Abstract
Introduction
Bell’s palsy is a peripheral facial nerve neuropathy of the facial nerve of unknown origin that primarily causes unilateral facial muscle weakness or paresis. Electroacupuncture (EA) is used clinically to treat patients with Bell’s palsy in the post-acute phase; however, high-quality evidence supporting its effect remains insufficient. This study will investigate the effects of two commonly used EA pulse patterns and explore the electromyographic characteristics of Bell’s palsy using surface electromyography as an objective assessment method.
Methods and analysis
A total of 111 patients with Bell’s palsy will be recruited from two hospitals and randomised in a 1:1:1 ratio to the sham EA, continuous-pulse EA or intermittent-pulse EA group. This patient- and assessor-blinded, parallel-group trial will include a 4-week treatment period, with assessments conducted at baseline (day 0), at the end of week 2 and at the end of week 4. An additional follow-up assessment will also be conducted at 6 months after the disease onset. The primary outcome will be the Facial Nerve Grading System 2.0 score. Secondary outcomes will include the root mean square ratio between the affected and unaffected sides, median frequency ratio between the affected and unaffected sides, Sunnybrook Grading Scale score and Facial Disability Index score. All adverse events during the trial will be evaluated. Recruitment has not started yet.
Ethics and dissemination
Ethic approval has been obtained from the Ethics Committee of the First Affiliated Hospital of Zhejiang Chinese Medical University (55) and the Ethics Committee of the Third Affiliated Hospital of Zhejiang Chinese Medical University (ZSLL-KY-2025-134). The findings of the study will be disseminated through publication in peer-reviewed journals.
Trial registration number
Keywords: Randomized Controlled Trial, Acupuncture, Electric Stimulation Therapy
STRENGTHS AND LIMITATIONS OF THE STUDY.
This study will employ surface electromyography as an objective tool to assess facial muscle characteristics in patients with Bell’s palsy.
This study will assess the effects of two distinct electroacupuncture (EA) pulse patterns in the treatment of Bell’s palsy, incorporating a sham EA control group for comparison.
This study only includes a 4-week treatment duration, which may be insufficient for patients with severe Bell’s palsy.
All participants will be recruited from two hospitals in Hangzhou, China, which may limit the generalisability of the findings to other regions.
Introduction
Bell’s palsy is a common peripheral facial nerve disorder characterised primarily by unilateral facial weakness or loss of facial muscle function of unknown aetiology.1 Some patients may also experience postauricular pain, impaired taste sensation and hyperacusis.2 The reported global annual incidence of Bell’s palsy ranges from 11.5 to 53.3 cases per 100 000 population and accounts for approximately 75% of total acute facial paralysis cases.3 4 Recovery time varies among patients approximately 10% recover fully within 3 weeks, most achieve complete recovery within 2 to 6 months and a small subset experience persistent or incomplete recovery.4 Given the considerable multidimensional burden associated with Bell’s palsy, early interventions are needed to facilitate the recovery process.5
Early corticosteroid administration during the acute phase of Bell’s palsy improves prognosis in adults.6 However, effective strategies for promoting facial nerve recovery after the acute phase remain limited, creating a substantial challenge in clinical practice.7 8 Acupuncture is a complementary and alternative therapy used to treat patients with Bell’s palsy.9 Among acupuncture modalities, electroacupuncture (EA), which combines traditional needling with electrical stimulation, has received considerable attention for this condition.10 Although EA use in the early stage of Bell’s palsy remains controversial,11 its application in the post-acute phase has been widely reported, and several studies suggest beneficial effects on recovery from Bell’s palsy.12 13 In addition, some studies indicate that EA may be more effective than manual acupuncture.14 15 However, the current evidence for EA in Bell’s palsy is limited by low study quality and a lack of sham-controlled trials.12 16 Notably, variations in EA parameters may have differential effects on neuromuscular function: low-frequency continuous-pulse EA at 2 Hz may facilitate nerve regeneration, whereas medium-frequency intermittent-pulse EA at 30 to 50 Hz may enhance muscle size and strength.17 18 Nevertheless, the therapeutic effects of both EA pulse patterns in patients with Bell’s palsy remain unclear.
Surface electromyography (sEMG) uses surface electrodes to detect electrical signals generated by specific muscles during contraction and records of muscle activity that may be too subtle to observe visually.19 This technique is widely used to assess muscle strength, endurance and neuromuscular control, providing insight into the physiological or pathological state of muscles.20–22 In recent years, sEMG has gained attention in facial paralysis research as an objective method for assessing both symptom severity and treatment response in Bell’s palsy.23–25
To investigate the effects of the continuous-pulse and intermittent-pulse EA in the post-acute phase of Bell’s palsy, we will conduct a three-arm, sham-controlled trial using sEMG as an objective outcome indicator.
Methods and analysis
Study design
This study is designed as a patient- and assessor-blinded, three-arm, parallel-group randomised controlled trial. Eligible patients will be randomly assigned in a 1:1:1 ratio to the sham EA, continuous-pulse EA or intermittent-pulse EA group. Participants will receive 4 weeks of treatment and outcomes will be assessed using clinical rating scales and sEMG. A summary of the trial design is presented in figure 1.
Figure 1. Trial procedure. EA, electroacupuncture; FDI, Facial Disability Index; FNGS, Facial Nerve Grading System; MDF, median frequency; RMS, root mean square; SBGS, Sunnybrook Grading Scale; sEMG, surface electromyography.
Study setting and enrolment
This trial will be conducted at two centres, the First Affiliated Hospital of Zhejiang Chinese Medical University and the Third Affiliated Hospital of Zhejiang Chinese Medical University. Participants will be recruited through printed posters displayed in outpatient departments and online posters distributed via social media platforms. Trained researchers who are not involved in intervention delivery or outcome assessment will screen potential participants for eligibility and obtain written informed consent (online supplemental material). After written informed consent is obtained, participants will receive education regarding Bell’s palsy and acupuncture therapy and will then be randomly assigned to one of three groups. During the study period, participants will receive the intervention assigned to their group and will not receive any additional intervention other than those specified in the protocol. The number of treatment sessions received by each participant will be recorded. Participants who receive interventions that violate the protocol, withdraw voluntarily or cannot continue participating for other reasons will be excluded from the per-protocol (PP) analysis set but will remain included in the intention-to-treat (ITT) analysis set.
Study registration and protocol version
The trial has been registered at ClinicalTrials.gov (ID: NCT07514117), with the latest version published on 29 April 2026. The current protocol is V.1.0, dated 29 April 2026.
Eligibility criteria
Inclusion criteria
Participants will be included if they meet all of the following criteria: (1) diagnosis of Bell’s palsy by a neurology clinician, with brain CT and/or MRI excluding central nervous system lesions associated with facial palsy; and (2) disease duration from 21 days to 3 months, inclusive; and (3) age 18–70 years; and (4) voluntary participation and provision of written informed consent; and (5) receipt of prednisolone during the acute phase at a daily dose of 30–60 mg for at least 5 days.26
Exclusion criteria
Participants who meet any of the following criteria will be excluded: (1) facial paralysis caused by diseases other than Bell’s palsy; (2) previous facial paralysis; (3) facial muscle spasm, synkinesis or contracture; (4) Ramsay Hunt syndrome; (5) history of facial surgery; (6) implanted cardiac pacemakers; (7) pregnancy or lactation; (8) along with other severe uncontrolled diseases, recognition disorder, aphasia or mental disorders; (9) present with bilateral facial paralysis.
Randomisation
Eligible participants who provide written informed consent will be enrolled and assigned a unique identification number according to outpatient-visit order. To minimise selection bias and ensure balanced allocation across the study groups, stratified block randomisation will be used, with clinical centre as the stratification factor. An independent statistician who is not involved in participant recruitment, intervention implementation or outcome assessment will generate centre-specific randomisation sequences using SPSS V.29.0 (IBM, Armonk, New York, USA). Within each centre, participants will be assigned in a 1:1:1 ratio to the sham EA, continuous-pulse EA or intermittent-pulse EA group. Randomly permuted blocks with variable block sizes will be used within each centre, and the block sizes will be concealed from investigators involved in recruitment, intervention implementation and outcome assessment. A total of 111 participants will be randomised, with 37 participants allocated to each group.
Blinding and allocation concealment
Participants, outcome assessors and data analysts will remain blinded to group allocation throughout the trial. Because of the nature of the intervention, the acupuncturists who administer the treatment cannot be blinded and will know each participant’s group assignment. Independent assessors who are not involved in participant recruitment or intervention implementation will perform outcome assessments. Data analysts will use coded group labels to maintain blinding during the statistical analysis, following the principle of separation among researchers, intervention providers, outcome assessors and statisticians.
To ensure allocation concealment, an independent researcher who is not involved in participant recruitment, intervention implementation or outcome assessment will prepare group assignment cards according to the centre-specific randomisation sequences. The assignment cards will be placed into consecutively numbered, opaque, sealed envelopes for each centre. The envelopes will be identical in appearance and securely stored by designated researchers who are not involved in outcome assessment. After an eligible participant has completed enrolment, the next envelope in sequence at the corresponding centre will be opened according to the participant’s randomisation order, and the participant will be assigned to the corresponding intervention group. The allocation sequence will remain concealed until the intervention is assigned.
Unblinding of participants or outcome assessors is not anticipated and will be permitted only when knowledge of treatment allocation is necessary for urgent participant safety management. Any unblinding will be authorised by the principal investigator, documented in the study records and restricted to the minimum personnel required.
After completing the final treatment at week 4, participants will complete a questionnaire assessing the effectiveness of participant blinding. They will be asked which treatment they believe they received during the study: sham EA, continuous-pulse EA, intermittent-pulse EA or uncertain. Each response will be classified as correct, incorrect or unsure according to the actual randomised allocation.
Blinding evaluation
The effectiveness of participant blinding will be assessed using the Bang Blinding Index (Bang BI).27 For each treatment group, the numbers and proportions of correct, incorrect and unsure responses will also be reported. The Bang BI will be calculated separately for each randomised treatment group, with corresponding 95% CIs. The numbers and percentages of correct, incorrect and unsure responses will also be reported for each group. These findings will be used to evaluate whether participants were able to distinguish among the allocated interventions and whether participant blinding was adequately maintained.
sEMG assessment
For the sEMG assessment, participants will be instructed to enter the testing room 15 min before the assessment and to rest in a supine position on the examination bed. sEMG data will be collected using an sEMG device (Delsys Trigno, Delsys, Natick, Massachusetts, USA). A trained operator will place four pairs of electrodes on the skin over the corresponding facial muscle regions bilaterally, according to the Fridlund scheme.28 The electrode locations are shown in table 1 and figure 2. The electrode placement locations refer to the centres of the electrodes. The reference electrodes were placed over the mastoid process.
Table 1. Locations and indications of electrodes.
| Muscles for electrode placement | Electrode placement locations |
|---|---|
| Frontalis | 1 cm above the superior border of the eyebrow, on an imaginary vertical line passing through the pupil |
| Orbicularis oculi | 1 cm inferior to the lateral canthus, with the electrode oriented parallel to the lower eyelid margin |
| Zygomaticus major | At the midpoint of an imaginary line connecting the cheilion and the preauricular depression |
| Depressor anguli oris | 1 cm inferior to the corner of the mouth, with the electrode oriented parallel to the muscle fibres |
Figure 2. Illustration of the electrode positions.
Before formal testing, participants will be asked to perform several maximal voluntary contractions to become familiar with the required movements. The examiner will confirm that the electrodes are securely attached by checking the signal quality on the computer. The required movements include eyebrow raising for assessment of the frontalis, eye closing for assessment of the orbicularis oculi and grinning for assessment of the zygomaticus major and depressor anguli oris.
After participants have become familiar with the required movements, sEMG recording will be initiated. Participants will be instructed to perform eyebrow raising, eye closing and grinning with maximal effort. For each movement test, participants will remain still during the first 10 s, followed by a 2-second maximal voluntary contraction and an 8-second resting interval. This contraction and rest cycle will be repeated five times, with each movement test lasting approximately 1 min in total.
Interventions
Treatment will be administered by trained acupuncturists who hold valid acupuncture licences issued by the Ministry of Health of the People’s Republic of China and have more than 5 years of clinical experience.
Continuous-pulse EA group
For participants in the continuous-pulse EA group, acupoint selection will be based on previous studies and guided by the principle of combining local and distal acupoints.18 29 The selected acupoints will include: Cuanzhu (BL2), Sizhukong (SJ23), Yuyao (EX-HN4), QiYangbai (three points: GB14, 1 cun medial to GB14 and 1 cun lateral to GB14), Tongziliao (GB1), Quanliao (SI18), Dicang (ST4), Daying (ST5), Jiache (ST6), Jiachengjiang, Yifeng (SJ17), Sibai (ST2), Yingxiang (LI20), Taiyang (EX-HN5) on the affected side and Hegu (LI14) bilaterally. The locations of the acupoints applied are presented in table 2 and figure 3.
Table 2. Location and indication of acupoints treating Bell’s palsy.
| Acupoints | Location |
|---|---|
| Cuanzhu (BL2) | Cuanzhu is located at the medial end of the eyebrow, in the supraorbital region |
| Sizhukong (SJ23) | Sizhukong is located in the depression of the lateral end of the eyebrow |
| Yuyao (EX-HN4) | Yuyao is located at the midpoint of the eyebrow, directly superior to the pupil |
| QiYangbai (three points including GB14, 1 cun medial to GB14 and 1 cun lateral to GB14) | Yangbai is located on the forehead, 1 cun directly superior to the midpoint of the eyebrow; the supplementary acupoints were located 1 cun lateral and 1 cun medial to GB14 |
| Tongziliao (GB1) | Tongziliao is located in the lateral canthus region, approximately 0.5 cun lateral to the outer canthus |
| Quanliao (SI18) | Quanliao is located in the depression on the lower border of the zygoma |
| Dicang (ST4) | Dicang is located 0.5 cun lateral to the corner of the mouth |
| Daying (ST5) | Daying is located at the anterior border of the masseter muscle, in the depression that appears when the cheek is bulged |
| Jiache (ST6) | Jiache is located approximately one finger-breadth anterior and superior to the angle of the mandible, at the prominence of the masseter muscle when the teeth are clenched |
| Jiachengjiang | Jiachengjiang is located 1 cun bilaterally to Chengjiang (CV24). Chengjiang is located in the depression at the centre of the mentolabial groove |
| Yifeng (SJ17) | Yifeng is located posterior to the earlobe, in the depression between mandible and the mastoid process |
| Sibai (ST2) | Sibai is located directly below the pupil, in the infraorbital foramen |
| Yingxiang (LI20) | Yingxiang is located in the nasolabial groove, at the level of midpoint of the lateral border of the ala nasi |
| Hegu (LI4) | Hegu is located at the dorsum of the hand, between the first and second metacarpal bones, at the midpoint of the radial side of the second metacarpal bone |
| Taiyang (EX-HN5) | Taiyang is located in the temporal region, in the depression of approximately 1 cun posterior to the midpoint of the lateral end of the eyebrow and the outer canthus |
Figure 3. The location of acupoints of treating Bell’s palsy.
Participants will be placed in a supine position. After skin sterilisation, sterile disposable acupuncture needles measuring 0.18 mm in diameter and 25 mm in length, or 0.25 mm in diameter and 40 mm in length (Hwato Brand, Suzhou Medical Products Factory, China), will be inserted into the prescribed acupoints to a depth of 5–30 mm. The needles will then be manually manipulated to elicit the de qi sensation, which is characterised by sensations such as soreness, numbness, distension or heaviness. Needles inserted at the selected paired acupoints will be connected to an EA device using electrode clips (Hwato SDZ-IIB, Suzhou Medical Supplies, China). Four pairs of acupoints will be connected for electrical stimulation: (1) 1 cun lateral to GB14 and 1 cun medial to GB14; (2) GB1 and BL2; (3) ST4 and SI18; and (4) Jiachengjiang and ST5. In accordance with previous studies, electrical stimulation will be delivered as a continuous wave at 2 Hz for 30 min per session.18 Treatment will be administered three times per week for 4 weeks, with a total of 12 sessions.
Intermittent-pulse EA group
For participants in the intermittent-pulse EA group, the acupoint selection for manual needling, needling procedures, and acupoints used for electrical stimulation will be the same as those in the continuous-pulse EA group. Based on previous studies,29 30 electrical stimulation will be delivered as an intermittent wave at 35 Hz for 30 min per session. Treatment will be administered three times per week for 4 weeks, for a total of 12 sessions.
Sham EA group
For participants in the sham EA group, non-acupoint locations approximately 5 mm away from the corresponding acupoints used in the continuous-pulse EA and intermittent-pulse EA groups will be selected.31–33 Superficial needling will be performed at these non-acupoints to a depth of 1–2 mm, without manual manipulation or intentional elicitation of the de qi sensation. EA devices will be connected to four paired points through specially customised wires without internal conductors: (1) non-acupoints near 1 cun medial to GB14 and 1 cun lateral to GB14; (2) non-acupoints near BL2 and GB1; (3) non-acupoints near ST4 and SI18; and (4) non-acupoints near Jiachengjiang and ST5. Needles will be retained for 30 min per session. Treatment will be administered three times per week for 4 weeks, for a total of 12 sessions.
Outcome measures
Participants in all groups will be assessed at baseline (day 0), at the end of week 2 (treatment), and at the end of week 4 (treatment), with an additional follow-up assessment conducted at 6 months after the disease onset. Clinical rating scales and sEMG measurements will be performed by two different blinded evaluators. The trial schedule is presented in table 3.
Table 3. Schedule of enrolment, treatments and assessment.
| Baseline | Treatment | Follow-up | ||||
|---|---|---|---|---|---|---|
| Time | Day 0 | Week 1 | Week 2 | Week 3 | Week 4 | 6 months after the disease onset |
| Visit | 1 | / | 2 | / | 3 | 4 |
| Enrolment | ||||||
| Eligible screening | ✓ | |||||
| Informed consent | ✓ | |||||
| Basic information | ✓ | |||||
| History of present illness/Past medical history | ✓ | |||||
| Comorbidities/Concomitant medications | ✓ | |||||
| Interventions | ||||||
| Sham EA group (n=37) | ✓ | ✓ | ✓ | ✓ | ||
| Continuous-pulse EA group (n=37) | ✓ | ✓ | ✓ | ✓ | ||
| Intermittent-pulse EA group (n=37) | ✓ | ✓ | ✓ | ✓ | ||
| Assessment | ||||||
| FNGS 2.0 | ✓ | ✓ | ✓ | ✓ | ||
| SBGS | ✓ | ✓ | ✓ | ✓ | ||
| FDI | ✓ | ✓ | ✓ | ✓ | ||
| sEMG | ✓ | ✓ | ✓ | ✓ | ||
| Assessment of patient blinding | ✓ | ✓ | ||||
| Adverse events | ✓ | ✓ | ✓ | ✓ | ✓ | |
FDI, Facial Disability Index; FNGS 2.0, Facial Nerve Grading System 2.0; SBGS, Sunnybrook Grading Scale; sEMG, surface Electromyography.
Primary outcome measure
Change from baseline in the Facial Nerve Grading System 2.0 score. The Facial Nerve Grading System 2.0 (FNGS 2.0) is a clinician-rated scale developed from the original House-Brackmann scale.34 It is widely used to evaluate the severity of facial nerve dysfunction of four regions including brow, eye, nasolabial fold and oral commissure, with a score ranging from 1 to 6 each area. The severity of secondary movement is also assigned a score of 0–3. The total score ranges from 4 to 24 and is categorised into Grade I (normal function) to Grade VI (complete paralysis), with higher scores and grades indicating worse facial nerve dysfunction.
Secondary outcome measure
Change from baseline in the root mean square ratio. The root mean square (RMS) reflects the average amplitude of muscle electrical activity and provides an objective indicator of the extent of motor unit recruitment and rhythmic facial muscle contractions.35 RMS ratio between the affected and unaffected sides (RMS%) can help quantify the degree of recovery and facial symmetry by assessing the facial muscle strength.36
Change from baseline in the median frequency ratio. Median frequency (MDF) is one of the sEMG parameters which has potential value in revealing muscle characteristics, such as fatigue patterns.37 38 In this study, MDF ratio between the affected and unaffected sides (MDF%) will be assessed to evaluate the facial muscle characteristics.36
Change from baseline in the Sunnybrook Grading Scale score. The Sunnybrook Grading Scale (SBGS) is a standardised grading scale assessing resting symmetry, voluntary facial movements and synkinesis.39 Greater severity of facial muscle dysfunction is presented with higher scores in resting symmetry and synkinesis and lower scores in voluntary movement. The integrated score ranges from 0 to 100, with higher scores indicating better facial nerve function. An increase in score over time reflects clinical improvement.
Change from baseline in the Facial Disability Index score. The Facial Disability Index (FDI) includes Facial Disability Index-Physical Function (FDIP) and Facial Disability Index-Social Function (FDIS) subscales and is a patient-reported measure that assesses both the physical and social effects of facial dysfunction.40 The FDIP evaluates the psychological and social functions of patients with Bell’s palsy, including five items scored from 1 to 6. Higher scores reflect more severe impairment of social functioning. The FDIP assesses the daily activities, such as drinking and eating in patients with Bell’s palsy, with five items scores ranging from 0 to 5, respectively. Higher scores indicate a better degree of preserved physical function and reduced difficulty in daily living.
Sample size
The sample size was calculated using PASS V.15.0 (NCSS, LLC, Kaysville, Utah, USA). The primary outcome is the change in FNGS 2.0 score after 4 weeks of treatment. Based on preliminary trial observations and clinical experience, the change in FNGS 2.0 score after 1 month of sham EA for Bell’s palsy was 3.8±1.48, after 1 month of continuous pulse pattern 2 Hz EA was 4.9±1.60 and after 1 month of intermittent pulse pattern 35 Hz EA was 5.4±1.72. Assuming an alpha level of 0.05 and a power of 1−β=0.90, the resulting required sample size was 87 participants. To account for potential dropouts and refusals, an additional 20% was added, resulting in a final required sample size of 111 participants, with at least 37 participants in each group.
Data collection and management
All personal data will be kept confidential and identified by a unique study number in accordance with privacy regulations and institutional requirements throughout the trial. Data will be collected by trained researchers using standardised case report forms. Baseline characteristics, intervention records, outcome measures and adverse events will be recorded according to the study schedule. Completed case report forms will be reviewed for completeness and accuracy and entered into a secure electronic database by authorised researchers. Data quality will be maintained through routine checks for missing, inconsistent or implausible data, with discrepancies resolved against source documents where necessary. Access to the database will be restricted to authorised researchers. Documents containing personal identifiers will be stored separately from the study data in secure, password-protected files.
Adverse events
Adverse events will be carefully monitored and documented throughout the trial. Detailed records will include the time of onset, severity, duration, relationship to the intervention, actions taken and outcomes. The frequency and types of adverse events will be summarised descriptively. If a serious adverse event occurs, appropriate medical management will be provided immediately, and the sponsor and the sponsor’s Institutional Review Board (IRB) will be notified in accordance with applicable requirements. The principal investigator will determine whether the participant should be withdrawn from the study based on the participant’s safety and clinical condition. Participants who experience trial-related adverse events will receive appropriate treatment without bearing the related medical costs.
Monitoring and quality control
Trial conduct will be monitored throughout the study to ensure participant safety, protocol adherence, intervention compliance, data quality and timely reporting of adverse events. The sponsor’s IRB will provide ethical and quality oversight, and annual progress reports will be submitted to the sponsor’s IRB. Before study initiation, all researchers will receive standardised training, and standard operating procedures will be implemented to promote consistency across clinical centres. Case report forms and source documents will be reviewed regularly to ensure the completeness, accuracy and consistency of trial data. The sponsor, principal investigators and study coordination team will oversee trial conduct and implement quality control procedures throughout the study. Given the short study duration of 1 month, no formal interim analysis is planned. The decision to terminate the trial may be made by the sponsor after review or recommendation by the sponsor’s IRB.
Statistical analysis
Data from all randomised participants will be analysed using SPSS V.29.0 (IBM, Armonk, New York, USA). For continuous variables, normality will be assessed. Normally distributed data will be presented as means and SD; otherwise, data will be reported as medians, first quartiles and third quartiles. Categorical and ordinal variables will be presented as frequencies and percentages. Baseline characteristics between groups will be compared.
Efficacy will be evaluated using both the ITT and PP analysis sets. The ITT analysis will be considered the primary analysis, and the PP analysis will be performed as a supplementary sensitivity analysis to assess the robustness of the findings. FNGS 2.0, SBGS and FDI scores will be analysed as continuous variables. RMS% and MDF% derived from sEMG will also be analysed as continuous variables. Because outcomes are repeatedly measured in three parallel treatment groups, longitudinal between-group differences will be evaluated using linear mixed-effects models (LMMs). For each outcome, the post-baseline measurements obtained at week 2, week 4 and 6 months after the disease onset will be included as dependent variables. Treatment group, assessment time and the treatment-group-by-time interaction will be included as fixed effects, and the corresponding baseline value measured at day 0 will be included as a covariate. A participant-specific random intercept will be included to account for within-participant correlation. Assessment time will be modelled as a categorical variable.
For the primary outcome, week 4 will be considered the primary efficacy assessment time point. An overall omnibus test comparing the three treatment groups will first be performed using LMM. If the overall group difference at the primary assessment time point is statistically significant at a two-sided α level of 0.05, prespecified pairwise contrasts based on estimated marginal means will be conducted for the following comparisons: (1) continuous-pulse EA versus sham EA, (2) intermittent-pulse EA versus sham EA and (3) continuous-pulse EA versus intermittent-pulse EA. The Holm procedure will be applied to adjust for the three pairwise comparisons and control the family-wise type I error rate. Adjusted mean differences, 95% CIs and multiplicity-adjusted p values will be reported.
The treatment-group-by-time interaction will also be examined to assess whether longitudinal changes differ among the three groups. Between-group comparisons at week 2 and 6 months after the disease onset will be considered secondary longitudinal analyses and will be estimated from the same mixed-effects model. The same general LMM framework will be applied to the secondary outcomes, including SBGS score, FDI score, RMS% and MDF%. Model residuals will be assessed to evaluate the distributional assumptions. If substantial skewness is observed for the electromyographic ratio variables, an appropriate transformation, such as logarithmic transformation, will be considered and the corresponding analysis will be reported.
Under the missing-at-random assumption, the primary LMM analysis will use all available longitudinal observations through likelihood-based estimation without single-value imputation. Multiple imputation will be performed as a sensitivity analysis for missing outcome data. The imputation model will include randomised treatment group, assessment time, baseline outcome values, available repeated outcome measurements and relevant baseline variables associated with the outcome or missingness. Each imputed dataset will be analysed using the same prespecified LMM, and estimates and standard errors will be combined according to Rubin’s rules. The robustness of the results from the primary analysis will be assessed by comparison with those obtained from the multiple-imputation analysis.
Ethics and dissemination
This trial will be conducted in accordance with the ethical guidelines of the Declaration of Helsinki. This trial has been approved by the Ethics Committee of The First Affiliated Hospital of Zhejiang Chinese Medical University (2025-KL-067-01) and the Ethics Committee of The Third Affiliated Hospital of Zhejiang Chinese Medical University (ZSLL-KY-2025-134). Written informed consent will be obtained from all participants before enrolment. Any substantive amendments to the study protocol will be submitted to the Ethics Committees of both participating centres for review and approval, and relevant changes will be updated in the trial registry as appropriate.
The findings of this study will be disseminated through publication in peer-reviewed journals and presentation at relevant scientific conferences. Trial results will also be reported on ClinicalTrials.gov, as applicable. Individual participant data (IPD) collected during this trial will not be shared with other researchers.
Patient and public involvement
Patients and/or the public were not involved in the design, or conduct, or reporting, or dissemination plans of this research.
Study status
The clinical trial is currently not yet recruiting. The first participant is expected to be enrolled in September 2026, and the last visit of the last participant is anticipated to be completed in October 2027.
Discussion
In clinical studies of Bell’s palsy, rater-based scales are commonly used as the primary assessment methods because they are convenient and easy to administer.41 42 However, conventional Bell’s palsy grading scales have several recognised limitations, including subjective scoring, limited regional precision and relatively insufficient sensitivity to subtle changes.43 In this study, sEMG will be used in addition to clinical scales as an objective tool for evaluating the symptom severity and treatment outcomes in Bell’s palsy. Among various neuromuscular electrophysiological assessment methods, sEMG has several advantages, including its noninvasive nature, absence of pain, and ability to detect subtle muscle activity.43 44 Notably, sEMG has been used to characterise facial muscle electromyographic features in Bell’s palsy.45–48 For example, a study comparing sEMG characteristics between healthy participants and patients with Bell’s palsy found that muscle activation patterns during tasks were nearly symmetrical in healthy participants but asymmetric in patients with Bell’s palsy.49 Additionally, sEMG has also been used to assess the abnormal muscle activation associated with synkinesis, which is characterised by the involuntary activation of muscles beyond the primary movement region.50 Regarding specific sEMG indicators, RMS is widely used and is associated with neural excitation and muscle strength.51 RMS values from recruited muscles reflect average muscle strength throughout the muscle contraction.52 In addition to RMS, this study will include MDF as a secondary sEMG indicator because MDF has been used to assess muscle endurance in previous studies.45 53 Therefore, using sEMG as an objective assessment tool in this study provides a feasible approach for further characterising muscle activation during recovery from Bell’s palsy.46
This study will focus on the effects of EA in the patients with Bell’s palsy and aims to more rigorously evaluate the efficacy of this increasingly recognised therapy. Although multiple studies have shown that EA may promote nerve regeneration and support nerve repair and recovery,47 48 54 existing studies of EA for Bell’s palsy have generally lacked a design of sham EA control group, making it difficult to distinguish the specific therapeutic effects from placebo effects. Therefore, this study includes a sham EA group to improve methodological rigour and strengthen the interpretability of the findings in patients with Bell’s palsy.
However, this has several limitations. First, because of limited funding, the treatment period will be restricted to 4 weeks, which may be insufficient for many patients with severe Bell’s palsy. Second, participants with Bell’s palsy will be recruited from only two hospitals in Hangzhou, China, which may limit the generalisability of the findings to other regions. Future studies should recruit participants from different regions to further validate the findings.
Supplementary material
Acknowledgements
The authors would like to express their gratitude to the participants who will be involved in this trial.
Footnotes
Funding: This trial was financially supported by the Youth Talent Supporting Program of Zhejiang Provincial Traditional Chinese Medicine Science and Technology Program, administered by the Administration of Traditional Chinese Medicine of Zhejiang Province(2025ZR110). The funder has no role in designing and analyzing of this study.
Prepublication history and additional supplemental material for this paper are available online. To view these files, please visit the journal online (https://doi.org/10.1136/bmjopen-2026-122378).
Provenance and peer review: Not commissioned; externally peer reviewed.
Patient consent for publication: Not applicable.
Patient and public involvement: Patients and/or the public were not involved in the design, or conduct, or reporting, or dissemination plans of this research.
Data availability statement
No data are available.
References
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