Idiopathic facial paralysis, also known as Bell’s palsy, is a neurological condition that leads to sudden, unilateral facial paralysis or muscle weakness [1] and is the most common type of acute peripheral mononeuropathy [2], with an annual incidence ranging from 11.5 to 53.3 cases per 100,000 individuals in various populations [3]. Despite this prevalence, the cause of Bell’s palsy remains largely idiopathic, with viral infections, particularly herpes simplex virus, being implicated as potential triggers [4].

This unclear etiology results in the development of multidisciplinary approaches for treatment, ranging from the administration of corticosteroids and antiviral medications to the use of physical therapies and alternative methods, such as acupuncture [4]. Multiple clinical practice guidelines (CPGs) from various nations and societies have been established for managing Bell’s palsy to ensure standardized, evidence-based care that can hasten recovery and restore facial function.

Idiopathic facial nerve palsy is known to have a favorable prognosis, but up to 30% of patients may experience sequelae of facial palsy even with appropriate treatment, such as lasting facial asymmetry, synkinesis, or contracture [5]. Consequently, it is important to minimize nerve damage and to ensure prompt and early recovery. While the administration of high-dose steroids within the first 72 hours is strongly advised, no universally accepted treatment exists beyond this initial intervention. In clinical practice, various treatment methods, including acupuncture, exercise, and electric therapies, are implemented. Reflecting the current emphasis on multidisciplinary treatments in addition to steroid administration, CPGs for peripheral facial nerve paralysis, developed in various countries and professional societies, suggest complementary treatments; however, a definitive treatment protocol has yet to be established.

Among the myriads of treatment options for Bell’s palsy, electrical stimulation therapy has garnered both interest and controversy, as this treatment approach aims to encourage nerve regeneration and maintain muscle mass and contractility by delivering electrical currents to the affected facial muscles [6]. However, concerns still remain regarding the insufficient high-quality evidence to support its widespread adoption [7-9] and about the potential adverse effects of the overstimulation of the facial nerve, which could exacerbate synkinesis or other complications [10]. The inconsistencies in the treatment protocols lead clinicians to disagree on the effectiveness and safety of electrical stimulation in treating facial paralysis [11], causing uncertainty to patients on which therapy to pursue and potential delays in receiving the most effective care.

The present study aims to conduct a systematic review of the existing CPGs related to the application of electrical stimulation in treating Bell’s palsy. We will summarize the guidelines from various countries and medical societies, assess the quality of the recommendations, and critically review the existing guidelines on electrical stimulation therapy for idiopathic facial paralysis. The present review article seeks to identify the gaps in current knowledge regarding the management of Bell’s palsy, providing clinicians with reliable insights for selecting appropriate treatments in clinical practice.

1. Protocol and registration

The protocol for this systematic review has been submitted to the international databases of prospectively registered systematic reviews, under the registration number CRD42024576603. This protocol adheres to the guidelines outlined in the Preferred Reporting Items for Systematic Review and Meta-Analysis Protocols (PRISMA-P; Supplementary Table 1) [12]. We employed the PICAR framework, encompassing the Population with the clinical condition, Intervention, Comparator or no comparator, Attributes of eligible CPGs, and Recommendations characteristics format [13] to develop the research question and guide both data collection and data extraction. The research questions for this systematic review are as follows: “In the management of idiopathic facial paralysis, how is electrical stimulation treatment recommended according to the currently published CPGs?” and “If the recommendations differ between CPGs, what are the contributing factors or evidence base for each recommendation?”.

2. Literature search

A systematic literature search will be conducted using the MEDLINE via PubMed, EMBASE, Cochrane Library, PEDro, CNKI, and CiNii databases. Additional evidence-based or CPG-related databases that will be searched include the Guidelines International Network, Korean Medical Guideline Information Center, and National Clearinghouse for Korean Medicine.

The search in each database will use the following terms: “Idiopathic facial paralysis,” “Bell’s palsy,” and “clinical practice guidelines”. The detailed search strategy in MEDLINE is presented in Table 1. The literature published from January 2004 to May 2024 will be searched; since the Appraisal of Guidelines for Research and Evaluation (AGREE) tool was first developed in 2004, CPGs developed subsequently should have adhered to the quality assessment criteria established by the AGREE Group.

Table 1 . Search strategy for MEDLINE via PubMed.

Number	Search terms
#1	Facial paralysis[MeSH Terms]
#2	Bell’s palsy[MeSH Terms]
#3	Idiopathic facial palsy[MeSH Terms]
#4	((bell*[Title/Abstract] OR facial[Title/Abstract] OR “idiopathic facial”[Title/Abstract]) AND (pals*[Title/Abstract] OR paralys*[Title/Abstract] OR paresi*[Title/Abstract]))
#5	#1 OR #2 OR #3 OR #4
#6	guideline[MeSH Terms]
#7	consensus[MeSH Terms]
#8	recommendation
#9	CPG
#10	clinical practice guideline[MeSH Terms]
#11	(guideline*[Title/Abstract]) OR (consensus[Title/Abstract]) OR (recomm*[Title/Abstract])
#12	#6 OR #7 OR #8 OR #9 OR #10 OR #11
#13	#5 AND #12

CPG, clinical practice guideline..

3. Eligibility criteria

Two reviewers will independently examine and select the CPGs according to the inclusion and exclusion criteria. We will include the CPGs or consensus statements on the management of idiopathic facial paralysis that include statements on the use of electrical stimulation. In the present review, electrical stimulation treatment is defined as ‘an application of an electrical current to the body from an external device through either transcutaneous or invasive electrodes [14].’ We will consider the CPGs in any language, and if two or more CPGs were developed from a single society, the most recently updated CPG from each organization will be included.

The documents where the full text is unavailable and guidelines without definite statements of the recommendation grade concerning electrical stimulation will be excluded. Recommendations on secondary facial paralysis and facial paralysis in specific conditions, such as pregnancy or pediatry, will also be excluded.

4. Study selection

Following the completion of searches, the references will be managed in EndNote 21.3 (Clarivate Analytics), with the removal of duplicates. The PICAR format will be employed to define the eligibility criteria of the CPG and CPG recommendations (CPGRs). Two independent reviewers (HJ and SL) will screen the references by their titles and abstracts to verify their eligibility, and articles identified as relevant will be included in the next phase, where the same reviewers will independently assess a full-text review of the CPGs to ensure they meet the eligibility criteria. Any disagreements that cannot be resolved by consulting a third reviewer will be addressed through a discussion. The PRISMA flow diagram (Fig. 1) [15] displays the study selection procedure.

Figure 1. Preferred Reporting Items for Systematic Review and Meta-Analysis flow diagram of the study selection. Revised from the article of Page et al. (BMJ 2021;372:n71) [15].

5. Data extraction

Two reviewers will independently carry out the data extraction process, ensuring that all relevant data are systematically collected, and the data will be extracted and provided in the form of tables using a Microsoft Excel spreadsheet (Microsoft Office LTSC Professional Plus 2021, Microsoft Corporation). The following details from each CPG will be extracted: title, year of publication, developers (organization), country or region of development, target users, and funding source. Additionally, the following information concerning electrical stimulation will be extracted from each CPG: definition and type of electrical stimulation; recommendation grade made by the CPG; evidence supporting the recommendation; whether it is derived from randomized clinical trials or consensus among experts; specific applied point or parameters of the stimulation; and treatment sessions or intervals.

6. Quality appraisal of the clinical practice guidelines and recommendations

For the CPGs to be effective and reliable, it is essential to apply appropriate methodologies and rigorous strategies throughout the development process [16]. The AGREE instrument is a widely recognized tool designed for the systematic evaluation of CPGs. Its comprehensive and structured approach to assessing the quality of CPGs ensures that both the methodological rigor and practicability of CPGs are thoroughly evaluated [17,18]. This tool has been validated and is commonly used in systematic reviews of clinical guidelines, making it a reliable choice for the present study.

The Appraisal of Guidelines for Research and Evaluation II (AGREE-II) instrument, an updated version of the original AGREE instrument, comprises the following six domains: (1) scope and purpose; (2) stakeholder involvement; (3) rigor of development; (4) clarity and presentation; (5) applicability; and (6) editorial independence [19]. Both AGREE-II and Appraisal of Guidelines for Research and Evaluation-Recommendation Excellence (AGREE-REX) quality appraisals adopt a Likert scale ranging from 1 (strongly disagree) to 7 (strongly agree) [18]. A score of 1 should be assigned if the information is irrelevant or inadequately reported, whereas a score of 7 is appropriate when all criteria and considerations are fully satisfied [20]. Two reviewers will assess each included guideline independently and determine the scores, resolving scoring discrepancies through discussions if needed. The calculation for the score of each domain will proceed as follows:

In establishing the AGREE instrument, the AGREE-II user manual [19] defines no specific guidance or threshold score to evaluate CPG as having high, moderate, or low quality due to a lack of empirical data. Nonetheless, the manual emphasizes the need to clarify the quality thresholds between the panels before beginning the AGREE-II appraisals [19]. Accordingly, the quality thresholds established from other appraisals of CPGs were referred to, and the criteria used by Shahid et al. [21] will be adopted in the present review; the quality of the CPG is evaluated as “high” (≥ 5 domains scoring > 60%), “average” (3 or 4 domains scoring > 60%), or “low” (≤ 2domains scoring > 60%).

While AGREE-II assesses the overall process and development of guidelines, the AGREE-REX instrument, newly designed in 2019, is a complementary tool of AGREE-II, concerning specifically on the quality and implementability of the recommendations within CPGs. The AGREE-REX instrument includes the following three key domains: (1) clinical applicability, (2) values and preferences, and (3) implementability [22]. Prior to commencement, both reviewers will complete the training modules and be acquainted with the instructions for assessing each item in the AGREE-II and AGREE-REX user manuals [23].

7. Data synthesis and analysis

Descriptive analyses will be conducted about the general characteristics of each CPG, and the assessment of each CPG using the AGREE-II and AGREE-REX instruments will be organized per domain. All data will be recorded and managed using Microsoft Excel (Microsoft Office LTSC Professional Plus 2021), and the results will be summarized in a table format. We will also discuss the reasons behind the varying recommendations for specific electrical stimulation therapies on idiopathic facial paralysis, considering the publications’ characteristics and the strength and quality of the evidence base.

The Institute of Medicine defines CPGs as “statements that include recommendations intended to optimize patient care that are informed by a systematic review of evidence and an assessment of the benefits and harms of alternative care options” [24]. Beyond their contribution to aiding clinical decisions, CPGs are utilized to assist policymakers in the allocation of healthcare resources [24]. For a single disease, multiple CPGs have been published by diverse nations and organizations in recent decades, but unfortunately, they can differ in terms of their methodological quality, and the recommendation for a treatment can alter between CPGs as evidence accumulates and updates.

Electrical stimulation has gained recognition as an appropriate tool for treating partial nerve paralysis to minimize muscle atrophy and maintain muscle contractility [6]. However, existing data are conflicting on whether the efficacy of electrical stimulation in idiopathic facial palsy is beneficial [6,25], has no substantial effect [26], or may inflict harm [27]. This discrepancy in the efficacy of electrical stimulation as a therapeutic intervention can lead to a lack of standardization of treatment protocols, leading to the implementation of diverse approaches in managing Bell’s palsy among different clinicians. Ultimately, the varied perspectives on the effectiveness of electrical stimulation highlight the need for a thorough review of currently published CPGs to ensure that healthcare professionals have the most up-to-date and evidence-based treatment recommendations.

Previously, Luu et al. [17] appraised the CPGs for idiopathic facial paralysis using the AGREE-II instrument, concluding that the current guidelines for diagnosing and managing idiopathic facial paralysis require improvement in their methodological quality, specifically in the domains of “rigor of development,” “stakeholder involvement,” and “applicability.” Several updated versions of CPGs have been published afterwards, suggesting the necessity of reviewing the currently published CPGs.

Phillips et al. [28] emphasized the importance of examining several factors, including geographical location, local health care systems, and cultural and economic factors, which could be the underlying causes of conflicting recommendations between various publications. Their systematic review of CPGs for knee osteoarthritis [28] revealed that the variations in recommendations often arise from the different subsets of evidence reviewed by each guideline. The subset of evidence used in formulating CPGs is therefore crucial, impacting the relevance and applicability of each recommendation. The present review not only will examine the guidelines themselves but also will delve into specific recommendations to identify the potential biases and ensure that the guidelines are based on balanced and relevant data.

The present review aims to provide a systematic overview of the current CPGs on idiopathic facial paralysis and to further identify the consistency of the recommendation grade provided by each CPG on the electrical stimulation treatment. This review will also evaluate the evidence base of each recommendation, identifying the reasons for the conflicting recommendations if needed. This could aid in establishing the methodological standards for developing CPG and formulating CPGRs. We anticipate that this review will reveal the variations in CPGRs across different publications, which can be critical not only for clinicians in deciding treatment but also for CPG developers and policymakers.

Supplementary data is available at https://doi.org/10.13045/jar.24.0043.

Conceptualization: HJ, SL. Data curation: HJ, SL. Formal analysis: HJ, SL. Investigation: HJ, SL. Methodology: HJ, SL. Project administration: All authors. Supervision: YK, SL. Validation: All authors. Visualization: HJ, SL. Writing – original draft: HJ. Writing – review & editing: YK, TK, SN, SL, YSK.

The authors have no conflicts of interest to declare.

None.

This research did not involve any human or animal experiments.