Psychotherapy for Physical Pain in Patients with Fibromyalgia: A Systematic Review

Gómez-de-Regil, Lizzette; Estrella-Castillo, Damaris F.

doi:https://doi.org/10.1155/2020/3408052

Pain Research and Management

On this page

Abstract Introduction Methods Results Discussion Conclusions Conflicts of Interest Acknowledgments References Copyright Related Articles

Review Article | Open Access

Volume 2020 | Article ID 3408052 | https://doi.org/10.1155/2020/3408052

Psychotherapy for Physical Pain in Patients with Fibromyalgia: A Systematic Review

Lizzette Gómez-de-Regil¹and Damaris F. Estrella-Castillo²

Academic Editor: Jacob Ablin

Received10 Apr 2020

Accepted27 May 2020

Published04 Jul 2020

Abstract

Objective. To provide a brief and comprehensive summary of the recent evidence from clinical trials testing psychotherapeutic interventions in patients with fibromyalgia with particular interest in their possible effect on physical pain. Methods. Bibliographical search was performed in PubMed, PsycInfo, Web of Science, Scopus, and Cochrane Library databases. Content of the manuscripts was studied to obtain, if available, the following information: year of publication, location of the research team, design, type of psychotherapeutic intervention tested, pain measures, and a brief description of the psychotherapy, groups, and outcomes regarding physical pain. Results. Initial search eliciting 475 citations got reduced to 13 relevant papers. Most research studies from Spain (n = 8) are randomized control trials (n = 10) and used guided imagery (n = 5) or cognitive behavioral therapy (n = 4). The Visual Analogue Scale (n = 4) and the Fibromyalgia Impact Questionnaire (n = 4) were the physical pain measures mostly used. Improvements on physical pain were reported on all studies with published results; nevertheless, only in five cases, differences were significant. Conclusions. Evidence on the effect of psychotherapy on physical pain in patients with FS was divergent; though most studies report a reduction in pain, this was not always lasting and/or significant. Diversity of the results might be due to the selected psychotherapeutic approaches, assessment tools, and other internal (e.g., personality traits, (sub)clinical psychiatric symptoms, and treatment adherence) and external (e.g., family environment and social support) variables worth to be considered in the future research.

1. Introduction

Fibromyalgia syndrome (FS) is a term used for identifying a physical condition characterized by chronic widespread pain perceived at musculoskeletal sites, often associated with poor sleep, fatigue, and depression [1,2]. A recent review on FS prevalence found values in the general population between 0.2 and 6.6%, in women between 2.4 and 6.8%, in urban areas between 0.7 and 11.4%, and in rural areas between 0.1 and 5.2% [3]. Despite its significant occurrence, its acknowledgment and delineation as a distinctive clinical disorder is relatively recent; in 1990, the American College of Rheumatology (ACR) provided the first classification criteria for FS [4] that was later updated [5] and modified [6]. In 1992, the World Health Organization officially coded FS for the first time, including it in the tenth Revision of the International Statistical Classification of Diseases and Related Health Problems (ICD-10).

FS is unlikely to resolve; less than 50% of patients achieve complete symptomatic relief, and less than 30% reach complete remission after 3 years of the diagnosis [1,7]. Thus, the current treatment alternatives mostly aim at managing pain and improving functionality and quality of life. Habitually, medical treatment prescribes antidepressant, antiepileptic, and analgesic drugs with modest benefits [8,9]. Nonpharmacologic therapies (e.g., cognitive behavioral therapy, psychoeducation, exercise, and vitamin D intake) and complementary therapies (e.g., tai chi, acupuncture, and manual or hydrotherapy) can provide further alleviation of physical and psychological symptoms [10,11].

Pain is the hallmark symptom in FS; yet, its cause is still unknown. Evidence suggests a multifactorial etiology in which central pain sensitization, disordered hypothalamic-pituitary-adrenal axis, vegetative tone anomaly, and sleep disturbance interplay as the FS pain triggers, mainly by the result of a reduced pain threshold [1,12]. Patients with FS experience continuous pain, not only physical, but also emotional. The use of antidepressant drugs and psychotherapy has shown favorable results in the amelioration of symptoms, suggesting a close link between the physical and the psychological dimensions of the syndrome [13].

Various studies have analyzed specific personality traits and/or psychiatric conditions (i.e., personality and/or mental disorders) that could be present in higher percentages in patients with FS. Studies report high levels of alexithymia (difficulty in recognizing and describing one’s own emotions and feelings) and type D/distressed personality (elevated propensity to psychological distress due to a constant tendency to experience negative emotions across different life circumstances, called negative affectivity, and the restricted expression of emotions and behaviors in social interaction, called social inhibition) in patients with FS. Nevertheless, when depression is controlled, the results do not seem to differ from those of healthy controls [14]. Regarding psychopathology, the proportion of personality disorders appears far greater in patients with FS than in the general population, mainly obsessive-compulsive, avoidant, histrionic, and borderline personality disorders [15]. Moreover, compared with controls, patients with FS show a higher prevalence of mental disorders, particularly depression and anxiety, reported in 20–80% and 13–63.8% of cases, respectively [13].

From the field of psychology, researchers and professionals have worked intensively on the design, implementation, and testing of psychotherapeutic interventions in patients with FS [16]. Diverse psychological interventions have shown favorable results, from cognitive behavioral approaches [17,18] to psychoeducational [19] and mind and body therapies [20].

Given their particular health conditions, patients with FS may benefit from professional psychological support not only to deal with emotional issues directly or indirectly related to their illness, but also to manage physical pain, a frequent and disruptive symptom characterizing FS. This review presents a brief and comprehensive summary of the recent evidence from clinical trials testing psychotherapeutic interventions in patients with FS with particular interest in their possible effect on physical pain, a topic of potential interest to professionals working with this population and for patients themselves.

2. Methods

The review was performed according to the PRISMA statement (preferred reporting items for systematic reviews and meta-analyses [21]. A bibliographical search was performed in the PubMed, PsycInfo, Web of Science, Scopus, and Cochrane Library databases, February 20-21, 2020. The term “fibromyalgia” was entered in combination with “psychotherapy” and “pain,” restricted to title, abstract, and/or keywords when the option was available. Inclusion criteria were (1) research papers, (2) published in peer-reviewed journals, (3) available in English or Spanish, and (4) published during the last decade (2010 to February 2020). Exclusion criteria were (1) not original research (e.g., summaries, guidelines, reviews, and/or meta-analyses), (2) papers unrelated to the topic, (3) research not applied specifically to patients with FS and/or not using a psychotherapeutic intervention, and (4) physical pain was not included as an outcome measure. Publication relevance was verified based on the study objective. Citations for publications other than research articles (e.g., commentary, erratum, and book chapters) were excluded, and also articles reporting updates, (systematic) reviews, and/or meta-analyses. Abstracts were read to make a further cut of publications reporting research not clearly related to patients with FS and/or not focused on psychotherapeutic intervention. The full content of manuscripts was consulted to verify that physical pain was considered as an outcome measure of the interventional study. Papers reporting study protocols were included, considering that, even though they do not provide empirical evidence, they may offer a detailed description of the study design and the intervention, and their results are expected to be published afterwards. Once a final reference list was generated, the following information was obtained from each article: year of publication, location of the research team, design, type of psychotherapeutic intervention tested, pain measures, and a brief description of the psychotherapy, groups, and outcomes regarding physical pain. Both authors worked together through the procedure; discrepancies were minimal.

3. Results

The initial search from the five selected databases elicited 475 citations with 128 duplicates. Through the review of available abstracts, the list reduced to 31 research papers addressing psychotherapeutic interventions in patients with FS, and only 15 papers considered physical pain as an outcome measure. Then, two references of study protocols were excluded as they were not published in peer-reviewed journals. The final sample included 13 publications (Figure 1), with 11 original research manuscripts and two study protocols.

Table 1 summarizes the basic features of the publications. Most research comes from Spain (n = 8), followed by the United States (n = 2) and single contributions from Italy, the Netherlands, and Chile. Randomized control trials (RCT) are the most common design, 8 with two arms and 2 with three arms. Three studies used a single group design. Guided imagery was the most common psychotherapeutic intervention (n = 5), followed by cognitive behavioral therapy (CBT) (n = 4). The Visual Analogue Scale (VAS) (n = 4) and the specific items from the Fibromyalgia Impact Questionnaire (FIQ) (n = 4) were the physical pain measures mostly used. Others were the McGill Pain Inventory and the Brief Pain Inventory.

Table 2 presents brief information on interventions and their effect on physical pain. Most interventions were provided in weekly individual and/or group sessions, in small groups of 5 to 8 participants. Although only one research reported psychoeducation as an intervention, some others included psychoeducational topics as part of the program. The use of technology to provide psychotherapeutic treatment, for instance, recorded scripts and the implementation of a virtual reality environment, are mentioned. Regarding the effect of the psychotherapeutic intervention on physical pain, five publications reported a significant reduction in comparison with the control groups. One publication reported a significant improvement on physical pain, but not lasting. Five publications reported pain reduction but not at a significant level. Table 3 summarizes the results on physical pain scores.

Additionally, both authors independently scored the studies using the scale for rating the quality of psychological trials for pain developed by Yates and colleagues [35]. Interrater reliability by the intraclass correlation coefficient (by the two-way mixed model and absolute agreement) was 0.95 (95% CI = 0.82–0.99) for the full scale, 0.65 (95% CI = 0.09–0.89) for treatment quality, and 0.97 (95% CI = 0.86–0.99) for methodological quality. Scores by raters are presented in Table 4.

4. Discussion

Fibromyalgia is not an uncommon syndrome, particularly among women [1,2]. On a daily basis, patients must face discomfort and pain in tender points throughout their bodies. Multidisciplinary treatment is recommended, including psychiatric/psychological services, as patients may experience mild to severe symptoms of depression and anxiety [36]. Furthermore, the use of antidepressants has shown improvements not only in the emotional state, but also in the self-perceived level of physical pain. This supports the idea of a possible connection between the physical and the psychological experiencing of pain in FS [13]. This review aimed at summarizing the recent evidence regarding psychotherapeutic interventions in patients with FS and their effect on physical pain.

The search found 13 publications on the topic; nevertheless, none of the psychotherapeutic interventions was specifically designed for the management of physical pain. Most studies followed a randomized control trial design that improves the reliability of the findings. In terms of outcomes, although in most cases physical pain was reduced, no effects of psychotherapeutic intervention could be established [22,23,26,28,29,32]. On the other hand, five studies found significant differences by the end of the treatment [27,30] and up to 3-month [24,31] and 12-month follow-ups [25]. Evidence is ambiguous; results could be influenced by the study design and the type of psychotherapeutic intervention, among other variables. It must be pointed out that physical pain was not the target outcome the interventions were designed for, and yet, in some cases, a significant effect was found. Further studies could focus on designing psychotherapeutic interventions for the amelioration of physical pain as a primary outcome, adapting contents and instruments to this objective.

Regarding the type of interventions, results show that guided imagery and CBT are the most common approaches. Imagery has been defined as “a mental function and a live experience that is a dynamic, quasireal, and psychophysiological process” [37]. Through imagery, initiated by the patient or guided by a therapist, the person creates and experiences an internal reality, regardless of the external stimuli, with the purpose of promoting adaptive changes in sensations, emotions, thoughts, or behaviors [38]. A recent meta-analysis by Zech and colleagues [39] found that guided imagery had a relevant benefit compared to controls on ≥50% pain relief at the end of therapy. Here, two studies found a significant effect on pain reduction at the end of the treatment [27,30] and one up to a 3-month follow-up [31], while other two studies could not establish a significant effect [29,32]. Guided imagery should be considered as a promising approach, not only for the available results in favor, but also due to the minimal economic cost of the intervention and that, once learned, the patient can continue practicing by him/herself. CBT assumes that negative emotions result from dysfunctional ideas framed by the person’s system of beliefs. Therefore, CBT interventions guide the patients to identify those distorted beliefs that may influence the severity of the symptoms and to compromise to behavioral and cognitive changes, substituting dysfunctional schemes [40]. This review elicited three studies reporting on the use of CBT in patients with FS; nevertheless, none of them was targeted to reduce physical pain. Herrero and colleagues [23] proposed CBT for promoting positive emotions, showing significant increases in general mood state, positive emotions, motivation, and self-efficacy, but not a significant effect on physical pain. Lami and colleagues [24] developed a CBT program for insomnia in patients with FS; results showed that, regardless of sex, patients showed significant improvements in sleep quality and also in pain intensity. Lumley and colleagues [26] compared CBT and emotion awareness and expression therapy and found that they did not differ on pain severity although the latter led to a significantly lower widespread pain and a higher percentage of patients achieving 50% pain reduction. In a review, Bennet and Nelson [40] concluded that most studies found that CBT led to improvements in pain-related behavior and that sustained improvements were most evident when individualized CBT was used to treat patients with juvenile fibromyalgia. A CBT perspective might well improve the clinical outcome in FS, but not recommended as a single modality [40] but rather in a multidisciplinary program.

5. Conclusions

This systematic review of the recent evidence regarding the effect of psychotherapy on physical pain in patients with FS showed that results are divergent; though most reported a reduction in pain, this was not always lasting and/or significant. Diversity of the results might be due to the selected psychotherapeutic approaches, assessment tools, and other internal (e.g., personality traits, subclinical psychiatric symptoms, and treatment adherence) and external (e.g., family environment and social support) variables, and these are worth to be considered in the future research.

Conflicts of Interest

The authors declare that there are no conflicts of interest regarding the publication of this article.

Acknowledgments

This work was supported by the Hospital Regional de Alta Especialidad de la Península of Yucatán.

References

F. Laroche, P. Sarzi-Puttini, and S. Perrot, “Generalised pain syndromes (including fibromyalgia syndrome and chronic fatigue syndrome),” in EULAR Textbook on Rheumatic Diseases, J. Bijlsma and E. Hachulla, Eds., pp. 1022–1042, BMJ Publishing Group, London, UK, 2015.
View at: Google Scholar
W. Häuser and M. A. Fitzcharles, “Facts and myths pertaining to fibromyalgia,” Dialogues in Clinical Neuroscience, vol. 20, no. 1, pp. 53–62, 2018.
View at: Google Scholar
A. P. Marques, A. d. S. d. E. Santo, A. A. Berssaneti, L. A. Matsutani, and S. L. K. Yuan, “Prevalence of fibromyalgia: literature review update,” Revista Brasileira de Reumatologia (English Edition), vol. 57, no. 4, pp. 356–363, 2017.
View at: Publisher Site | Google Scholar
F. Wolfe, H. A. Smythe, M. B. Yunus et al., “The American College of Rheumatology 1990 criteria for the classification of fibromyalgia. Report of the multicenter criteria committee,” Arthritis Rheum, vol. 33, pp. 160–172, 1990.
View at: Google Scholar
F. Wolfe, D. J. Clauw, M.-A. Fitzcharles et al., “The American College of Rheumatology preliminary diagnostic criteria for fibromyalgia and measurement of symptom severity,” Arthritis Care & Research, vol. 62, no. 5, pp. 600–610, 2010.
View at: Publisher Site | Google Scholar
F. Wolfe, D. J. Clauw, M.-A. Fitzcharles et al., “Fibromyalgia criteria and severity scales for clinical and epidemiological studies: a modification of the ACR preliminary diagnostic criteria for fibromyalgia,” The Journal of Rheumatology, vol. 38, no. 6, pp. 1113–1122, 2011.
View at: Publisher Site | Google Scholar
T. L. Skaer, “Fibromyalgia: disease synopsis, medication cost effectiveness and economic burden,” Pharmacoeconomics, vol. 32, no. 5, pp. 457–466, 2014.
View at: Publisher Site | Google Scholar
R. Kwiatek, “Treatment of fibromyalgia,” Australian Prescriber, vol. 40, no. 5, pp. 179–183, 2017.
View at: Publisher Site | Google Scholar
S. Kia and E. Choy, “Update on treatment guideline in fibromyalgia syndrome with focus on pharmacology,” Biomedicines, vol. 5, no. 4, p. 20, 2017.
View at: Publisher Site | Google Scholar
R. Lauche, H. Cramer, W. Häuser, G. Dobos, and J. Langhorst, “A systematic overview of reviews for complementary and alternative therapies in the treatment of the fibromyalgia syndrome,” Evidence-Based Complementary and Alternative Medicine, vol. 2015, pp. 1–13, 2015.
View at: Publisher Site | Google Scholar
S. Chinn, W. Caldwell, and K. Gritsenko, “Fibromyalgia Pathogenesis and treatment options update,” Current Pain and Headache Reports, vol. 20, no. 4, p. 25, 2016.
View at: Publisher Site | Google Scholar
C. Boomershine, “Fibromyalgia: the prototypical central sensitivity syndrome,” Current Rheumatology Reviews, vol. 11, no. 2, pp. 131–145, 2015.
View at: Publisher Site | Google Scholar
P. Fietta, P. Fietta, and P. Manganelli, “Fibromyalgia and psychiatric disorders,” Acta Bio-Medica: Atenei Parmensis, vol. 78, no. 2, pp. 88–95, 2007.
View at: Google Scholar
C. Conversano, L. Marchi, R. Ciacchini et al., “Personality traits in fibromyalgia (FM): does FM personality exists? A systematic review,” Clinical Practice & Epidemiology in Mental Health, vol. 14, no. 1, p. 263, 2018.
View at: Publisher Site | Google Scholar
L. Attademo and F. Bernardini, “Prevalence of personality disorders in patients with fibromyalgia: a brief review,” Primary Health Care Research & Development, vol. 19, no. 5, pp. 523–528, 2018.
View at: Publisher Site | Google Scholar
W. Häuser and G. Jones, “Psychological therapies for chronic widespread pain and fibromyalgia syndrome,” Best Practice & Research Clinical Rheumatology, vol. 33, no. 3, p. 101416, 2019.
View at: Publisher Site | Google Scholar
V. Köllner, W. Häuser, K. Klimczyk et al., “Psychotherapie von Patienten mit Fibromyalgiesyndrom,” Der Schmerz, vol. 26, no. 3, pp. 291–296, 2012.
View at: Publisher Site | Google Scholar
V. Köllner, K. Bernardy, W. Greiner et al., “Psychotherapie und psychologische Verfahren beim Fibromyalgiesyndrom,” Der Schmerz, vol. 31, no. 3, pp. 266–273, 2017.
View at: Publisher Site | Google Scholar
C. Conversano, A. Poli, R. Ciacchini et al., “A psychoeducational intervention is a treatment for fibromyalgia syndrome,” Clinical and Experimental Rheumatology, vol. 37, no. 1, pp. 98–104, 2019.
View at: Google Scholar
A. Theadom, M. Cropley, H. E. H. E. Smith et al., “Mind and body therapy for fibromyalgia,” in Cochrane Database of Systematic Reviews, A. Theadom, Ed., John Wiley & Sons, Chichester, UK, 2015.
View at: Publisher Site | Google Scholar
D. Moher, A. Liberati, J. Tetzlaff, and D. G. Altman, “Preferred reporting items for systematic reviews and meta-analyses: the PRISMA statement,” PLoS Medicine, vol. 6, no. 7, Article ID e1000097, 2009.
View at: Publisher Site | Google Scholar
C. Endrizzi, C. Di Pietrantonj, G. D’Amico, M. Pasetti, L. Bartoletti, and R. Boccalon, “Dance movement psychotherapy for patients with fibromyalgia syndrome,” Body, Movement and Dance in Psychotherapy, vol. 12, no. 2, pp. 111–127, 2017.
View at: Publisher Site | Google Scholar
R. Herrero, A. García-Palacios, D. Castilla, G. Molinari, and C. Botella, “Virtual reality for the induction of positive emotions in the treatment of fibromyalgia: a pilot study over acceptability, satisfaction, and the effect of virtual reality on mood,” Cyberpsychology, Behavior, and Social Networking, vol. 17, no. 6, pp. 379–384, 2014.
View at: Publisher Site | Google Scholar
M. J. Lami, M. P. Martínez, A. I. Sánchez et al., “Gender differences in patients with fibromyalgia undergoing Cognitive-Behavioral Therapy for insomnia: preliminary data,” Pain Practice, vol. 16, no. 2, pp. E23–E34, 2016.
View at: Publisher Site | Google Scholar
J. V. Luciano, R. Sabes-Figuera, E. Cardeñosa et al., “Cost-utility of a psychoeducational intervention in fibromyalgia patients compared with usual care,” The Clinical Journal of Pain, vol. 29, no. 8, pp. 702–711, 2013.
View at: Publisher Site | Google Scholar
M. A. Lumley, H. Schubiner, N. A. Lockhart et al., “Emotional awareness and expression therapy, cognitive behavioral therapy, and education for fibromyalgia,” Pain, vol. 158, no. 12, pp. 2354–2363, 2017.
View at: Publisher Site | Google Scholar
V. Menzies, D. E. Lyon, R. K. Elswick Jr., N. L. McCain, and D. P. Gray, “Effects of guided imagery on biobehavioral factors in women with fibromyalgia,” Journal of Behavioral Medicine, vol. 37, no. 1, pp. 70–80, 2014.
View at: Publisher Site | Google Scholar
P. Montesó-Curto, M. García-Martínez, C. Gómez-Martínez et al., “Effectiveness of three types of interventions in patients with fibromyalgia in a region of Southern Catalonia,” Pain Management Nursing, vol. 16, no. 5, pp. 642–652, 2015.
View at: Publisher Site | Google Scholar
M. D. Onieva-Zafra, L. H. García, and M. G. Del Valle, “Effectiveness of guided imagery relaxation on levels of pain and depression in patients diagnosed with fibromyalgia,” Holistic Nursing Practice, vol. 29, no. 1, pp. 13–21, 2015.
View at: Publisher Site | Google Scholar
M. D. Onieva-Zafra, M. L. Parra-Fernández, and E. Fernandez-Martinez, “Benefits of a home treatment program using guided imagery relaxation based on audio recordings for people with fibromyalgia,” Holistic Nursing Practice, vol. 33, no. 2, pp. 111–120, 2019.
View at: Publisher Site | Google Scholar
E. Torres, I. N. Pedersen, and J. I. Pérez-Fernández, “Randomized trial of a group music and imagery method (GrpMI) for women with fibromyalgia,” Journal of Music Therapy, vol. 55, no. 2, pp. 186–220, 2018.
View at: Publisher Site | Google Scholar
R. Verkaik, M. Busch, T. Koeneman, R. van den Berg, P. Spreeuwenberg, and A. L. Francke, “Guided imagery in people with fibromyalgia: a randomized controlled trial of effects on pain, functional status and self-efficacy,” Journal of Health Psychology, vol. 19, no. 5, pp. 678–688, 2014.
View at: Publisher Site | Google Scholar
L. Gómez-Pérez, A. Vergés, A. R. Vázquez-Taboada, J. Durán, and M. González Tugas, “The efficacy of adding group behavioral activation to usual care in patients with fibromyalgia and major depression: design and protocol for a randomized clinical trial,” Trials, vol. 19, no. 1, 2018.
View at: Publisher Site | Google Scholar
C. Paz, M. Aguilera, M. Salla et al., “Personal construct therapy vs cognitive behavioral therapy in the treatment of depression in women with fibromyalgia: study protocol for a multicenter randomized controlled trial,” Neuropsychiatric Disease and Treatment, vol. 16, pp. 301–311, 2020.
View at: Publisher Site | Google Scholar
S. L. Yates, S. Morley, C. Eccleston, and A. C. de C Williams, “A scale for rating the quality of psychological trials for pain,” Pain, vol. 117, no. 3, pp. 314–325, 2005.
View at: Publisher Site | Google Scholar
M. Bernik, T. P. A. Sampaio, and L. Gandarela, “Fibromyalgia comorbid with anxiety disorders and depression: combined medical and psychological treatment,” Current Pain and Headache Reports, vol. 17, no. 9, 2013.
View at: Publisher Site | Google Scholar
V. Menzies and A. Gill Taylor, “The idea of imagination: an analysis of “imagery,” Advances in Mind-Body Medicine, vol. 20, pp. 4–10, 2004.
View at: Google Scholar
K. Bernardy, N. Füber, P. Klose, and W. Häuser, “Efficacy of hypnosis/guided imagery in fibromyalgia syndrome-a systematic review and meta-analysis of controlled trials,” BMC Musculoskeletal Disorders, vol. 12, no. 1, 2011.
View at: Publisher Site | Google Scholar
N. Zech, E. Hansen, K. Bernardy, and W. Häuser, “Efficacy, acceptability and safety of guided imagery/hypnosis in fibromyalgia-a systematic review and meta-analysis of randomized controlled trials,” European Journal of Pain, vol. 21, no. 2, pp. 217–227, 2017.
View at: Publisher Site | Google Scholar
R. Bennett and D. Nelson, “Cognitive behavioral therapy for fibromyalgia,” Nature Clinical Practice Rheumatology, vol. 2, no. 8, pp. 416–424, 2006.
View at: Publisher Site | Google Scholar

Copyright

Copyright © 2020 Lizzette Gómez-de-Regil and Damaris F. Estrella-Castillo. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

PDF Download Citation

Download other formats

Order printed copies

Views

1892

Downloads

1247

Citations