FormalPara Key Summary Points

Facial paralysis is a facial function disorder associated with significant psychosocial impact, communication disorders, aesthetic disfigurement, and poor outcomes regarding quality of life. Although we recognize that there can be some self-recovery, still some patients have residual facial paralysis, especially after herpetic facial paralysis with pain, which has a greater impact on patients

Percutaneous stylomastoid foramen pulsed radiofrequency combined with steroid injection for treatment of intractable facial paralysis after herpes zoster can not only relieve pain but also improve facial paralysis. This retrospective study evaluated the safety and efficacy of this new technique and hopes to provide a new treatment method for severe facial paralysis or cases where drugs have failed

Percutaneous stylomastoid foramen pulsed radiofrequency combined with drug injection of the facial nerve for treatment of intractable facial paralysis after herpes zoster is a minimally invasive technique with high rates of success, safety, and effective outcomes

Percutaneous stylomastoid foramen puncture with blunt radiofrequency needle can decrease nerve injury and be used adjacent to facial nerve therapy. It is a potential therapeutic option specially for cases of facial paralysis of herpes zoster with long history even for those patients who have severe facial paralysis and failed recovery after oral medication and physiotherapy

Introduction

Facial paralysis (FP) is a facial function disorder associated with significant psychosocial impact, communication disorders, aesthetic disfigurement, and poor quality of life outcomes [1,2,3]. Its etiology is attributed to trauma, infection, neurologic, metabolic, genetic, vascular, and neoplastic disorders as well as toxic, idiopathic, and iatrogenic causes [4]. Most FP patients are diagnosed with Hunt’s syndrome and Bell’s palsy. Inflammation and edema resulting in FP are the most common causes [5,6,7]. Orally administered corticosteroids have been shown to reduce inflammation and edema.

However, in some cases, especially in patients with facial neuritis secondary to herpes virus infection, accompanied by obvious pain, early oral corticosteroid administration does not relieve facial paralysis. Moreover, long-term administration of oral corticosteroids is correlated with some side effects; thus, these patients face long-term consequences of facial paralysis. Long-term loss of function of facial nerves has implications beyond the associated functional deficits, with significant psychosocial implications [8, 9]. A study involving 42,866 patients with a formal diagnosis of Bell’s palsy showed that 1.4% received surgery, 0.9% received botulinum toxin treatments, and 32.4% received rehabilitation services [10]. Therefore, oral medication alone does not alleviate facial paralysis in all populations. Percutaneous facial pulsed radiofrequency (PRF) is a minimally invasive approach that uses electrodes to stimulate facial nerves [11].

Through radiofrequency needle stimulation, nerve conduction can be stimulated through pulsed currents, and neurotrophic drugs as well as hormones can be injected around the facial nerve to directly produce the desired effects. We retrospectively investigated the safety and effectiveness of transcutaneous facial nerve pulse combined with drugs for treatment of stubborn facial paralysis after herpes zoster (HZ).

Methods

Ethical Approval

The Medical Ethics Committee of the Affiliated Hospital of Jiaxing University approved this study (LS2019-013). All participants agreed to the study procedures and permitted the sharing of their imaging data (including pre- and post-treatment images) for future studies and publications. This study was conducted in accordance with the Declaration of Helsinki. Signed informed consent was obtained from all patients.

Patients

A total of 43 patients with a history of facial paralysis after HZ for > 1 month and in whom other treatments had failed were recruited from the Pain Department of the First Hospital of Jiaxing between May 2020 and May 2022. All patients underwent computed tomography (CT)-guided percutaneous stylomastoid foramen pulsed radiofrequency of the facial nerve. All participants were required to sign informed consents before inclusion in this study.

Inclusion and Exclusion Criteria

The inclusion criteria were: (1) patients with clinically diagnosed facial paralysis after HZ; (2) patients who failed to recover after 1 month with other therapies; (3) patients aged > 18 years; (4) those who agreed to undergo pulsed radiofrequency modulation of the facial nerve; (5) patients who agreed to a postoperative telephone follow-up. The exclusion criteria were: (1) patients with facial skin infections or tumors; (2) those with severe disorders or major systemic insufficiency; (3) patients with trauma-induced nerve rupture; (4) patients with bad coagulation functions; (5) patients that were allergic to related drugs; (6) patients who refused the operation itself and who were unwilling to accept any complications or had missing data. This study was performed in accordance with the Declaration of Helsinki. All patients agreed to sign the informed consent form prior to their inclusion in this study.

Surgical Procedures

Surgical procedures were performed under CT guidance. The patients were laid in lateral positions on the bed with the affected side up. Oxygen intake and electrocardiogram (ECG) monitoring were continuously performed. The positioning grid was fixed on the affected facial side by an adhesive tape (Fig. 1) and CT scan imaging was carried out. The puncture path targeting the stylomastoid foramen was via the anterior (Fig 2-1) or posterior (Fig. 3-1) approaches, according to CT scan imaging. Appropriate local anesthesia and sedation were performed before needle insertion. Soft insertion of the needle was essential to avoid facial nerve injury. We used specially designed blunt needles (Fig. 4) in our research, which can avoid nerve injury from the injection. When the stylomastoid foramen was reached (Figs. 2-2, 3-2), a PRF probe was induced. Parameters for the sensory test (voltage < 0.5 V and frequency 50 Hz) and exercise test (voltage < 0.5 V and frequency 2 Hz) were set, which could induce soreness, swelling, numbness, or facial fibrillation as well as pulsation of trunk muscle fibers in innervated areas considered positive. Temperature, time, pulse width, and frequency were set at 42 °C, 300 s, 20 ms, and 2 Hz, respectively [12], while PRF voltage was not > 50 V [13]. Based on standard parameter pulses, we added the maximum tolerable voltage exercise stimulation, and patients experienced obvious muscle contractions in innervated areas for 5 additional min [11]. At the end of the above procedures, the electrode core was pulled out, and 2 ml treatment solution (0.25% lidocaine hydrochloride, 0.5 ml contrast agent, 1 mg compound betamethasone, and 1 mg mecobalamin) was injected after withdrawing the puncture needle with no blood, gas, or liquid (Figs. 2-3, 3-3). Specially designed blunt radiofrequency puncture needles made by Fuerte Company of Zhejiang Province (Fig. 4) were used; they do not have a sharp slope and can avoid nerve damage during the puncture process.

Fig. 1
figure 1

Patient in the lateral position with the surgical site exposed and computed tomography (CT) scan; the display grid is positioned anterior and posterior to the patient’s ear. CT computed tomography

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Fig. 2
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2–1: Puncture path via the anterior approach targeting the stylomastoid foramen. Black arrow shows target point. 2–2: Intraoperative CT scan of the RF needle reaching the stylomastoid foramen using the anterior approach. Black arrows show RF needle imaging. 2–3: Compound liquid was injected after RF procedure. Black arrows show contrast agent diffusion. CT computed tomography; RF radiofrequency

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Fig. 3
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3–1: Puncture path via the posterior approach targeting the stylomastoid foramen. Black arrow shows target point. 3–2: Intraoperative CT scan of the RF needle reaching the stylomastoid foramen using the posterior approach. Black arrows show RF needle imaging. 3–3: Compound liquids were injected after RF procedure. Black arrows show contrast agent diffusion. CT computed tomography; RF radiofrequency

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Fig. 4
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Specially designed blunt needles used in our research which minimize nerve injury when inserting the needle

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Observation Indices

The collected data included:

• General patient information (Table 1).

Table 1 Patient characteristics
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• The NRS scores at different times (T0: pre-procedure, T1: 1 day post-procedure, T2: 2 weeks, T3 and T4: 4 and 12 weeks post-procedure) (Table 2, Fig. 5A).

Table 2 Comparison of pre- and postoperative facial paralysis NRS scores
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Fig. 5
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A Comparison of NRS scores before and after treatment. B Comparison of facial paralysis grading before and after treatment. Notes: **p < 0.050, ***p < 0.0001. NRS, numerical rating scale; T0 preoperation; T1 1 day after operation; T2 2 weeks after operation; T3 4 weeks after operation; T4 12 weeks after operation

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• Facial paralysis grading according House-Brackmann grades at T0, T1, T2, T3, and T4 (Table 3).

Table 3 Comparison of pre- and postoperative facial paralysis grades
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• Presence/absence of post-procedural complications (Table 4).

Table 4 Intraoperative and postoperative complications
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Statistical Analysis

SPSS26.0 (IBM, Chicago, IL, USA) was used to analyze the data. The Shapiro-Wilk test was used to determine whether the measurement data obeyed a normal distribution, and the results were expressed as the mean ± standard deviation (SD), while the non-normally distributed data were expressed as the median (IQR). A paired sample t-test was used to compare the differences among measurement data, and the chi-square test was used to compare the differences between counting data. We used the Wilcoxon test to analyze the non-normally distributed data. The Kruskal-Wallis test was used to analyze the NRS score and facial paralysis grading at each time interval after the operation. Multiple comparisons were performed by the Bonferroni test, and the significance level was corrected. A violin plot was used to describe the changing trends in NRS score and facial paralysis grade.

Results

Clinical Characteristics of Patients

A total of 43 patients [17 male and 26 female; median IQR 59 (52–69) years, range 24–76 years] were enrolled in this study. All patients had facial paralysis disease after HZ for > 1 month and had had other prior treatments that had produced no effect. All patients were followed up by telephone. The general characteristics of the patients are shown in Table 1.

Safety and Efficacy of the Puncture Path

A total of 43 cases successfully finished the CT-guided percutaneous stylomastoid foramen pulsed radiofrequency of the facial nerve. Specially designed blunt needles (Fig. 4) that minimize nerve injury during needle insertion were used in our research. The puncture path targeting the stylomastoid foramen was via the anterior approach for 36 patients (Fig. 2-2) and the posterior approach for 7 cases (Fig. 3-2). Both approaches can obtain feeling by pulsed radiofrequency; some can see tiny muscle tremors. There were obvious muscle contractions in the innervated areas during the additional 5 min maximum tolerable voltage exercise stimulation.

NRS Scores and House-Brackmann Grades Before and After Treatment

The NRS score collection times were: T0: pre-procedure, T1: 1 day post-procedure, T2: 2 weeks, T3 and T4: 4 and 12 weeks post-procedure. The scores were 2.69 ± 2.213, 0.700 ± 0.939, 0.580 ± 1.006, 0.440 ± 0.908, and 0.260 ± 0.759, respectively (Table 2). Differences in NRS scores between T0 and T1-4 were significant (Table 2), but those between T1 and T2-4 were not significantly different.

The six House-Brackmann grades (I, II, III, IV, V, VI) were determined at different times: T0: pre-procedure, T1: 1 day post-procedure, T2: 2 weeks, T3 and T4: 4 and 12 weeks post-procedure. The patients felt better at T1 after treatment and gradually improved at each time point, but recovery slowed after T3 (Table 3, Fig. 5B).

Intra- and Postoperative Complications

Follow-up assessment revealed that six patients developed mild numbness, nine patients showed muscle tension, and one patient had facial stiffness. During surgery, there was no intravascular drug injection; no nerve injuries or local anesthetic poisoning were reported, and spinal anesthesia was not performed (Table 4).

Discussion

FP affects facial appearance and seriously impacts the patients’ quality of life. Bell’s palsy is the most common cause of acute facial palsy and can affect all age groups. However, its incidence rate is relatively low in children aged ≤ 10 years and in older adults [15]. Ramsay Hunt syndrome is the second most common cause of facial palsy [15, 16]. Our study assessed the treatment of the facial paralysis after HZ.

The etiology of Bell's palsy is associated with viral infections [17,18,19]. Varicella-zoster virus (VZV) infections in patients’ face should be confirmed in patients with peripheral facial paralysis and is believed to be a consequence of herpes simplex virus (HSV) activation. In Ramsay Hunt syndrome, facial paralysis is accompanied by herpes infections of the ear and face. [20]. Therefore, antiviral medications are the first choice therapeutic options for Bell’s palsy or Ramsay Hunt syndrome. Oral glucocorticoids can decrease facial nerve inflammation or edema, while surgery can alleviate facial nerve compression [21]. In this study, percutaneous stylomastoid foramen steroid injection combined with pulsed radiofrequency of the facial nerve relieved pain and decreased edema as well as inflammation of HZ.

Percutaneous PRF is a minimally invasive procedure that uses electrodes to stimulate pathological nerves [11]. Mechanistically, PRF is a temperature-independent neuromodulatory process that alters synaptic transmission and pain signaling via emission of electric fields, with no to minimal resultant tissue destruction. It has been reported that PRF can exert destructive effects on the mitochondria, microfilaments, and axonal microtubules, with the greatest destruction in nociception mediating unmyelinated type C fibers, followed by myelinated type A-beta and type A-delta fibers [22]. In this study, facial paralysis after HZ benefited from this mechanism, which also resulted in pain relief. The specially designed blunt puncture needle does not have a sharp slope to avoid nerve damage during the puncture process (Fig. 4). Furthermore, PRF also relieved neuralgia via enhancement of descending serotonergic and noradrenergic inhibitory pathways [23]. We also used high-voltage motors to stimulate the facial nerves by pulsed radiofrequency. Facial muscle twitch gradually increased as voltage increased, which restored electric conduction of facial nerves and helped with muscle contraction. More than 79% of study participants reported that their muscle tightness was greatly relieved. This electric motor stimulation of adjacent nerves can exert similar effects in nerve or muscle massages. Considerations regarding this stimulation are: (1) Exercise stimulation of facial nerve regions may lead to recovery of innervational muscle functions; (2) muscle contraction and relaxation may lead to relysis of surrounding tissues; (3) rhythmic muscle contractions and nerve discharge may lead to acceleration of peripheral microcirculation and decreased local edema as well as reduced peripheral nerve compression [11]. These outcomes have not been reported in previous percutaneous stylomastoid foramen therapy. The greater the stimulation of the nerve by needle puncture is, the greater the decrease in edema of the nerve capsule.

In clinical radiology, compared to fluoroscopy and ultrasound, CT-guided procedures have been accepted because of their clinical accuracy and safety [24,25,26]. In our study, CT-guided percutaneous stylomastoid foramen puncture increased accuracy and avoided nerve damage because the needle could be consciously and slowly inserted in the area around the nerve. Furthermore, specially designed blunt needles (Fig. 4) were used in our research, which minimized nerve injury when the needle was inserted. We selected the preauricular or retroaurural approaches, both of which can reach close to the stem facial nerve, increasing the close contact between pulse radiofrequency and the nerve, thereby producing therapeutic effects. The retroaurural approach is usually performed under x-ray or ultrasound. In our clinical practice, the preauricular approach under CT guidance reaches the target more easily and accurately (Fig. 1).

Glucocorticoids for facial paralysis should be administered orally and early; however, they are metabolized throughout the body and can affect many other organs, resulting in adverse effects, including osteoporosis or necrosis of the femoral head of elderly persons. Soluble glucocorticoids can be safely used locally [27] and injected directly around the nerve to quickly reduce inflammation and eliminate edema. Thus, there is less systemic absorption. We used a non-particulate glucocorticoid preparation in this study. When the tip was near the nerve and after electrical stimulation, corticosteroid combined with a contrast agent and the nutritional nerve drug, B12, were administered. Such local administration increased the local target drug concentration and reduced the side effects to other organs.

In summary, CT-guided percutaneous stylomastoid foramen PRF of the facial nerve is an accurate, safe, and effective treatment option for facial paralysis, even for stubborn cases after HZ. This study provides a new treatment approach to facial paralysis, especially for refractory facial paralysis after HZ with pain and poor oral drug effects. The study provided two approaches, which are both safe and effective [23].

Limitations

Our study has some limitations that should be addressed. First, patients enrolled were from only one pain management center. Second, the patients were only followed up for 3 months. Future study should carry out research across multiple centers with a longer follow-up.

Conclusions

Percutaneous stylomastoid foramen PRF of the facial nerve for difficult facial paralysis after HZ is a minimally invasive technique with a high success rate. It is a safe and effective approach when combined with steroid injection.