Introduction

Trigeminal neuralgia (TN) is the most common cause of neuropathic facial pain, with an annual incidence of 3–5 new cases per 100,000 population [1]. Idiopathic TN is classified to typical and atypical forms based on the clinical manifestations. Atypical cases usually have continuous pain between the classic paroxysmal lancinating attacks [2]. Atypical TN cases are usually less responsive to conventional medical treatments like carbamazepine or oxcarbazepine and the standard microvascular decompression surgeries [3]. This increases the social, psychological, and occupational burden of the disease.

There are different treatment modalities in cases with refractory TN including microvascular decompression, Gamma Knife surgeries, and radiofrequency (RF) procedures [4,5,6]. RF is less invasive and safe, with immediate results and minimal side effects apart from facial numbness, which is usually accepted by the patients [7].

Patients with typical TN usually respond to RF ablation [7,8,9,10,11,12,13]. Yet, limited studies have addressed the efficacy of RF in cases with atypical trigeminal neuralgia [14, 15]. The aim of this study is to examine the effects of RF ablation in cases with atypical TN that did not respond to standard medical treatments.

Patients and methods

We retrospectively studied patients who received RF thermocoagulation for treating medication resistant atypical TN from January 2014 through December 2017 in the pain management department, Akdeniz University, Antalya. The study was approved by the Akdeniz University Local Research Ethics Committee. We collected the following data from our electronic medical record: patient demographics, neurological examination, MRI findings, pain scores before and after the procedure (Visual analogue scale), and improvement after the procedure (scored at 0 to 100%). The primary outcome measure was a 50% reduction in the severity of pain measured by VAS score. Patients were followed up for a period of 1-year duration to evaluate long-term efficacy of the procedure. Patients who did not respond were offered a second procedure to relieve their symptoms.

Our study included 19 patients with atypical TN [2]. Inclusion criteria were patients above 18 years old, not responding to carbamazepine or oxcarbazepine for not less than 6 months duration or were intolerant to medications side effects. Neurological examination did not reveal any significant correlated signs apart of some sensory deficit along mandibular and/or maxillary nerve distribution. Brain MRI of all patients did not show any clinically relevant abnormalities. Exclusion criteria included typical TN, presence of any neurological signs or MRI findings suggestive of secondary cause, and history of previous surgical interventions for trigeminal neuralgia.

Procedure

Prior to the RF thermocoagulation procedure, each patient underwent a prognostic nerve block using 0.25% bupivacaine HCL (Marcaine-Astra Zeneca). Those who showed > 50% improvement in pain were eligible for RF thermocoagulation. During the RF procedure, the head of every patient was fixed, and no sedation was administered in order to be able to distinguish the affected branch of the trigeminal nerve. All the patients were cannulated, and vital data monitoring was performed throughout the procedure. The injection site was sterilized and draped.

The foreman ovale was identified with a C-arm fluoroscopy. The skin at the entry point was infiltrated with lidocaine HCL (Jetokain-Adeka) and a 2-mm active-ended RF electrode (Trigeminal RF electrode 2 mm-Cosman) was inserted and advanced parallel to the axis of the fluoroscopy till passing the foramen ovale border (Fig. 1). Aspiration was done. Test stimulation was applied at 2 Hz, 0.1–1.5 V for motor stimulation and 50–100 Hz, 0.1–1.5 V for sensory stimulation with observing movement and sensory changes described by the patient in the corresponding dermatome. After confirming the position of the electrode, radiofrequency thermocoagulation was applied at 70 °C for 90 s, then the needle was removed, and an ice pack was applied on the face. The patient was kept under observation for 2 h.

Fig. 1
figure 1

a Submental view of the foramen ovale and b lateral view to confirm the depth of the needle insertion

Full size image

Data analysis

Analysis was done in SPSS Version 22 (IBM Corporation, Armonk, NY) using one-way ANOVA for continuous outcome variables, the Pearson correlation coefficient, and the χ2 test for dichotomous outcome variables.

Results

A total of 19 patients were recruited into the study. Females outnumbered males (15 female patients, 79%) versus (4 male patients, 21%). Most of our studied population (16 patients, 79%) had right-sided trigeminal pain. Other patient characteristics are shown in Table 1.

Table 1 General characteristics of the study population
Full size table

There was more than 50% improvement in VAS score (16 patients, 79% versus 3 patients, 21%) (p < 0.05). Age was the only statistically significant factor. We found that older patients showed a better improvement regarding VAS score (p < 0.05). On the contrary, sex, the side of the trigeminal pain, and the trigeminal nerve branch and/or number affected revealed no statistical significance (p > 0.05).

Regarding complications, only one patient (5%) developed mild facial edema that subsided spontaneously within a few days, yet none of the studied patients developed any major adverse events.

Discussion

Radiofrequency thermocoagulation has been proven to be safe and effective in treating different chronic pain disorders. It has been widely used in the treatment of refractory TN in the past decade as early pain relief can be attained in 98% of patients [4].

In our study, atypical TN was statistically more common among females (16 patients, 79%). Gender was proven to play an important role in the incidence of TN as female predominance was demonstrated by many reviewers [1, 16, 17]. Our patients’ peak age of disease onset was between the sixth and seventh decades of life. This trend was confirmed by multiple previous studies. Accordingly, it is fundamental to perform thorough neurological assessment to exclude associated diseases in patients under 40 years of age [1, 18,19,20,21]. Using MRI, a study documented radiologically that women and elderly patients have significantly smaller trigeminal nerve volumes compared to men and young candidates which can be considered as a cofactor for TN [22].

In our study population, the right side was more affected than the left (13 patients, 68.5% versus 6 patients, 31.5%, respectively). This may be attributed to the anatomical fact that foramen rotundum and foramen ovale are usually narrower on the right side [16, 23,24,25]. The mandibular and/or maxillary branches were equally affected. This disease predilection pattern conforms with that of other studies [16, 17, 26, 27].

RF is the most common percutaneous procedure used to treat typical TN and offers the highest rate of efficiency (90–100%) and complete pain relief [4, 28,29,30,31,32,33,34,35,36,37]. Similarly, in our study, RF showed high efficiency (p < 0.05) in pain relief in 16 patients and only 3 patients (21%) did not reach our required > 50% pain improvement in VAS score. Few previous case reports revealed similar results in cases of atypical TN [14, 15].

Statistical analysis revealed a significant relationship between post RF pain relief and age, as older patients showed higher improvement in pain severity following the procedure. To our knowledge, there are no studies that evaluate this relationship but most studies recommend RF as the first line of treatment for medication refractory TN [5, 8, 14, 27].

Our study was limited by the number of patients and would benefit from a larger sample. Including more pain and patient’s satisfaction scores would be favorable in confirming the results.

In conclusion, this study suggests that RF thermocoagulation is an effective and relatively safe procedure for alleviating atypical facial pain. If confirmed in other studies, this will have important implications for the management of patients with atypical TN.