Effective and cost-efficient treatment approaches are crucial in healthcare to optimize patient outcomes. This study evaluates and compares the clinical outcomes and cost-effectiveness of Korean and Western medicine collaborative treatment (CT) with usual care (UC) for patients with facial palsy (FP).

A two-arm comparative, multicenter, prospective, observational study was conducted at 11 nationwide hospitals participating in the fourth phase of the national pilot project for CT. A total of 130 FP patients were enrolled at baseline, with follow-up assessments at 4 weeks and 12 weeks post-baseline. Clinical outcomes were evaluated using the House-Brackmann Grading Scale (HBGS), Numeric Rating Scale (NRS), EuroQol-5 Dimensions (EQ-5D-5L), and EuroQol-Visual Analogue Scale (EQ-VAS) at all three time points of the study. The cost-effectiveness evaluation was assessed using Cost per QALYs (Quality-Adjusted Life Years), Incremental Cost-Effectiveness Ratio (ICER), and Net Monetary Benefit (NMB).

The mean HBGS, NRS and EQ-VAS scores significantly improved in both groups over time (each, p < 0.05). Compared to UC, CT demonstrated significantly higher EQ-5D-5L scores (0.94 ± 0.11 vs. 0.91 ± 0.13), and this effect remained significant even after adjusting for age, sex, duration, and income level (β = 0.06, p < 0.05). From a limited societal perspective, the total cost difference between the two groups was not statistically significant; however, the QALYs gained were significantly higher in patients who received CT than those who received UC (0.010 QALYs vs. 0.008 QALYs). The ICER for CT was estimated at 28.1 million Korean Won (KRW) per QALY. The probability that CT would be more cost-effective than UC exceeded 50% at a WTP threshold of 30.5 million KRW per QALY.

Our study highlights that CT enhances a better quality of life and is more cost-effective for FP treatment, suggesting it is a valuable alternative to usual care. Further large-scale clinical trials and cost-effectiveness studies are warranted to explore its broader application and validate these findings.

The study design was registered with the Clinical Research Information Service (CRIS) of South Korea at https://cris.nih.go.kr/ (KCT0007682) on September 07, 2022.

Facial palsy (FP) refers to impaired facial movements caused by nerve damage, which can manifest on one or both sides of the face [1]. Affecting approximately 15–40 per 100,000 adults annually [2], FP is a notably common condition, often presenting as sudden-onset unilateral facial paralysis. It is estimated that 29% of FP patients experience long-term complications, including facial asymmetry and synkinesis [3, 4]. Since facial expressions are crucial for interpersonal communication and self-image, FP can significantly diminish quality of life and impose considerable emotional burdens [5]. Despite treatment advances, a significant number of FP patients continue to experience incomplete recovery, potential side effects, and limited efficacy, prompting the exploration of additional therapeutic options [6, 7]. This highlights an increasing need for more treatment options to enhance the overall well-being of FP patients [3].

South Korea, with its unique dichotomized healthcare system that integrates both Korean Medicine (KM) and Western Medicine (WM), provides a distinctive environment for treating FP [4]. KM practices such as acupuncture, moxibustion, and herbal medicine are often used alongside WM treatments to enhance patient outcomes [8, 9]. In 2019, 111,089 patients sought treatment for facial nerve disorders in Korea, making it the most common condition treated in KM hospitals and clinics [10]. FP ranks sixth among frequently treated conditions in outpatient care and tenth in inpatient care for collaborative treatment [4]. Prior studies have explored the efficacy of acupuncture and herbal medicine for FP, with positive patient satisfaction and improvements in recovery and quality of life [3, 5, 6, 10,11,12]. However, with the increasing use of both medical systems and the constraining coverage of national health insurance, there has been increasing demand for research on the cost-effectiveness and broader economic implications of these collaborative treatments in real-world settings [3, 13]. To address these aspects and smooth institutional implementation of KM-WM collaborative treatment (CT), the South Korean government initiated a national pilot project for CT in 2016 [14]. The first phase identified that collaborative treatment was frequently practiced for musculoskeletal pain, FP, and stroke. In the second phase, collaboration fees were introduced for standard procedures for four major severe diseases. The third phase, which commenced in October 2019, maintained this structure while adding a quality-based differential fee model. By 2022, the fourth phase expanded to 75 institutions to systematize CT and enhance effectiveness research [12, 14].

FP has significant socioeconomic and psychological consequences for patients. Those affected often experience social isolation and decreased confidence, leading to a chain of mental health issues that further increase healthcare utilization and societal costs [5, 10]. A study reported that over 31% of FP patients exhibited significant levels of depression and anxiety [15]. The economic burden of FP extends beyond direct medical costs to include indirect costs such as lost productivity. Therefore, by evaluating treatment outcomes and associated costs, this study aims to address these gaps by providing valuable insights for the effective management of FP. Exploring these aspects will be crucial to determine whether collaborative approaches offer not only clinical benefits but also financial advantages [16]. Along with the fourth phase of the national pilot project for CT, we conducted a prospective observational analysis of the Registry for KM and WM Collaborative Treatment (REKOMENT) to assess and compare the clinical outcomes and cost-effectiveness (utility) of CT with usual care (UC) for FP patients. Our findings may provide significant implications for decision-makers in implementing the CT protocol for FP patients under South Korea’s national health insurance (NHI) coverage.

This two-arm comparative, multicenter, prospective, observational study was designed to evaluate and compare the clinical and cost-effectiveness of CT with UC alone for FP patients. Patients were enrolled at 11 nationwide hospitals participating in the fourth phase of the national pilot project for CT. FP was systematically classified using the International Classification of Diseases (ICD-10): G51.0 (Bell’s palsy), G51.8 (other disorders of facial nerve), and G51.9 (disorder of facial nerve, unspecified). The study was conducted during the fourth phase of the national CT pilot project from January 26, 2023, to December 19, 2023. The study design was registered with the Clinical Research Information Service (CRIS) of South Korea at https://cris.nih.go.kr/ (KCT0007682) on September 07, 2022 [17]. The study adhered to STROBE, CONSORT, and CHEERS guidelines (Additional Files 1, 2, and 3). Furthermore, the study followed the principles outlined in the Declaration of Helsinki and the Good Research Practices recommended by the International Society for Pharmacoeconomics and Outcomes Research (ISPOR) [18]. Ethical approval was obtained from the ethical review board of all the following institutions: Mokpo Dongshin University Korean Oriental Hospital (DSMOH-22-04), Daegu Hanny University Hospital (DHUMC-D-22009-AMD-03), Dongguk University Ilsan Oriental Hospital (DHIOH-2022-07-001-004), Kyung Hee University Korean Medicine Hospital (KOMCIRB-2020-03-003-007), Wonkwang University Jeonju Oriental Medicine Hospital (WUJKMH-IRB-2022-007), Chenonan Dosol Korean Oriental Hospital (P01-202011-21-011), Bucheon Jaseng Korean Medicine Hospital (JASENG 2022-08-013-007), Samse Korean Oriental Medical Hospital (P01-202011-21-011), Dong-Eui University Korean Medicine Hospital (DH-2022-10), Woosuk University Jeonju Oriental Medicine Hospital (WSOH-IRB-H2207-03-03), and Kkotdam Hospital of Korean Medicine (P01-202011-21-011). Written informed consent was obtained from all participants.

FP patients were enrolled at the study’s baseline (the first day of a hospital visit), with follow-up assessments at 4 weeks and 12 weeks post-baseline. The study included patients over 19 years old who visited the participating institutions for the first time and provided written informed consent. Exclusion criteria included difficulties with follow-up, challenges in understanding and responding to research questionnaires, and participation in other clinical studies. As mentioned above, due to the observational nature of the study, investigators from participating institutions and the subjects were not blinded at baseline. However, follow-up assessments and analysis were conducted with blinding at a separate monitoring center, and the process of identifying allocated groups using electronic medical records after the final follow-up was also blinded.

UC refers to the treatment provided exclusively with either KM or WM, whereas CT refers to treatment with both KM and WM. UC with KM included acupuncture, herbal formulations, pharmacopuncture, and physiotherapeutic therapy [19], whereas WM included corticosteroids during the acute phase [20]. Participants who received CT were assigned to the CT group, and those who received UC were assigned to the UC group for the analysis. The detailed intervention protocols for CT and UC in this nationwide pilot project were defined as critical pathways (CP), supported by clinical evidence, methods, and recommendations in the clinical practice guideline (CPG) [19] (Additional File 4).

Participants’ information was collected at each study time point: baseline, 4 weeks, and 12 weeks. Baseline data, including socio-economic and disease-related variables, were collected during the initial visit, whereas clinical and cost-effectiveness indicators were assessed at each time point. Trained and experienced researchers from each institution collected the information using a semi-structured questionnaire, which included clinical and economic case report forms. This questionnaire was developed based on a literature review [3, 4, 10, 21, 22] and in-depth discussions with researchers, clinical professors, and experts from the participating institutions (Additional File 5). Face-to-face interviews were conducted and lasted approximately 15–20 min. We incorporated baseline covariates, including age, gender, monthly income, duration between onset to first hospital visit, and medical utilization and costs before enrollment in the study.

Cost data were captured using an economic case report form (eCRF) that included direct medical costs, direct non-medical costs, and productivity losses. Direct medical costs from study hospitals were obtained from administrative data, while costs from other hospitals, such as public hospitals, health centers/clinics, and pharmacies, were captured through the eCRF. The study hospital costs were the costs paid (or reimbursed) by participants (and NHI) for their treatment of the study disease during the study period. Direct non-medical costs, such as travel costs and time costs for a hospital visit, were estimated by multiplying hospital visit frequencies by unit travel costs and hourly wages. Productivity loss was calculated based on absenteeism, and presenteeism was not measured to avoid double counting, as the utility measure was already affected by disease status. Since there are no clear guidelines and reasonable friction cost methods for calculating productivity loss in Korea, we used the human capital approach estimation method in this study by simply summing the costs incurred by absenteeism (number of days of absence × cost per day) [9]. As the study’s follow-up period did not exceed one year, discount rates for time preferences were not applied to costs and utility outcomes. The unit costs and sources related to direct medical and non-medical costs and productivity losses are provided in Table 1. All cost items in this study were converted to 2024 values using the following formula based on South Korea’s annual Consumer Price Index (CPI) [23]:

Converted cost = Captured cost × (CPI of 2024 / CPI of the cost capture year)

The effectiveness of the treatment on FP was evaluated using the House-Brackmann Grading Scale (HBGS), Numeric Rating Scale (NRS), EuroQol-5 Dimensions (EQ-5D-5L), and EuroQol-Visual Analogue Scale (EQ-VAS) at all three time points of the study (at baseline, 4 weeks, and 12 weeks). The HBGS is a validated tool for assessing the severity of facial nerve dysfunction, classifying FP into six grades, from normal function (Grade I) to total paralysis (Grade VI) [24, 25]. Each patient was evaluated and assigned a grade based on facial movement and symmetry. Overall pain intensity and discomfort associated with FP were measured using NRS, where patient rated their pain on a scale from 0 (no pain) to 10 (worst pain imaginable) [26, 27]. The Korean version of EQ-5D-5L was utilized to measure health-related quality of life, focusing on five dimensions: mobility, self-care, usual activities, pain/discomfort, and anxiety/depression, with each dimension rated on five levels of severity, from no problems to extreme problems [5, 28]. An increase in EQ-5D scores indicates an improvement in the patient’s overall health-related quality of life. The patient’s self-rated overall health level was assessed using EQ-VAS on a scale of 0-100 [29, 30]. Higher EQ-VAS scores reflect better perceived health status.

Baseline characteristics of the participants were presented using descriptive statistics, including frequencies, percentages, and mean (standard deviation). The normality of the data was assessed using the Shapiro-Wilk test and Q-Q plots. Categorical and continuous variables were analyzed using the Chi-square test and Student’s t-test, respectively. The Mann-Whitney U-test and Kruskal-Wallis test were employed when the assumptions of equal variances and normality were violated.

The clinical and cost-effectiveness were assessed using ITT data, with parameter estimates derived based on Rubin’s rule [31]. To establish the ITT dataset, the patterns and proportions of missing data were identified, and the mechanism of missingness, along with the imputation model, was determined using Little’s test. The total proportion of missing data was 5% (missing participant, 9%), and the mechanism was found to be missing completely at random (MCAR, Chi-square distance = 5.09, p-value = 0.28) (Table 2). Ten imputed datasets were created using multiple imputations, employing a chained equation approach with predictive mean matching based on a K-nearest neighbor algorithm with five neighbors, and the imputed missing values were utility scores of EQ-5D-5L, direct medical costs, direct non-medical costs, and productivity costs for each visit. Upon verifying the covariate associations of the baseline variables, we observed an estimated covariance-dependent missing completely at random mechanism (MCAR-CDM). The MCAR-CDM refers to a situation where the probability of missingness depends on external covariates but remains independent of the observed and unobserved data values [32]. This differs from traditional MCAR, where missingness is entirely random and unrelated to any variables. While MCAR assumes no relationship between missingness and data, MCAR-CDM allows for missingness influenced by external covariates without biasing inference, as long as the external covariates are accounted for [32].

To analyze the clinical effectiveness and the between-group differences at each time point, repeated measures analysis of variance (ANOVA) and a generalized linear mixed model (GLMM) adjusted for covariates were employed. All statistical analyses were performed using Stata MP (Version 14.0). The significance level was set at p-value < 0.05.

The economic evaluation of the treatment was evaluated using cost-utility analysis, including several economic evaluation metrics: Cost per QALYs (Quality-Adjusted Life Years), Incremental Cost-Effectiveness Ratio (ICER), Net Monetary Benefit (NMB), and Cost-Effectiveness Acceptability Curve (CEAC) [9, 16]. Quality of life was measured using the EQ-5D-5L utilities with the South Korean national tariff [33, 34] and the area under the curve method [35]. ICER was determined by dividing the incremental costs by the incremental QALYs gained [36]. The analysis perspective is a limited societal, similar to a healthcare payer perspective, which is recommended as the reference case analysis for health insurance registration in South Korea [37]. When estimating the cost-effectiveness probability of ICER, we used a threshold of 30,500,000 KRW per QALY, as recommended by Korea’s National Evidence-based Healthcare Collaborating Agency (NECA), which reflects the national norms [38, 39] and is also based on the 2023 gross domestic product (GDP) per capita (USD 33,745) [40, 41]. The probability of the collaborative treatment being cost-effective was measured based on changes in the willingness to pay (WTP) for health outcomes [34]. The NMB was calculated using the following equation:

NMB = incremental effectiveness (QALYs) × WTP – cost differences.

Analyses for ICER were performed using both intention-to-treat (ITT) and per-protocol (PP) data from a limited societal perspective (LSP) and societal perspective (SP), displaying the cost-effective probability based on the proposed WTP threshold (KRW/QALY). To address the sampling uncertainty of the ICER’s point estimates, 95% confidence intervals (CIs) were calculated using the bootstrapping method (1,000 iterations) and a seemingly unrelated regression model. Additionally, the probabilities of each alternative being cost-effective according to the changes in the national willingness to pay were presented using the CEAC.

A total of 130 FP patients were enrolled in the study and included in the ITT analysis. The CT group consisted of 85 patients, whereas the UC group comprised 45 patients. Out of 130 participants, 118 patients were included in the PP analysis. Twelve patients (three from the UC and nine from the CT group) who failed to complete the follow-ups were excluded. The study process is detailed in Fig. 1.

Study process and flow chart. Collaborative treatment refers to treatment that includes both Korean and Western medicine. Usual care refers to treatment exclusively with either Korean medicine or Western medicine. ITT, intention-to-treat; PP, per-protocol; n, number

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Table 3 presents the baseline information of the participants according to the treatment group. The mean age of the participants was 48.49 ± 15.98 years in the UC group and 52.19 ± 14.81 years in the CT group. There were no significant differences between the UC and CT groups according to age, sex, monthly income, duration, HBGS, NRS, EQ-5D-5L, and EQ-VAS assessments (each, p > 0.05).

The mean changes in clinical outcomes across study time points for both treatment groups, analyzed using repeated measures ANOVA with PP data, are shown in Table 4; Fig. 2. FP severity and dysfunction based on HBGS significantly decreased over time in both groups. The UC group’s mean HBGS score decreased from 3.40 ± 1.10 at baseline to 1.83 ± 0.85 at 12 weeks, whereas the CT group showed a reduction from 3.28 ± 0.92 to 1.46 ± 0.70. However, there were no significant between-group differences (p = 0.366) (Fig. 2A). Similarly, pain levels, assessed using the NRS, showed a significant reduction over time in both groups. In the UC group, the mean NRS score decreased from 5.29 ± 2.50 at baseline to 0.33 ± 1.10 at 12 weeks. The CT group exhibited a significant reduction from 4.79 ± 2.18 at baseline to 0.26 ± 0.79 at 12 weeks. However, there were no significant differences in changes over time between the groups (Fig. 2B).

Mean variations in clinical outcomes during the observation period. (A) HBGS, House-Brackmann grading scale; (B) NRS, numeric rating scale; (C) EQ-5D-5L, EuroQol-5 dimensions; (D) EQ-VAS, EuroQol-visual analogue scale

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The EQ-5D-5L scores, reflecting quality of life, improved significantly in both groups. In the UC group, the mean EQ-5D-5L score increased from 0.85 ± 0.11 at baseline to 0.91 ± 0.13 at 12 weeks, whereas the CT group exhibited an increase from 0.81 ± 0.12 to 0.94 ± 0.11. Significant within-group (p < 0.001) and between-group (p = 0.044) effects were observed, indicating that the CT group showed greater improvements in overall quality of life compared to the UC group (Fig. 2C). The EQ-VAS scores showed consistent improvement in both groups over time. The mean EQ-VAS score in the UC group increased from 64.42 ± 16.57 at baseline to 76.28 ± 17.46 at 12 weeks, whereas in the CT group, it increased from 60.66 ± 21.76 to 79.34 ± 18.02. Although the interaction between the group and time did not reach statistical significance, a meaningful difference was observed between the two groups (p = 0.074) (Fig. 2D).

We further analyzed the clinical effectiveness of both treatments across study time points using a GLMM analysis with ITT data, as depicted in Table 5. After adjusting for confounding variables, the EQ-5D-5L showed statistically significant differences between the two groups at 12 weeks (β = 0.06, p = 0.046) and marginal significance at 4 weeks (β = 0.05, p = 0.072). The EQ-VAS demonstrated significance at 4 weeks (β = 8.04, p = 0.041) and marginal significance at 12 weeks (β = 6.56, p = 0.091).

Table 1 presents the total costs and QALYs for 3 months according to the treatment group. The mean differences in total costs between the UC and CT groups based on LSP and SP were KRW 250,572 (LSP: UC = KRW 3,844,052 ± 3,580,168; CT = KRW 4,094,624 ± 3,177,720) and KRW 651,683 (SP: UC = KRW 6,607,064 ± 5,283,559; CT = KRW 7,258,747 ± 5,380,638), respectively. The QALYs gained during the study period were significantly higher in patients who received CT than those who received UC (p = 0.031).

The results of the cost-effectiveness analysis, including ICER, NMB, and CEAC, are shown in Table 6; Figs. 3 and 4. The CT group demonstrated greater quality of life and health benefits than the UC group (0.010 QALYs vs. 0.008 QALYs) at a total mean cost of KRW 279,984 in the bootstrapping model based on ITT analysis. The regression models in sensitivity analysis estimated that the ICER based on mean values was lower than the proposed WTP threshold of 30,500,000 KRW per QALY. At this WTP threshold (KRW per QALY), the probability that CT was more cost-effective than UC exceeded 50% in both PP and ITT analyses. Additionally, the mean NMB at the WTP threshold of 30.5 million KRW per QALY was 18,488 KRW, with a 51% probability.

Cost-effectiveness analysis of the treatment according to intention-to-treat (ITT) and per-protocol (PP) analysis. Values were calculated using 95% CI bootstrapping (1,000 iterations) for the incremental cost-effectiveness ratio (ICER) and the 95% CI for net monetary benefit (NMB) according to variations in the national threshold. WTP, willingness to pay (KRW/QALY); cost in Korean won (KRW)

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Cost-effectiveness acceptability curve (CEAC) of collaborative treatment. QALY, quality-adjusted life years; KRW, Korean won

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To the best of our knowledge, this is the first study to explore and compare the clinical and cost-effectiveness of CT with UC alone for FP patients in the fourth phase of the national pilot project for CT. Our findings demonstrated that CT significantly improves the health-related quality of life compared to UC alone. Additionally, CT showed greater cost-utility gains based on QALYs, indicating that CT not only enhances clinical outcomes but also offers a sustainable economic alternative for FP treatment.

The importance of clinical and cost-effectiveness evidence in healthcare cannot be overstated. Policymakers require robust data to allocate resources efficiently and design health interventions that yield the best outcomes for patients [4, 42]. The findings from this study reinforce the need for evidence-based healthcare practices, demonstrating that CT offers substantial benefits over UC alone. This aligns with similar findings in other studies that emphasize the value of integrating various treatment modalities, thereby optimizing patient care and enhancing quality of life [13, 43]. Moreover, cost-effectiveness evidence is critical for supporting the inclusion of novel treatments in national healthcare systems, thereby making them accessible to a wider population [4, 6, 44]. An increasing body of literature assesses the efficacy and economic evaluation of complementary and alternative medicine (CAM) globally [6, 9, 21, 22, 45]. Studies conducted in South Korea and Europe have shown that acupuncture significantly alleviates pain in patients with low back pain and neurological disorders, demonstrating its potential as an alternative treatment [9, 22, 46]. Additionally, CAM therapies, such as herbal medicine and acupuncture, often result in cost savings and improved clinical outcomes for chronic conditions [13, 34]. These highlight the global trend of integrating CAM into conventional healthcare systems and influencing healthcare decisions to support such collaboration [47, 48].

Several studies have reported the clinical effectiveness of CT for FP [6, 49, 50]. A randomized controlled trial showed CT combined with steroids was more effective in treating FP [51]. Studies from Turkey and China reported a significant reduction in HBGS scores in FP patients treated with acupuncture [52], as well as improvements in disability and quality of life [53]. A study in South Korea observed a significant onset of FP after 2 (OR, 1.47) and 3 months (OR, 2.05) of treatment based on the HBGS index [6]. The increasing use of CT for FP in South Korea indicates a rising patient preference for CT. FP patients treated with CT reported higher satisfaction with the treatment and recognized it as a primary treatment for FP [54]. A study by Ga Young et al. showed that FP treatment over 6 months significantly improved both HBGS (5 to 3) and NRS (10 to 2.5) scores [55]. Furthermore, over 85% of the patients treated with CT fully recovered within 2 months [56]. These findings align with our study, demonstrating that CT for FP has a substantial and greater impact on clinical outcomes than UC. Although the economic evaluation of CT for FP is critical for assessing its overall effectiveness, this area remains underexplored in South Korea. This gap is one of the major strengths of our study. However, some studies in South Korea and abroad have demonstrated that CT is significantly cost-effective in treating low back pain and osteoarthritis compared to UC [9, 34, 57]. A study in the UK assessed the economic evaluation of steroids for FP and showed a 77% probability of cost-effectiveness at £30,000 [58]. In our study, CT demonstrated greater cost-effectiveness than UC alone for FP treatment, with a 55% probability of willingness to pay at the WTP threshold level of 30,500,000 KRW per QALY. The cost-effectiveness of CT for FP may be influenced by multiple factors, including variations in treatment protocols, differences in healthcare systems, and patient adherence. Additionally, long-term cost benefits should be explored, as effective FP management through CT may reduce the need for repeated interventions and additional healthcare expenses. Therefore, further studies should incorporate large-scale real-world data on costs and utilities to enhance the generalizability and robustness of economic evaluations.

The CT pilot project is a groundbreaking initiative aimed at fostering effective collaboration of KM and WM for the treatment of diverse health conditions, including FP, in South Korea. This collaboration is essential in meeting the growing demand for holistic and comprehensive healthcare solutions. By leveraging the strengths of both KM and WM, the pilot project could serve as a model for other countries, demonstrating how CAM and modern medical practices can work synergistically to improve patient care [12, 14, 59]. Such collaboration reflects a broader recognition of diverse treatment modalities, aligning with the World Health Organization’s recommendations on incorporating collaborative medicine into national health systems [60, 61]. Our study has significant scientific implications, particularly for the fields of collaborative medicine and health economics. Given the scarcity of studies investigating the clinical and cost-effectiveness of CT for FP, this research contributes to the growing discourse and clinical guidelines on the collaboration of KM and WM in South Korea [3]. It paves the way for further studies exploring similar collaborative approaches for other medical conditions, enhancing our understanding of the potential benefits and cost savings associated with collaborative care [62]. Therefore, the positive outcomes observed in this study could benefit future research investigating the mechanisms by which CT leads to improved patient outcomes across various healthcare conditions, including FP.

Although our study provides valuable insights, several limitations must be acknowledged. First, this was an observational study rather than a randomized controlled trial, which may limit the definitive conclusions about cost-effectiveness. However, it is important to note that observational studies still play a critical role in real-world evidence generation, especially in contexts where experimental studies are challenging to conduct due to logistical, ethical, or economic reasons. This study represents a significant milestone as the first-ever study in Korea to assess the comparative cost-effectiveness of CT for FP and provides an essential baseline foundation and valuable insights into collaborative treatment approaches for FP. Second, despite adjusting for covariates such as age, gender, income, and duration between onset to first visit, and addressing missing data mechanisms, certain biases—such as sample selection and measurement error—may not have been fully mitigated, potentially limiting the generalizability of the findings. Third, although this was a multicenter prospective study, the sample size was not large enough to comprehensively investigate clinical outcomes and cost-effectiveness with adequate statistical power. Fourth, although the study protocol was not published, the study design was properly registered with CRIS. Lastly, it is widely acknowledged that cost utilization surveys may introduce recall bias. Despite these limitations, our findings highlight the potential effectiveness of CT for FP treatment and areas for future research. These findings help bridge the existing evidence gap in CT effectiveness for FP and underscore the importance of collaborative healthcare models. We believe that our study stimulates further investigation, particularly through long-term, large-scale randomized controlled trials and a more diverse demographic representation, which can provide more robust and generalizable conclusions, particularly in terms of cost-effectiveness [9].

CT:

Collaborative treatment

UC:

Usual care

FP:

Facial palsy

HBGS:

House-Brackmann Grading Scale

NRS:

Numeric Rating Scale

EQ-5D-5L:

EuroQol-5 Dimensions

EQ-VAS:

EuroQol-Visual Analogue Scale

QALYs:

Quality-Adjusted Life Years

ICER:

Incremental Cost-Effectiveness Ratio

CEAC:

Cost-Effectiveness Acceptability Curve

NMB:

Net Monetary Benefit

WTP:

Willingness to pay

ITT:

Intention-to-treat

PP:

Per-protocol

LSP:

Limited societal perspective

SP:

Societal perspective

MCAR:

Missing completely at random mechanism

CRIS:

Clinical Research Information Service

NHI:

National Health Insurance

KM:

Korean medicine

WM:

Western medicine

REKOMENT:

Registry for KM and WM Collaborative Treatment

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Conceptualization, Methodology: NamKwen Kim. Acquisition, Data curation, Editing, Investigation: NamKwen Kim, Linae Kim. Writing- original draft: Shiva Raj Acharya, NamKwen Kim. Writing-critical review: NamKwen Kim, Linae Kim, Shiva Raj Acharya,. Statistical analysis: NamKwen Kim, Shiva Raj Acharya. Supervision: NamKwen Kim.

Correspondence to NamKwen Kim.

The study adhered to the principles outlined in the Declaration of Helsinki and the Good Research Practices recommended by the International Society for Pharmacoeconomics and Outcomes Research (ISPOR) [18]. The study design was registered with the Clinical Research Information Service (CRIS) of South Korea at https://cris.nih.go.kr/ (KCT0007682) on September 07, 2022 [17]. The study adhered to STROBE, CONSORT, and CHEERS guidelines (Additional Files 1, 2, and 3). Ethical approval was obtained from the ethical review board of all the following institutions: Mokpo Dongshin University Korean Oriental Hospital (DSMOH-22-04), Daegu Hanny University Hospital (DHUMC-D-22009-AMD-03), Dongguk University Ilsan Oriental Hospital (DHIOH-2022-07-001-004), Kyung Hee University Korean Medicine Hospital (KOMCIRB-2020-03-003-007), Wonkwang University Jeonju Oriental Medicine Hospital (WUJKMH-IRB-2022-007), Chenonan Dosol Korean Oriental Hospital (P01-202011-21-011), Bucheon Jaseng Korean Medicine Hospital (JASENG 2022-08-013-007), Samse Korean Oriental Medical Hospital (P01-202011-21-011), Dong-Eui University Korean Medicine Hospital (DH-2022-10), Woosuk University Jeonju Oriental Medicine Hospital (WSOH-IRB-H2207-03-03), and Kkotdam Hospital of Korean Medicine (P01-202011-21-011). Written informed consent was obtained from all participants.

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