCLUSION

Our study suggests that PRF through the transcoronoid approach may be a safe and effective approach for treating trigeminal neuralgia in patients resistant to conservative management.