Knowledge Mapping of Acupuncture for Fibromyalgia from 1990 to 2022: A Bibliometric Analysis

Introduction

Fibromyalgia is a disorder characterized by chronic generalized musculoskeletal pain, often accompanied by fatigue, sleep disturbance, anxiety, depression and balance disorder.^1,2 Its prevalence in the general population is 2–8%, and it is the third most common musculoskeletal-related disorder after lumbar pain and osteoarthritis.^3–6 Although the American College of Rheumatology (ACR) issued the first diagnostic criteria for fibromyalgia in 1990,⁷ the clinical diagnosis and treatment of fibromyalgia still face enormous challenges. For example, fibromyalgia is mainly diagnosed based on clinical symptoms, with no specific laboratory indicators and imaging examinations, and prior to revision of the diagnostic criteria for fibromyalgia by the ACR in 2016,⁸ fibromyalgia was mostly considered to be an exclusive diagnosis. Moreover, the accompanying symptoms of fibromyalgia, such as fatigue, sleep disturbance, anxiety and depression, are often misdiagnosed by clinicians as neurological and psychiatric disorders.⁹ Difficulties in diagnosis may prevent patients with fibromyalgia from receiving timely and effective treatment. In addition, fibromyalgia is not sensitive to hormonal drugs and NSAIDs commonly used in rheumatism. The European League Against Rheumatism (EULAR) suggested that non-pharmacological approaches should be first-line treatments for fibromyalgia.¹⁰ Exercise is the only treatment modality with strong recommendations from the EULAR, but is a significant challenge for patients, who find exercise programs difficult to start and maintain, and are concerned that exercise will worsen their pain and fatigue.¹⁰ Therefore, it is necessary to find effective complementary and alternative medicine therapies.

Studies have shown that fibromyalgia is one of the dominant diseases of acupuncture.¹¹ Acupuncture has a good analgesic effect on fibromyalgia, and can effectively relieve the accompanying symptoms such as fatigue, sleep disturbance, anxiety and depression in patients with fibromyalgia.^12,13 However, there is still a lack of bibliometric studies on the cooperation, development trends and research fronts in the field of acupuncture for fibromyalgia.

Bibliometrics is an interdisciplinary subject that applies mathematical and statistical methods to qualitative and quantitative analysis of publications.^14,15 Currently, the most commonly used bibliometric tools are CiteSpace and VOSviewer, since CiteSpace allows effective co-citation analysis, while VOSviewer is user-friendly and has a clear and concise map. The Web of Science Core Collection Database is the most commonly used database for bibliometric analysis, providing references that meet the formatting requirement of CiteSpace-specified reference co-citation analysis.

Therefore, the study used CiteSpace and VOSviewer to perform a visual analysis of publications on acupuncture for fibromyalgia in the Web of Science Core Collection Database, with the aim of understanding the collaboration between research institutions and researchers, and research trends in this field, and promoting future research and Clinical application.

Materials and Methods

Data Source and Search Strategy

We conducted a search of the Web of Science Core Collection Database for literature on acupuncture for fibromyalgia. The retrieval date was May 30, 2022, and included articles published between January 1, 1990 and May 30, 2022. The search strategy was as follows: topic= (acupuncture OR acupuncture points OR electroacupuncture) AND topic= (fibromyalgia OR fibromyalgia syndrome OR FMS). No restrictions were imposed on language or type of article. Although some article types may offer little information, this approach provides a more comprehensive representation of the range of sample data. Duplicate studies were removed, but no studies were removed for other reasons. All the information, including the number of paper and citation, title, authors, affiliations, countries, keywords, references, publication year and journal were collected for bibliometric analysis.

Statistical Analysis

Microsoft Office Excel (version 2019), VOSviewer (version 1.6.18) and CiteSpace (version 5.8.R3) were used to perform the bibliometric analysis.

Microsoft Office Excel (version 2019) was used to manage data and create a chart showing annual research output.

VOSviewer is a bibliometrics software developed by Van Eck and Waltman.^15,16 In this study, we used VOSviewer to visualize collaborations and time trends among countries, institutions and authors, as well as the journals in which the articles were published. The size of nodes in the map represents the number of publications, the thickness of lines represents the strength of the link and different colors of nodes represent different clusters or times. In order to build a clear visualization network, the number of visualization items in each research topic was limited according to the respective conditions. For example, in the visual network map of co-authored countries, only countries/regions with more than five publications were displayed.

CiteSpace is a bibliometric software developed by Professor Chen Chaomei.¹⁴ In this study, we used CiteSpace for co-citation, cluster and co-occurrence analysis, dual map overlay of journals, and citation burst strength detection. Co-citation analysis of authors, journals, and references can provide an overview of the knowledge base in the field. Cluster analysis can categorize references and identify important research directions in the field of acupuncture for fibromyalgia. The Modular Q and mean silhouette S are two important evaluation indicators in cluster analysis. When Q>0.3, the clustering structure is sufficiently significant, and when S>0.5, the clustering results are credible. Keyword co-occurrence analysis and citation burst strength detection for keywords and references help to demonstrate the research priorities, research hotspots and future research trends in this field. In addition, centrality is a key parameter to measure the importance of a node, and nodes with high centrality are often regarded as turning points or key points in the field. Thus, in this study, CiteSpace was also used to calculate the centrality of cited authors, cited references, and co-occurrence keywords. The parameters of CiteSpace were set as follows: link retaining factor (LRF=3), look back years (LBY=−1), e for top N (e=3), time span (1990–2022), years per slice (4), links (strength: cosine, scope: within slices), selection criteria: g-index (k=25) and pruning (minimum spanning tree).

Results

Analysis of Annual Publications

A total of 280 publications related to this study were retrieved from the database, including 188 articles, 57 reviews, 13 letters, eight proceeding papers, eight editorial materials, six meeting abstracts, six news items and five book chapters (Table 1). The number of publications published each year is shown in Figure 1. We arbitrarily divide the period from 1990 to 2022 into two stages according to the annual output. 1990 to 2005 may be seen as the first phase, in which the total number of publications was less than 10 per year. 2006 to 2022 may be seen as the second phase, in which the total number of publications was probably more than 10 per year, and reached a peak in 2020 (n=28), with more than the total number of articles published in the previous 10 years (1990–1999, n=24). In summary, the number of publications showed an overall upward trend.

Table 1 Document Types for Documents on Acupuncture for Fibromyalgia

Figure 1 The number of annual publications on acupuncture for fibromyalgia indexed by the Web of Science Core Collection Database.

Analysis of Countries/Regions

From 1990 to 2022, 30 countries published research articles on acupuncture for fibromyalgia. For better visualization, 12 countries or regions with more than five articles were selected via VOSviewer (Figure 2 and Table 2). The United States showed the highest output, publishing a total of 105 articles, followed by the People’s Republic of China (28 articles), Germany (23 articles) and England (23 articles). The country with the most cited published articles was also the United States (cited 4815 times), followed by England (1071 times), and Germany (736 times). The visualized international collaboration network showed limited cooperation among countries in this area. Furthermore, as shown in Figure 3, Western developed countries such as the United States, England, Germany, Canada and Sweden started research in this field earlier, while the research on acupuncture for fibromyalgia in developing countries such as the People’s Republic of China and Brazil began in the past 10 years.

Table 2 The Top 10 Productive Countries/Regions Concerning Acupuncture for Fibromyalgia

Figure 2 Map of active countries/regions on acupuncture for fibromyalgia.

Figure 3 Map of active countries/regions on acupuncture for fibromyalgia in terms of time.

Analysis of Institutions

A total of 414 research institutions were involved, and 17 institutions with more than five papers were chosen for visualization (Figure 4). The top 10 institutions with the highest output are shown in Table 3. The China Medical University (published 18 articles) was the leading institution in terms of output, followed by the University of Michigan (12 articles), the University of Exeter & Plymouth (10 articles) and China Medical University Hospital (10 articles). The citation frequency of the University of Michigan in the United States (cited 1487 times) was the highest, followed by the University of Maryland School of Medicine (1191 times) and David Geffen School of Medicine at the University of California Los Angeles (904 times). The visualized institutional collaboration network showed cooperation among institutions with distinct cluster characteristics, and the distance between each cluster was relatively long, which meant that the international cooperation among institutions were not close enough, and global cooperation has not yet formed. Figure 5 shows institutions’ involvement in research in this field over time. The University of Maryland initiated relevant studies at an early stage, and from 2010 research on acupuncture for fibromyalgia was conducted by the China Medical University and China Medical University Hospital. In addition, the geographical focus of research in this field gradually shifted to the East, especially to Asia, after 2010.

Table 3 The Top 10 Institutions Concerning Acupuncture for Fibromyalgia

Figure 4 Map of institutions on acupuncture for fibromyalgia.

Figure 5 Map of institutions on acupuncture for fibromyalgia in terms of time.

Analysis of Authors and Co-Cited Authors

A total of 1012 authors published the included articles, and we selected 39 authors with more than three papers for visual analysis (Figure 6). The top 10 authors publishing articles in this field are listed in Table 4. Lin Yi-wen (published 12 articles) was identified as the most active author in this field, followed by Langhorst (9 articles), Harris (8 articles) and Hauser (8 articles). However, it can be seen from the author cooperation network map that the degree of cooperation between authors in this field was not close enough, mainly within the same institution.

Table 4 The Top 10 Authors Who Study Acupuncture for Fibromyalgia

Figure 6 Map of authors who study acupuncture for fibromyalgia.

Co-citation refers to two or more articles being simultaneously cited in other article. The map of cited authors shows a total of 469 authors whose articles were cited in these 280 included articles (Figure 7). The top 10 co-cited authors in frequency and centrality are listed in Table 5. Wolfe had the most cited frequency (cited 114 times), mainly dedicated to standardizing the diagnostic criteria for fibromyalgia,^7,17,18 which has made significant contributions to the field of acupuncture for fibromyalgia. Deluze (cited 63 times) and Berman (50 times) had the next highest citation frequencies. Manheimer (0.21) had the highest centrality, and was mainly engaged in the research on acupuncture for knee osteoarthritis, low back pain and other rheumatic diseases,^19,20 followed by Appelbaum (0.15) and Berman (0.14). Among the top 10 authors by citation frequency and centrality, all were based in Europe and America except for Martin (South Africa).

Table 5 The Top 10 Frequency and Centrality of Cited Authors Related to Acupuncture for Fibromyalgia

Figure 7 Map of cited authors related to acupuncture for fibromyalgia.

Analysis of Journal and Co-Cited Journal

All of the included articles on acupuncture for fibromyalgia were published in 136 journals. For better visualization, we selected 36 journals producing more than three papers (Figure 8). The top 10 journals with the highest productivity are shown in Table 6, and about 29% of articles in this field were published in these 10 journals. Evidence-Based Complementary and Alternative Medicine was the most productive journals (published 16 papers), followed by Journal of Alternative and Complementary Medicine (15 papers) and Acupuncture in Medicine (9 papers). According to the Journal Citation Reports (2020), the average impact factor (IF) of these top 10 journals was 3.926, indicating that it remains challenging to publish research in this field in high-impact journals. The journal Rheumatology had the highest IF at 7.580 and is a professional journal in this field.

Table 6 The Top 10 Journals on Acupuncture for Fibromyalgia

Figure 8 Map of journals producing publications about acupuncture for fibromyalgia.

A cited journal map was generated for 427 journals (Figure 9). The top 10 co-cited journals are shown in Table 7. The journal Pain was most cited, followed by Arthritis & Rheumatology and Journal of Alternative and Complementary Medicine. The cited journals were mainly in the field of neurosciences, rheumatology and integrative and complementary medicine.

Table 7 The Top 10 Co-Cited Journals on Acupuncture for Fibromyalgia

Figure 9 Map of co-cited journals producing publications about acupuncture for fibromyalgia.

The dual-map overlay (Figure 10) shows that the majority of journals that published articles in this field include three subjects: medicine/medical clinical, neurology/sports/ophthalmology and molecular/biology/immunology. Within these fields, the circles representing the medical/medical clinical fields were larger, indicating a relatively large number of co-authors and published publications. Most of the cited articles came from journals in the fields of molecular/biology/genetics, health/nursing/medicine, sports/rehabilitation and psychology/education/social. The lines in the figure represent the links between citing publications and cited references. The fields molecular/biology/genetics and health/nursing/medicine were cited more frequently by publications in other fields, indicating that these two fields had an important position in the cited references of acupuncture for fibromyalgia research.

Figure 10 The dual-map overlay of citing journals and cited journals on articles related to acupuncture for fibromyalgia. (The left side were the citing journal, the right side were the cited journal, and the line path represents the citation relationship).

Analysis of Co-Cited References

A total of 491 references (Figure 11) were generated from 280 papers. A cluster analysis (Figure 12) was performed on the visual network of co-cited references, and was combined with the context of the literature content to provide a total of nine main clusters (Table 8). The modularity Q was 0.8081, and the weighted mean silhouette S was 0.9436, indicating that the clustering results are credible. The results show that most of the research in these fields was conducted after 1990. Early research directions are Cluster 5 “non-pharmacological intervention”, Cluster 3 “prevalence of alternative medicine” and Cluster 7 “pharmacological intervention” with most published before 2000. There are followed by Cluster 1 “efficacy of alternative medicine”, Cluster 8 “muscle” and Cluster 6 “acupuncture analgesia”, mostly representing research conducted between 2000 and 2010. Cluster 0 “randomized controlled trial (RCT)” and Cluster 2 “acupuncture and fibromyalgia” are long standing research topics in this field. Finally, Cluster 4 “mechanism of acupuncture analgesia” is the focus of the most recent publications. More specific information about each cluster is shown below.

Table 8 Cited Reference Concerned with Acupuncture for Fibromyalgia That Details of Knowledge Clusters

Figure 11 Map of co-cited references related to acupuncture for fibromyalgia.

Figure 12 Cluster map of cited references based on label clusters with title terms.

Articles included in Cluster 5 “non-pharmacological intervention”, described the efficacy of non-pharmacological interventions for fibromyalgia, including biofeedback training, psychological interventions, aerobic exercise and stress management therapy; those in Cluster 3 “prevalence of alternative medicine”, focused on the prevalence and frequency of use of alternative medicine among patients, as well as the per capita cost of alternative medicine. The researchers found that the use of alternative medicine and spending as a share of total health care expenditures has increased since 1990, largely attributable to an increase in the proportion of the population seeking alternative treatments rather than an increase in the number of visits per patient; research in Cluster 7 “pharmacological intervention”, primarily evaluated the efficacy of pharmacological interventions for fibromyalgia, including opioids, nonsteroidal anti-inflammatory drugs (NSAIDs) and norepinephrine reuptake inhibitors, through double-blind randomized controlled trials; articles in Cluster 1 “efficacy of alternative medicine” include, mixed reviews of the effectiveness of acupuncture for fibromyalgia, but generally favor positive outcomes; in Cluster 8 “muscle”, research demonstrated through clinical trials that acupuncture can have an effect on blood flow to the skin and muscles of patients with fibromyalgia. Both subcutaneous acupuncture and deep muscle acupuncture increase the blood flow to the trapezius, tibialis anterior muscle and the skin of this area, with similar efficacy. In addition, the researchers found that blood flow to the deep muscles was positively correlated with muscle pressure pain thresholds; studies in Cluster 6 “acupuncture analgesia” were focused on the analgesic effect of acupuncture on low back pain, knee osteoarthritis and other rheumatic diseases. However, most of the literature in this cluster was not highly correlated with fibromyalgia; in Cluster 0 “randomized controlled trial”, investigated the efficacy of various acupuncture treatments, such as electroacupuncture, formula acupuncture, manual acupuncture, and sham acupuncture for fibromyalgia. Findings were mixed, but skewed toward positive results. Researchers found that acupuncture not only improved pain, but may also have beneficial effects on anxiety, fatigue, and insomnia; article in Cluster 2 “acupuncture and fibromyalgia” were cited primarily by RCTs on acupuncture for fibromyalgia, covering topics such as expert consensus on acupuncture treatment, development and validation of a fibromyalgia-related assessment questionnaire, and systematic reviews of acupuncture for fibromyalgia; Cluster 4 “mechanism of acupuncture analgesia” includes mainly studies on the mechanism of acupuncture analgesia. These studies found through animal experiments that electroacupuncture at a specific frequency can promote the release of specific neuropeptides in the central nervous system, and may interfere with the metabolism of adenosine and inhibit the activation of related signaling pathways in the central nervous system to relieve pain.

Table 9 shows the top 10 references by citation frequency and centrality. Among the top 10 most cited references, six were clinical trials and four were systematic reviews. Seven of these 10 focused on the clinical efficacy of acupuncture for fibromyalgia, two were on the diagnostic criteria for fibromyalgia, and one study investigated the effects of different acupuncture sites, stimulation intensity, and acupuncture frequency on fibromyalgia. Among the top 10 cited references for centrality, six were clinical studies, three were systematic reviews and one was questionnaires based. Four of the 10 focused on the clinical efficacy of acupuncture for fibromyalgia, one was on the diagnostic criteria for fibromyalgia; one on its pathogenesis, one on complementary and alternative treatments for fibromyalgia, one investigated the effects of different acupuncture sites, stimulation intensity, and acupuncture frequency on fibromyalgia; one was on the mechanisms by which acupuncture and sham acupuncture relieve fibromyalgia, and one was on the prevalence and per capita cost of alternative therapy in the United States. Therefore, the clinical efficacy of acupuncture for fibromyalgia has always been the focus of research in this field.

Table 9 The Top 10 Frequency and Centrality of Cited References Related to Acupuncture for Fibromyalgia

Figure 13 shows the top 15 references with citation burst, aside from the newly revised diagnostic criteria for fibromyalgia published by the ACR in 2010.¹⁸ The article with the highest-cited outbreak was Berman (1999),²¹ a systematic review which showed that acupuncture was more effective than sham acupuncture for pain relief in patients with fibromyalgia, increasing pain threshold, and reducing morning stiffness, but the duration of sustained benefit after acupuncture was unclear. Since 2018, two articles with high citation bursts, Vas (2016)²² and Karatay (2018)²³ both demonstrated through RCTs that acupuncture, but not sham acupuncture, was effective in relieving fibromyalgia. In addition, Vas (2016) found through follow-up that the pain relief effect of acupuncture can persist for 1 year, while Karatay (2018) proposed that changes in the level of serum pain neuromediators may be one of the mechanisms by which acupuncture affects fibromyalgia. The surge in citations for these two studies also suggests that investigating the duration of benefit after acupuncture and the effects of acupuncture on pain neuromediator levels in patients with fibromyalgia are potential leading research directions in this field.

Figure 13 Top 15 references with the strongest citation bursts.

Analysis of Keywords

We extracted a total of 282 co-occurrence keywords from the data for visual analysis (Figure 14). Table 10 shows the top 10 co-occurrence keywords by frequency and centrality. The highest frequency keyword was fibromyalgia (71 times), followed by acupuncture (66 times) and pain (52 times). This suggests that verifying whether acupuncture can relieve pain symptoms in patients with fibromyalgia remains a research focus in this field. The highest centrality keyword was chronic pain (0.21), followed by management (0.19) and back pain (0.15). Fibromyalgia has been defined as a chronic systemic musculoskeletal pain disorder in which the back is one of the main pain sites. The management of fibromyalgia has always been an important part of guidelines related to fibromyalgia, and non-pharmacological therapies, including acupuncture, are the first-line clinical treatment recommended by the guidelines. For patients with poor response to non-pharmacological therapy, supplementary drug therapy, such as antidepressants, muscle relaxants and others are recommended. We subsequently performed a keyword citation burst detection analysis and extracted a total of 20 keywords (Figure 15). The result showed that the keyword “criteria” had the largest burst intensity in the field. This was closely related to the development of the diagnostic criteria for fibromyalgia. In 2010, the ACR revised the diagnostic criteria for fibromyalgia, bringing about changes in the entire field of fibromyalgia research.¹⁸ In addition, mechanism, spinal cord, activation and sensitivity have relatively high burst strengths in recent years. These four keywords are closely related to the mechanism of acupuncture for fibromyalgia. Studies have shown that in a rat model of fibromyalgia, neurons in the spinal cord were hyperactivated, exhibiting higher background firing and increased mechanical responses, as well as increased excitatory synaptic input and decreased inhibitory synaptic input, resulting in nociceptive hypersensitivity reactions.²⁴ Acupuncture can down-regulate the phosphorylation levels of two subtypes of N-methyl-aspartate receptors (NMDARs), NR1 and NR2, and down-regulate the expression levels of transient receptor potential vanilloid 1 (TRPV1) and TRPV4 in the spinal cord to alleviate pain in mice with fibromyalgia.^25–27 In addition, acupuncture can exert analgesic effect by increasing the pain threshold and reducing pain sensitivity in patients with fibromyalgia.²⁸ Finally, since 2018, the keyword “meta-analysis” also has high burst strength. As research on acupuncture for fibromyalgia increases, timely meta-analysis and systematic reviews of new findings are warranted.

Table 10 The Top 10 Frequency and Centrality of Co-Occurrence Keywords Related to Acupuncture for Fibromyalgia

Figure 14 Map of co-occurrence keywords related to acupuncture for fibromyalgia.

Figure 15 Top 20 keywords with the strongest citation bursts.

Discussion

In this study, we used a bibliometric approach to analyze trends and directions of research on acupuncture for fibromyalgia between 1990 and 2022. By combining collaboration network, co-citation network, co-occurrence network and burst analyses, we found low cooperation between countries and institutions, indicating that international cooperation should be further promoted, and direct cooperation between hospitals and scientific research institutions should be encouraged. Because there is currently no cure for fibromyalgia, long-term acupuncture treatment may be necessary for symptomatic relief. Through cooperation between hospitals and scientific research institutions, sharing data resources and improving the long-term follow-up observation of fibromyalgia patients, to clarify the reasonable setting of acupuncture courses, the interval between courses, the medical cost required to maintain such a treatment plan, and optimize current guidelines for alternative medicine treatment of fibromyalgia. In addition, in terms of research trends, the field has developed from studies on the clinical efficacy of acupuncture for fibromyalgia to exploring the mechanism of acupuncture for fibromyalgia. With regard to future research in this field, three points deserve further exploration.

Firstly, previous clinical studies have reached different conclusions on the difference between efficacy of acupuncture and sham acupuncture for fibromyalgia. This may reflect differences in the design of RCTs, including the inclusion criteria, the design of the sham acupuncture, the selection of acupuncture points in the acupuncture group, and the follow-up period. Studies have shown that the pain pressure threshold of subjects can affect the effect of acupuncture and sham acupuncture. Patients with higher pain pressure threshold showed better analgesic effect of acupuncture, while those with lower pain pressure threshold showed better analgesic effect after sham acupuncture.²⁹ The rational design of sham acupuncture has also been controversial in the academic circles. The common sham acupuncture designs in the past include conventional acupuncture at non-acupoints, acupuncture at acupoints but only lightly piercing the skin, or simulated acupuncture at acupoints without penetrating the skin. Some researchers believe that it may be unreasonable to simply select points far away from acupoints for sham acupuncture.³⁰ These points may puncture other meridians or acupoints, and it is difficult to find truly ineffective acupoints.³⁰ In addition, the width of the meridians is unclear.³⁰ Other studies have found that subcutaneous acupuncture can cause changes in local blood flow.^31,32 On the selection of acupoints in the acupuncture group, there is currently no generally recognized dominant acupoint group, so it is impossible to determine whether the acupoints selected in the trial have superior curative effects.³⁰ Regarding follow-up periods, studies have found that both acupuncture and sham acupuncture can relieve fibromyalgia, but the effect may persist for 3 months in the acupuncture group but not the sham group.²³ In conclusion, standardized, reasonable and rigorous RCTs design may be the key to further clarify the difference in clinical efficacy between acupuncture and sham acupuncture on fibromyalgia.

Secondly, an important future research focus may be to further explore whether acupuncture can effectively improve the accompanying symptoms of fibromyalgia of different severities, and reduce the risk of comorbidities in patients with fibromyalgia. Previous research has found that acupuncture can effectively improve fatigue and sleep quality in patients with high-severity fibromyalgia that is refractory to conventional pharmacological therapy. Unfortunately, most of the patients in that research were also receiving drug treatment, and there was no corresponding control group, which made it difficult to evaluate the true efficacy of acupuncture.³³ Therefore, follow-up studies are needed to further explore the efficacy of acupuncture on fibromyalgia of different severities, especially the benefit in patients with fibromyalgia who are refractory to conventional medical therapy. In addition, the accompanying symptoms of fibromyalgia include fatigue, sleep disturbance, anxiety, depression, balance disturbance and others. Previous studies have focused on the effects of acupuncture on fatigue, sleep disturbance, anxiety and depression.^12,13 With the increasing number of studies on balance disorders in fibromyalgia patients in recent years,^2,34 researchers in this field have also begun to pay attention to the effects of acupuncture on balance disorders in fibromyalgia. Research has shown that acupuncture improves dynamic equilibrium and postural control in women with fibromyalgia, with effects sustained for 5 weeks.³⁵ However, research on the efficacy of acupuncture on balance disorders in fibromyalgia is still at an early stage, and more clinical studies with large samples, multi-center and rigorous trial designs are needed for further verification. The comorbidities of fibromyalgia, including diabetes, high blood pressure, heart disease, irritable bowel syndrome, migraines and others, also represent a significant health care concern. Retrospective studies showed that acupuncture reduces the risk of coronary heart disease and stroke in Taiwanese patients with fibromyalgia.^36,37 It is well known that acupuncture is a non-pharmacological therapy that works through multiple targets. Therefore, it is important to explore whether acupuncture can reduce the risk of other comorbidities in patients with fibromyalgia through retrospective studies, prospective RCTs and basic scientific research.

Finally, research on the central analgesic mechanism of acupuncture on fibromyalgia is a relatively new research direction. Fibromyalgia is generally believed to be systemic pain caused by central nervous system dysfunction.^38,39 In recent years, researchers in this field have begun to further explore the central analgesic mechanism of acupuncture on fibromyalgia through animal experiments and neuroimaging techniques. Bibliometric analysis found 11 studies in this field that use animal experiments to investigate the central analgesic mechanism of acupuncture, and all experimental animal models were induced by acidic saline and intermittent cold stress.^{26,27,40–48} However, although acidic saline-induced, reserpine-induced, and intermittent cold stress-induced experimental animal models were the three most common animal models of fibromyalgia.⁴⁹ The reserpine-induced models can develop spontaneous nociception and only respond to recommended fibromyalgia medications, not to opioids and NSAIDs.⁴⁹ In contrast, experimental animal models induced by acidic saline and intermittent cold stress are free of spontaneous nociception and respond to recommended fibromyalgia medications, opioids, and NSAIDs.⁴⁹ Therefore, the reserpine model may be the closest animal model to the clinical manifestations of fibromyalgia.⁴⁹ Of course, since the clinical manifestations of fibromyalgia are complex and diverse, and the pathogenesis is unknown, there is no animal model that can completely model the clinical symptoms of fibromyalgia, so the selection of model must be based on the symptoms or mechanisms to be studied. In addition, one study using neuroimaging techniques found that electroacupuncture increased the connection between the trunk sensory cortex and the anterior and posterior insula in patients with fibromyalgia, which in turn led to increased GABA levels in the anterior insula and relieved pain symptoms.⁵⁰ At present, there are few studies in this area. Future research should continue to use neuroimaging techniques to study the role of the central nervous system or related neurotransmitters in acupuncture for fibromyalgia.

The use of both CiteSpace and VOSviewer to conduct the literature visualization analysis and provide a reference for researchers is a strength of the present study. However, the study also has some limitations. First, we retrieved data only from the Web of Science Core Collection database, not other large databases such as Embase and Scopus. This was because neither CiteSpace nor VOSviewer can analyze data from multiple databases simultaneously. Second, our search strategy may not have yielded all publications on acupuncture for fibromyalgia in the Web of Science Core Collection database. Finally, while some of the data were processed manually, most of the results of this study are based on machine algorithms, so the data used to support our results may be biased.

Conclusion

Acupuncture can effectively relieve pain in patients with fibromyalgia and improve accompanying symptoms such as anxiety and depression. However, this field is at an early stage of development. Further optimization of clinical trial design is needed to better verify the efficacy of acupuncture on various clinical symptoms of fibromyalgia, and exploration of the central analgesic mechanism of acupuncture for fibromyalgia is an important focus for current and future research in this field.