Fibromyalgia Syndrome Pain in Men and Women: A Scoping Review

Fibromyalgia syndrome (FMS) is a chronic musculoskeletal disorder of unknown etiology that affects up to 5.0% of the world population. It has a high female predominance, between 80 and 96%. Due to the low number of diagnosed men, research work has focused mainly on women. The extensive body of literature on sex differences in pain in the general population suggests that men and women differ in their responses to pain, with greater sensitivity to pain and a higher risk of clinical pain commonly observed among women. This review aims to: (1) determine how pain is assessed or what types of questionnaires are used, (2) examine whether there are differences in pain characteristics between men and women with FMS and (3) describe how pain is conceptualized or manifested in patients at a qualitative level. In this study, the scoping review method of articles published in the last 5 years (2016–2022) was used. Ten articles were included. The most used questionnaires and scales to assess pain were the PVAS (Pain Visual Analogue Scale) and the FIQ (Fibromyalgia Impact Questionnaire). On the other hand, five categories were obtained: (1) qualities of pain, (2) uncertainty and chaos, (3) pain as an aggravating factor, (4) adaptation to the new reality and (5) the communication of pain. It has been observed that both subjective perception and widespread pain are higher in women. Men, on the other hand, have a worse impact of the pathology, more painful experiences and more catastrophic thoughts about pain. An updated knowledge of pain in FMS and whether it differs according to sex would be beneficial for clinicians to make an earlier diagnosis and treatment and, in turn, benefit patients suffering from this chronic disease.


Introduction
Fibromyalgia syndrome (FMS) is a chronic musculoskeletal disorder of unknown etiology that affects up to 5.0% of the world's population [1,2]. The incidence is greater in Europe (2.64%) than in America (2.41%) or parts of Asia (1.62%) [3]. The percentages fluctuate from country to country because the ways of determining them are diverse, as are the age groups included and the differentiations in sociocultural standards. Consequently, for example, the prevalence in Spain is about 2.4%, while in the USA it is 2% [4]. This pathology greatly alters individual health-related quality of life. The vast bulk of affected people end up suffering from diverse kinds of disability, isolation, stigmatization, lack of validity of their diagnosis and concern about their long-term prognostication [5].
Fibromyalgia syndrome has a high female predominance, accounting for 80-96% [4,6]. Still, a systematic review of FMS in men and women worldwide described that the predominance of the condition is similar for both sexes, i.e., approximately 3.98% in women and 2.40% in men [7]. Due to the low number of diagnosed men, research has mainly focused on women, ignoring the study of this syndrome in men. The difference between men and women in the prevalence and diagnosis of FMS appears to be related to the social stigma related with it being a mostly female illness and to the social and cultural characteristics of Western countries, where men are less likely to go to a specialist for chronic pain symptoms, which limits the formulation of a correct diagnosis [8,9].
The extensive body of the literature on sex disparities in pain in the general population strongly suggests that men and women differ in their responses to pain, with greater pain sensitivity and higher risk of clinical pain commonly observed among women [10,11]. Thus, the idea of sex differences in FMS symptoms gains clarity. If women and men with FMS present with a different impact and intensity of symptoms, it would be advisable to diagnose and treat on an individualized basis.
Fibromyalgia syndrome presents with a wide variety of signs and symptoms, making it difficult to diagnose. So far, there are no biomarkers of the disease and clinical evaluation and patient descriptions are used. Continuous efforts have been made to improve the diagnostic accuracy of FMS [12]. The 2016 American College of Rheumatology criteria are the most accurate and used in clinical practice. According to the Wolfe et al. definition, FMS is a condition that involves widespread pain in at least four of five regions (left upper region, right upper region, left lower region, right lower region, axial region) and the symptoms must have been present for at least 3 months. Also, the widespread pain index (WPI) must be equal to or greater than seven and the symptom severity scale (SSS) score must be equal to or greater than five. Alternatively, the integrated pain management (IPM) must be between four and six and the SSS score must be equal to or greater than nine. Furthermore, the diagnosis is valid independently of other diagnoses; i.e., FMS does not exclude the presence of other clinically important diseases [13].
As for treatment, it is not curative, and its aim is to reduce symptoms in order to provide greater functionality to the person [14]. As it is a very complex condition, all authors conclude that the treatment of FMS should be holistic, comprehensive and with a multidisciplinary approach [15].
Pain is the central symptom of FMS, which coexists with many other symptoms such as fatigue, insomnia, cognitive dysfunction and mental health disorders [16]. Fibromyalgia syndrome pain is defined as chronic, meaning that it persists or recurs for more than three months [17]. It mainly affects the musculoskeletal system and is present throughout the body, from the head to the feet [18]. Usually, initially the pain is localized, but over time it affects many muscle groups. It is characterized by being persistent with variable intensity, while it can often be described as a burning sensation or stabbing pain. There is oversensitivity to normally painful stimuli, such as pressure or heat (hyperalgesia) and painful sensation to normally non-painful stimuli, such as touch (allodynia) [19].
The fact that FMS presents chronic pain without any obvious peripheral tissue damage has given rise in recent years to the new concept of nondisciplastic pain, also known as nocioperception, which comes from the Latin nocere: pain that activates peripheral nociceptors without clear evidence of actual or threatening tissue damage.
The type, location and severity of pain depend on several modulating factors, the most important of which are physical exercise, comorbidities such as obesity and temperature variations [20].
The present scoping review has focused the study of pain in men and women in FMS. Considering that it is a disabling symptom that is present daily in people with FMS, we believe that it is of vital importance to find out its characteristics known to date and thus be able to provide a more updated view to clinicians (especially in Primary Care) to provide earlier diagnosis and treatment and, in turn, benefit patients suffering from this chronic disease.
Our aims focused on: (1) determining how pain is assessed or what types of questionnaires are used, (2) examining whether there are differences in pain characteristics between men and women with FMS and (3) describing how pain is conceptualized or manifested in the participants at a qualitative level.

Materials and Methods
This scoping review was undertaken in line with the Preferred Reporting Items for Systematic Reviews (PRISMA) guidelines for scoping reviews [21]. The Preferred Reporting Items for Scoping Reviews (PRISMA-ScR) Checklist can be found in Appendix A.

Inclusion Criteria
The identified studies were subjected to inclusion and exclusion criteria. To be included, studies had to be published from January 2016 to July 2022, available in full text, written in English or Spanish and use both quantitative (observational studies) and qualitative methodology. Clinical trials, case studies, opinion articles, interventions, or systematic reviews (with or without meta-analysis) were excluded to ensure higher quality evidence.

Search Strategy
The bibliographic search was carried out during the months of February and July 2022. The electronic databases used for the search were PubMed, SCOPUS, CINAHL, Web of Science and Google Scholar. In each of these, an exhaustive search was performed using a combination of Boolean logic and truncations for the following keywords: "pain", "fibromyalgia", "men", "women", "conceptualization", "manifestation", "score" and "assessment".
The following search string was used for SCOPUS: (fibromyalgia) AND (pain) AND (men OR women) AND (score OR manifestation OR concept* OR assessment). For the PubMed database, we used (((("Fibromyalgia"(Mesh)) AND "Pain"(Mesh)) AND "Men"(Mesh)) OR "Women"(Mesh)) OR ("Pain Measurement/classification"(Mesh) OR "Pain Measurement/instrumentation"(Mesh) OR "Pain Measurement/nursing"(Mesh) OR "Pain Measurement/psychology"(Mesh)) OR (score) OR (concept*) OR (manifestation) OR (assessment). For the CINAHL, Web of Science and Google Scholar Boolean we used the terms fibromyalgia AND pain AND (men OR women) AND (score OR manifestation OR concept* OR assessment. The complete search strategy is illustrated in Figure 1.

Selection of the Studies
The studies obtained were imported and processed using the bibliographic reference management software Mendeley Desktop ® version 1.19.4 (London, UK).
The selection process consisted of two levels of screening of the articles obtained: (1) a review of the title and abstract and (2) a review of the full text.
The articles retrieved by the database search were evaluated by the PhD supervisor, who made the evaluation by reading the title and abstract provided by the PhD student. The previous authors also read the full texts of all publications that could not be excluded at the title/abstract level. They reviewed the abstracts/titles of the articles and agreed on which met the inclusion/exclusion criteria for full-text review. Disagreements about study selection and data extraction were resolved by consensus by the majority of the authors of the present review or by using an external author [22].

Data Extraction
Data were extracted from full-text articles that met the objectives and inclusion criteria. Definitive data were obtained using a data extraction form with the following information: author(s), year of publication, country, study design, study objective(s), participants (sex and age range). In the case of quantitative studies, the types of questionnaires used were also considered. In the qualitative articles, for the review of the experiences of men and women with FMS, the authors proceeded to analyze the discourses related to the conceptualization or manifestation of pain by means of categories and subcategories.

Process Followed to Determine the Categories and Subcategories of Pain in the Qualitative Studies
We progressed with two phases to obtain and show the presence in the verbal explanations and experiences of people with FMS of the categories and possible subcategories in each study: (1) statements, responses, individual or group aspects related to pain were identified; (2) after having recognized the categories, a second in-depth analysis was carried out that allowed us to get subcategories and to be able to catalogue them [23].

Results
Our search strategy resulted in a total of 10 final references after the selection process, as can be seen in Figure 1.

Data Extraction
Data were extracted from full-text articles that met the objectives and inclusion criteria. Definitive data were obtained using a data extraction form with the following information: author(s), year of publication, country, study design, study objective(s), participants (sex and age range). In the case of quantitative studies, the types of questionnaires used were also considered. In the qualitative articles, for the review of the experiences of men and women with FMS, the authors proceeded to analyze the discourses related to the conceptualization or manifestation of pain by means of categories and subcategories.

Process Followed to Determine the Categories and Subcategories of Pain in the Qualitative Studies
We progressed with two phases to obtain and show the presence in the verbal explanations and experiences of people with FMS of the categories and possible subcategories in each study: (1) statements, responses, individual or group aspects related to pain were identified; (2) after having recognized the categories, a second in-depth analysis was carried out that allowed us to get subcategories and to be able to catalogue them [23].

Results
Our search strategy resulted in a total of 10 final references after the selection process, as can be seen in Figure 1. All selected studies with their main results are shown in Table 1. All selected studies with their main results are shown in Table 1.
Pain Visual Analogue Scale (0-10) Higher values of pain and symptom severity were detected in women relative to men. Since FMS is defined based on pain and symptom severity, women will always be more likely to be diagnosed. In short, there is a relationship between being female and being diagnosed with FMS. Comparative Cross-Sectional Study Quantitative To characterize childhood experiences, perceived lack of parental affection, hypersensitivity to stimuli, life stressors, anxio-depression and ergomania.

Quantitative
To assess the pain pressure thresholds (PPT) and subjective pain perception (SPP) of the 18 PTs while applying standardized pressure.

Focus groups and interviews
• Common experiences (Spanish and American) include fluctuating pain (especially with movement), pain considered invisible to others and localized pain. • Pain triggers, such as thermosensitivity.
Physical exertion, such as walking. Both samples acknowledged that the more they moved, the more pain they experienced. Of the 10 studies that met the inclusion criteria, 7 were quantitative [1,[24][25][26][27][28][29], 2 qualitative [16,31] and 1 mixed (qualitative methodology together with quantitative methodology) [30]. Sample sizes ranged from 5 to 4342 participants. The sum of all participants with FMS from the studies was 5222 (2262 males and 2960 females); of these, the female sex predominated with 56.7%. In all studies, the age range was 18 years or older; older subjects had a mean age of 56.6 ± 12.6 years.
The predominant countries were Spain with three studies [24,28,30] and the United States with two [25,30]. The study by Kueny et al. was performed in two different countries, Spain and the United States, with the aim of being able to observe pain in different cultural contexts [30]. The patients came from the United States [25,30], Spain [24,27,29,31], Finland [16], France [27], Thailand [26], China [1] and Italy [29]. The Spanish study by Sendra and Farré contained patients from all over the world, as they worked with the Instagram social network [31].
The pain assessment of the selected quantitative studies included a wide variety of questionnaires and scales ( Table 2)    For this study, the total score (ranging from 0 to 52) was used, where higher score represents a more negative appraisal of pain [24].  On the other hand, qualitative studies used tools such as focus groups, interviews and narrative and life history to describe how pain manifests itself in men and women with FMS.
The PVAS and WPI were higher in female participants [1,25,29]. In Wolfe's study, males were older (64.9 ± 12.0 years) than females (59.7 ± 13.5 years) [25]. In contrast, in the Jiao study men were significantly younger p = 0.027 (43.6 years) than women (50.1 years) [1]. The FIQ and PCS were somewhat higher in men than in women in the Segura-Jiménez study, [24] but without statistical significance. There were no differences for the rest of the scales.
The review of the qualitative literature allowed us to detect the presence of categories related to pain. A total of five categories were obtained: (1) qualities of pain, (2) uncertainty and chaos, (3) pain as an aggravating factor, (4) adaptation to the new reality and (5) communication of pain.
In the first category-pain qualities-we integrated the results associated to the pain characteristics reported by patients in the chosen studies. The second category-uncertainty and chaos-describes how patients cope with chronic pain. The third category-pain as an aggravating factor-reflects the different causes of chronic pain in patients. In the fourth category-adaptation to the new reality-we show how patients make vital changes to continue living with pain. Finally, in the last category-pain communication-we show the importance of expressing emotions and sharing the experience of pain as a benefit for the person.

Pain Qualities
In the study by Sallinen and Mengshoel men affected by FMS vividly described their pain with fluctuating intensity from day to day [16]. On good days the pain was almost non-existent, but on bad days it could become agonizing. On the other hand, the male participants in Kueny's study also described the pain as excruciating, a "pain [through] the soul". Yet, their worst pain was reported as shooting and location-specific rather than being described as widespread or generalized as we are accustomed to reading about in fibromyalgia patients [30].

Uncertainty and Chaos
The patients in the Sendra and Farré study manifest continuous uncertainty when suffering from an incurable disease that manifests with chronic pain. Everyday actions become major obstacles [31]. Since this pathology is sometimes difficult to diagnose, most patients used narratives of chaos to talk about their chronic pain. They feel they are losing control of their lives and, at the same time, this loss of control ends up affecting their identity. These patients mostly reflect that they do not perceive a positive evolution of their health, although a small percentage are confident about their future despite all their problems. In the context of this disease, the existence of this duality is manifested in chronic diseases as they tend to oscillate between periods of exacerbation, in which symptoms such as pain worsen, and periods of quiescence, in which disability is less disturbing.
If we focus only on male patients, this uncertainty also manifests itself; Kueny described that men were surprised by the sporadic nature of their pain, a constant pain that is ever present in their lives and makes it difficult for them to make plans [30].

Pain as an Aggravating Factor
Selected studies show that patients are not only threatened by fibromyalgia pain but also by the pain as an aggravator of other symptoms [16,30]. Patients describe problems falling asleep, which in turn causes tiredness and daytime fatigue [30]. Pain and their lack of energy limit them in all levels of their social relationships [31]. They describe having changes in their personality, feeling more irritable with others and even being disappointed with themselves for not being able to fulfil their roles as they would like or as they did before [30].
According to Sendra and Farré, patients with chronic pain end up isolated and stigmatized, as presenting "invisible pain" causes them emotional distress by having to repeatedly demonstrate their disability to others, both people close to them and healthcare professionals [31]. The study by Kueny also reflects how difficult the invisible nature of the pain they experience is for their patients and they also acknowledged having to be their own advocates in the face of others who did not believe them [30].

Adaptations to the New Reality
People suffering from chronic pain tend to seek a balance between health and illness, between ability and disability [16]. According to the selected qualitative studies, patients tend to look for which are the aggravating factors of their pain in order to decrease or eliminate them; for example, with physical exertion such as walking, patients explained that the more they moved, the more pain they experienced; consequently, they had to manage their body movements well during the day [30]. Patients expressed having to make major changes in their lives in order to "live with their pain": changes in work, role, personal life, family, routines, etc. [31].

Communication of Pain
The previous categories reflect how chronic pain causes drastic changes in the lives of people who suffer from it, and although pain is presented as the main enemy of these people, studies reflect that it is vitally important to talk about it. Sendra and Farré suggest that sharing the experience is very beneficial, either self-reported, i.e., verbally, or with the help of assessment tools. It should be kept in mind that suffering chronic pain is a recurrent experience with clearly emotional components that have to be drained in an individualized way for the biopsychosocial well-being of the person [31].

Discussion
This review provides an updated synthesis of fibromyalgia pain from different approaches to better understand it.
As for the way in which pain has been assessed, the results show that the PVAS (which assesses the subjective perception of global pain) and the FIQ (which assesses the impact of illness) were the most used tools. Despite this, we believe that the consideration of the PVAS in terms of its structure and the patient's behavior on the scale casts doubt on its validity. It is linear and is prone to biases; for these reasons, we consider that its use should be limited. On the other hand, we are confident in the use of the FIQ, as it assesses the status, progress and prognosis of patients and is an instrument that is extensively used in the healthcare setting [32].
We contrasted whether there were differences in pain characteristics according to sex. We detected that the subjective perception of pain was higher in women, as was the generalized pain index (WPI). In contrast, FMS impact was higher in men, as were painful experiences and PCS pain thoughts. The worst Pain Visual Analogue Scale scores are obtained by women both in studies analyzing only women [27,28] and in studies studying men and women [1,25,29]. The worst FIQ scores are those obtained by Kueny in male patients with FMS [30]. In Ubeda-D'Ocasar's study only with women, the highest PVAS values were present in the supraspinatus muscle, the trochanteric prominence and the upper outer quadrant of the buttocks, respectively [28].
Wolfe's study with men and women exposed low PVAS values in both sexes and no significant differences [25]. The Chinese study by Jiao also did not detect significant differences between the PVAS of their men and women [1]. In contrast, the mixed study by Iannuccelli showed high PVAS values in women with statistical significance [29], although it should be noted that in all three studies the representation of men with respect to women was very low.
The FIQ values in the mixed study by Segura-Jiménez [24] were elevated, but there were no significant differences among men and women with FMS. In contrast, in the Italian study by Iannucceli, women had higher FIQ values than men [29]. Úbeda-D'Ocasar's study [28] only with women (n = 30 W) also presented high values with the FIQ, although, the values were higher in the male study (n = 17 M) by Kueny and colleagues. The FIQ was also compared by country (USA or Spain) to detect whether there were cultural contrasts in different health policies. Spanish men had higher values, but the differences only approached statistical significance. Demographic factors do not directly influence pain perception but represent valuable individual difference factors [30]. Although several examples of epidemiological evidence have shown that chronic pain conditions are more predominant among women than among men, [35,36] in our review we only detected this in Jiao's study, which revealed significant differences in pain according to sex. Women with FMS had worse values in the WPI questionnaire (generalized pain) and men with FMS had worse values in the SSS (severity of symptoms) [1].
Finally, through the use of qualitative methodology this review wanted to describe how pain is conceptualized or manifested in affected individuals. Pain, according to male participants in the studies by Sallinen and Mengshoel [16] and Kueny, has qualities of being fluctuating. Also, agonizing and unbearable at the worst times. Unlike other studies, the pain of the men in Kueny et al. is of a localized type, not generalized and has a stabbing characteristic, such as by an arrow or sword [30]. According to Ruschak's study, the pain of men with FMS was also described as "like an arrow or heart attack" and of a fluctuating type; i.e., it was present in different sections of the body, not generalized [37]. The chronicity and random nature of fibromyalgia pain causes much uncertainty and chaos in the lives of these patients [30,31]. Fatigue and insomnia also entail major problems in their lives, which are closely linked to pain, which is their direct aggravating factor [30], a phenomenon also shared in the study of Ruschak et al. [37]. These in turn also limit them at all levels of their social relationships [30,31] because the invisible nature of pain means that patients have to be their own advocates in front of others, because they do not believe them. These challenging situations full of negative attitudes have been previously described in other studies on FMS [9,[37][38][39]. According to Ruschak and colleagues, the lack of understanding shown by some clinicians, as well as their family and friends, has had a very bad impact on patients' health, principally psychological health [37]. Sallinen suggests that there is also a consequence for their identity, especially their masculinity, as it has had to be renegotiated and reconstructed [16]. All these changes in their lives are difficult to face, but necessary. Acceptance of the new reality helps people to move on, mainly with the help of others. This help begins with communicating their discomfort and finding a receptive listener so that they can talk about their pain [40].

Conclusions
The results of this review provide updated information on FMS pain in both sexes. To date, we can see that pain remains a very complex, internal and private sensory experience and more so in men because FMS is still mostly conceptualized as a women's disease.
It has been observed in a few studies that both subjective perception and the generalized pain index are higher for women, but a worse impact, more painful and more severe experiences, and also more catastrophic thoughts about pain in men should be considered. In any case, the results have little statistical significance, and we consider that it is necessary to increase the sample of men in the studies so that these particularities can be studied in greater depth.
To improve pain care in these patients, we believe that there is a need for multidisciplinary management including educational interventions aimed at health care personnel on the diverse concepts of pain (subjective perception, impact of pain, widespread pain, localized pain, severity of symptoms, catastrophic thoughts about pain), to thus help to improve the understanding of individual and gender disparities in pain.
The results of this review have been made possible by the increasing inclusion of men with FMS and the awareness that the male experience and perspective is just as important as the female. Even so, we encourage further expansion of the male sample in future studies, because with the current results the significative differences in male and female pain did not reach statistical significance in all the studies, probably due to the small sample of men.

Limitations
Some limitations must be mentioned. First, reducing the review to the last 5 years allowed us to identify that there are fewer studies than we thought related to the subject. Secondly, in the mixed studies, the proportion of men to women is unbalanced and the low male representation is detrimental to them and limits their perspective. Finally, there are biases in some regions and we detected that there are countries in which FMS is not studied as much, for example Asian countries. This is probably due to the type of healthcare access they have or their cultural beliefs.
In short, FMS remains an area that needs more awareness and investigation by researchers. Funding: This research received no external funding.

Institutional Review Board Statement: Not applicable.
Informed Consent Statement: Not applicable.

Data Availability Statement:
No new data were created or analyzed in this study. Data sharing is not applicable to this article.

Conflicts of Interest:
The authors declare no conflict of interest.
Appendix A Table A1. Preferred Reporting Items for Systematic reviews and Meta-Analyses extension for Scoping Reviews (PRISMA-ScR) Checklist. To obtain higher quality results, it is essential to increase the sample of men with FMS in future studies in order to be able to deepen these differences. The choice of the scoping review was mainly due to the heterogeneous nature of FMS in existing studies to date. The scoping review allows us to better group the literature according to its characteristics.

Objectives 4
The present review has focused the study of pain in men and women in FMS. Our objectives focused on (1) determining how pain is assessed or what types of questionnaires are used, (2) examining whether there are differences in pain characteristics between men and women with FMS and (3) describing how pain is conceptualized or manifested in the participants at a qualitative level. 3

Protocol and registration 5
Not applicable. The review protocol is in the process of being accepted by PROSPERO: www.crd.york.ac.uk/prospero/, accessed on 10 November 2022

Eligibility criteria 6
The identified studies were subjected to inclusion and exclusion criteria. To be included, studies had to be published from January 2016 to July 2022, available in full text, written in English or Spanish and use both quantitative (observational studies) and qualitative methodology. 3

Information sources 7
The bibliographic search was carried out during the months of February and July 2022. The electronic databases used for the search were PubMed, SCOPUS, CINAHL, Web of Science and Google Scholar. In each of these, an exhaustive search was performed using a combination of Boolean logic and truncations for the following keywords: "pain", "fibromyalgia", "men", "women", "conceptualization", "manifestation", "score" and "assessment". 3

9
The electronic databases selected for the search were PubMed, SCOPUS, CINAHL, Web of Science and Google Scholar. 3

Data charting process 10
Data were extracted from full-text articles that met the objectives and inclusion criteria. Definitive data were obtained using a data extraction form with the following information: author(s), year of publication, country, study design, study objective(s), participants (sex and age range). In the case of quantitative studies, the types of questionnaires used were also considered. In the qualitative articles, for the review of the experiences of men and women with FMS, the authors proceeded to analyze the discourses related to the conceptualization or manifestation of pain by means of categories and subcategories. 4

Selection of sources of evidence
12 Figure 1 4 Table A1. Cont.

Synthesis of results 13
Of the 10 studies that met the inclusion criteria, 7 were quantitative, 2 qualitative and 1 mixed. Sample sizes ranged from 5 to 4.342 participants. The female sex predominated with 56.7%. In all studies, the age range was 18 years or older; older subjects had a mean age of 56.6 ± 12.6 years. The pain assessment of the selected quantitative studies included a wide variety of questionnaires and scales. The most used were the PVAS (out of 10 or out of 100) and the FIQ. On the other hand, qualitative studies used tools such as focus groups, interviews, narrative and life history to describe how pain manifests itself in men and women with FMS. The PVAS and WPI were higher in female participants. In Wolfe's study, males were older (64.9 ± 12.0 years) than females (59.7 ± 13.5 years). In contrast, in the Jiao study men were significantly younger p = 0.027 (43.6 years) than women (50.1 years). The FIQ and PCS were somewhat higher in men than in women in the Segura-Jiménez study, but without statistical significance. There were no differences for the rest of the scales.
The review of the qualitative literature allowed us to identify the existence of categories related to pain. A total of five categories were obtained: (1) qualities of pain, (2) uncertainty and chaos, (3) pain as an aggravating factor, (4) adaptation to the new reality and (5) communication of pain.
In the first category-pain qualities-we integrated the results related to the pain characteristics reported by patients in the chosen studies. The second category-uncertainty and chaos-describes how patients cope with chronic pain.
The third category-pain as an aggravating factor-reflects the different causes of chronic pain in patients. In the fourth category-adaptation to the new reality-we show how patients make vital changes to continue living with pain. Finally, in the last category-pain communication-we show the importance of expressing emotions and sharing the experience of pain as a benefit for the person. Table A1. Cont.

Summary of evidence 14
This review provides an updated synthesis of fibromyalgia pain from different approaches to better understand it. The first objective of this review was to determine how pain is assessed, i.e., which questionnaires are commonly used. The results show that the PVAS (which assesses the subjective perception of global pain) and the FIQ (which assesses the impact of illness) were the most used tools. We contrasted whether there were differences in pain characteristics according to sex. We detected that the subjective perception of pain was higher in women, as was the generalized pain index (WPI). In contrast, FMS impact was higher in men as were painful experiences and PCS pain thoughts.
Although several examples of epidemiological evidence have shown that chronic pain conditions are more prevalent among women than among men, in our review we only detected this in Jiao's study, which revealed significant differences in pain according to sex. Women with FMS had worse values in the WPI questionnaire (generalized pain) and men with FMS had worse values in the SSS (severity of symptoms). Finally, through the use of qualitative methodology this review wanted to describe how pain is conceptualized or manifested in affected individuals. Pain, according to male participants in the studies by Sallinen and Mengshoel and Kueny, has qualities of being fluctuating. Also, agonizing and unbearable at the worst times. Unlike other studies, the pain of the men in Kueny et al. is of a localized type, not generalized and has a stabbing characteristic such as an arrow or sword. According to Ruschak's study, the pain of men with FMS was also described as "like an arrow or heart attack" and of a fluctuating type; i.e., it was present in different parts of the body, not generalized. The chronicity and random nature of fibromyalgia pain causes much uncertainty and chaos in the lives of these patients. Fatigue and insomnia also entail major problems in their lives, which are closely linked to pain, which is their direct aggravating factor, a phenomenon also shared by the study of Ruschak et al. These in turn also limit them at all levels of their social relationships because the invisible nature of pain means that patients have to be their own advocates in front of others, because they do not believe them. These challenging situations full of negative attitudes have been previously described in other studies on FMS. According to Ruschak and colleagues, the lack of empathy shown by some healthcare professionals, as well as their family and friends, have had a very negative impact on patients' health, especially mental health. Sallinen suggests that there is also a consequence on their identity, especially their masculinity, as it has to be renegotiated and reconstructed. All these changes in their lives are difficult to face, but necessary. Acceptance of the new reality helps people to move on, mainly with the help of others. This help begins with communicating their discomfort and finding a receptive listener so that they can talk about their pain.

12-13
Limitations 15 Some limitations must be mentioned. First, reducing the review to the last 5 years has led us to identify that there are fewer studies than we thought related to the subject. Secondly, in most of the mixed studies, the proportion of men to women is unbalanced; the low male representation is detrimental to them and limits their perspective. Finally, there are biases in some regions; we detected that there are countries in which FMS is not studied as much, for example Asian countries. This is probably due to the type of healthcare access they have or their cultural beliefs. In short, FMS remains an area that needs more awareness and investigation by researchers. The results of this review provide updated information on FMS pain in both sexes. To date, we can see that pain remains a very complex, internal and private sensory experience and more so in men because FMS is still mostly conceptualized as a women's disease. It has been observed in a few studies that both subjective perception and the generalized pain index are higher for women, but a worse impact, more painful and more severe experiences and also more catastrophic thoughts about pain in men should be considered. In any case, the results have little statistical significance and we consider that it is necessary to increase the sample of men in the studies so that these differences can be studied in greater depth.
To improve pain care in these patients, we believe that there is a need for multidisciplinary management including educational interventions aimed at health care personnel on the different concepts of pain (subjective perception, impact of pain, widespread pain, localized pain, severity of symptoms, catastrophic thoughts about pain) to thus help to improve the understanding of individual and gender differences in pain.
The results of this review have been made possible by the increasing inclusion of men with FMS and the awareness that the male experience and perspective is just as important as the female. Even so, we encourage further expansion of the male sample in future studies, because with the current results the significative differences in male and female pain did not reach statistical significance in all studies, probably due to the small sample of men. 13