Clinical Phenomenology of Fibromyalgia Syndrome in male patients - Same but Different.

doi:10.21203/rs.3.rs-2586378/v1

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Clinical Phenomenology of Fibromyalgia Syndrome in male patients - Same but Different.

https://doi.org/10.21203/rs.3.rs-2586378/v1

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Background

The majority of knowledge about fibromyalgia syndrome (FMS) derives from studies of female patients. Little is known about the clinical characteristics and treatment outcomes of male FMS patients.

Objective

We investigated whether male FMS patients differ from female patients in terms of 1.) symptom burden, 2.) psychological characteristics, and 3.) clinical treatment response.

Methods

For this retrospective cohort study with a prospective posttreatment-follow-up, we identified 263 male (4%) out of 5,541 FMS patients completing a three-week multimodal pain-treatment program. Male FMS patients (51.3±9.1 years) were age- and time-matched (1:4) with female FMS patients (N = 1052, 51.3±9.0 years). Data on clinical characteristics, psychological comorbidities and treatment response were obtained from medical records and validated questionnaires.

Results

Levels of perceived pain, psychological comorbidity, and functional capacity were similar between genders, although male FMS patients showed a higher prevalence for alcohol abuse. Compared to female patients, male FMS patients experienced themselves less often as overly accommodating (Cohen’s d=-0.42), but more often as self-sacrificing (d = 0.26) or intrusive (d = 0.23). Regarding pain coping, male patients were less likely to utilize mental distraction, rest- and relaxation techniques, or counteractive activities (d = 0.18–0.27). Male FMS patients showed a slightly worse overall response rate than women (69% vs. 77%), although differences between individual outcome measures were small (d < 0.2).

Conclusion

Although male and female FMS patients in our cohort were similar in clinical presentation and treatment response, the gender-specific differences in interpersonal problems and pain coping suggest a consideration of these aspects in the treatment of male FMS patients.

Fibromyalgia

Chronic Pain

Gender

Multimodal therapy

Knowledge about fibromyalgia mostly derives from studies of female patients. Identifying and understanding gender-specific differences in fibromyalgia are an important roadmap in the treatment of this syndrome by focusing on specific gender aspects such as differences in interpersonal problems and pain coping mechanisms.

With an overall prevalence of fibromyalgia syndrome (FMS) in the general population of 2.7%, FMS is a significant health care problem. Since the occurrence is much lower in men than in women (Queiroz, 2013; Wolfe et al., 2018), current knowledge of FMS has been derived almost entirely from research with female patients. However, the perception that FMS is almost exclusively a female disorder is not confirmed by data from unbiased studies (Wolfe et al., 2018). Despite an initially assumed ratio of 9:1 female to male patients, recent estimates suggest that the proportion of men with FMS is seriously underestimated, partially due to social factors (Heidari et al., 2017; Wolfe et al., 1995). Furthermore, the knowledge about the clinical characteristics and treatment response of FMS in men is lacking. E.g., a recent systematic review identified only four studies with a sample size of > 100 male FMS patients - most of which were characterized by methodological limitations, pointing to a relevant research gap in this field (Conversano et al., 2021).

This is clinically critical, considering that numerous studies have shown that gender is an important factor in prevalence, pathophysiology and treatment response of chronic pain conditions (El-Shormilisy et al., 2015; Samulowitz et al., 2018). Literature strongly suggests gender differences not only in pain perception and the prevalence of chronic pain disorders, but also in coping with pain and the development of psychological comorbidities (Pieretti et al., 2016). Additionally, pain research demonstrated the impact of cognitive, emotional and social factors, e.g. interpersonal conflict, on the experience of pain and clinical management (King, 2021; Dailey et al., 1990). Studies have shown that high levels of stress, anxiety, and depressive symptoms, coupled with catastrophizing and interpersonal problems, are important in FMS (Bernardy, 2005).

Further studies revealed interpersonal problems as a predictor for pain catastrophizing, which stands to reason to differ between male and female FMS patients (Ryum et al., 2019). Both interpersonal and intrapersonal problems are a relevant burden in FMS, though gender-specific aspects have not yet received attention (Dailey et al., 1990; Houdenhove and Egle, 2004). However, studies in other chronic pain conditions have demonstrated gender-specific differences in interpersonal problems, e.g. male patients with irritable bowel syndrome experience more hostile-dominant behavior and less social support than female patients (Thakur et al., 2015). Similarly, gender differences have been described in chronic pain for experienced stress, prevalence of psychological comorbidities and coping behavior (El-Shormilisy et al., 2015; Keogh and Herdenfeldt, 2002; Greenspan et al., 2007). In addition, female pain patients have been shown to benefit better from a pain rehabilitation program than male patients, especially in terms of pain acceptance and comorbid anxiety levels (Pester et al., 2022). Moreover, male patients perceive their chronic pain condition and health situation as more detrimental to their social status than female FMS patients and male pain patients were shown to have a greater tendency to avoid treatment compared to female patients (Conversano et al., 2021; Zimmermann, 2002; Keogh, 2015). To date, little is known about such gender-specific differences in FMS and their impact on therapy response in male patients.

Against this background, the overall aim of this study was to clinically characterize a large cohort of male FMS patients and to investigate whether male FMS patients differ from female patients in terms of 1.) symptom burden and comorbid psychological disorders, 2.) interpersonal problems and pain coping, and 3.) their clinical response to a three-week multimodal pain therapy.

Study population and design. This study is a single-center retrospective cohort study with a prospective post-treatment follow-up at a rheumatology clinic in Baden-Baden (Germany). A total of 6,724 patients diagnosed with FMS, treated at a rheumatology clinic between 01/2004 and 03/2022 as part of a three-week multimodal pain-management program, were eligible using data from the basic documentation system of the hospital. Within this dataset, a total of N = 263 male FMS patients were identified (4%). A sample of female FMS patients was matched in a ratio of one male to four female patients (1:4) according to the treatment period (year of visit), age and number of missing entries across outcome variables (Gail et al., 1976; Lubin, 1980). All patients underwent a clinical examination at baseline, with a clinical assessment of FMS by an experienced rheumatologist. The FMS diagnosis was made according to the German guideline ACR-1990 classification criteria or the preliminary modified ACR 2010 criteria (Eich et al., 2017; Wolfe et al., 1990; Wolfe et al., 2010). The clinical diagnosis was primarily based on the history of the typical symptom complex, a clinical examination and the exclusion of physical diseases that could have adequately explained this symptom complex. The multimodal pain-management program included psychoeducation, functional training and physical therapy accompanied by treatment with medications, psychotherapy, and relaxation methods. For a detailed description of the program, see the supplementary material. This study was approved by the Ethical Board of the Heidelberg University Hospital and the executive board of ACURA clinics Baden-Baden GmbH.

Data collection. All data used in this study was approved to be used for research purposes by a written consent provided by the patients. The following sociodemographic, clinical, and psychological characteristics were assessed by a questionnaire set that all patients completed before and after the multimodal pain-management program:

Sociodemographic and clinical characteristics

Sociodemographics: Sociodemographic data was collected by the psychosomatic basis documentation questionnaire of the hospital that assessed age, gender (male/female), nationality (German/other), marital status, educational level, professional life, and intake of either pain or sleep medication, tranquilizers or antidepressants. Patients were not inquired about ethnicity or race.
Pain intensity: The intensity of perceived pain was assessed using a one-item numeric rating scale (NRS; range 0–10) of the mean intensity of the experienced “typical pain”. Higher values indicate higher perceived pain intensity.
Functional capacity: The functional capacity was assessed with the rheumatoid arthritis version of the Hannover Functional Ability Questionnaire (FFbH-R) for measuring back pain-related functional disability (Raspe et al., 1999). The final functional ability score for each patient ranged from 0 to 100% (80 to 100%: “no functional disability”, approximately 70%: “moderate disability”, and < 60%: “relevant disability”). Results from different studies indicate that the FFbH-R meets relevant psychometric criteria and sensitivity to change (Kohlmann and Raspe, 1996). The score yields an excellent reliability (Cronbach’s α = 0.90) in our study.
Fibromyalgia impact questionnaire: The severity of impact from FMS (physical functioning, work status, level of anxiety, depression, morning tiredness, pain, stiffness, fatigue, and well-being) over the last week, was assessed by the Fibromyalgia Impact Questionnaire (FIQ, range 0-100) (Burckhardt et al., 1991). Higher scores indicate a stronger impact of FMS. In studies with FMS patients, a severity analysis of the FIQ score showed mild impairment from 0 to < 39, moderate impairment from 39 to < 59, and severe effect from 59 to 100 (Bennett et al., 2009). The FIQ has been validated in patients with FMS pain and is characterized by good reliability (Cronbach’s α = 0.84) in our study (Burckhardt et al., 1991).
Quality of life: Health-related quality of life was measured by the 12-item Short Form Health Survey (SF-12) (Ware et al., 1996). The SF-12 permits the summation of individual items to yield both mental component summary (MCS) and physical component summary (PCS) scores. MCS and PCS scores are norm-based with a mean and standard deviation of 50 ± 10 and range from 0 to 100 with higher scores indicating better health status.

Psychological comorbidities

Level of depression: The level of depressive symptoms was measured by the depression module of the Patient Health Questionnaire (PHQ-dep, range 0–27) (Kroenke et al., 2001). Higher sum score are an indicator of higher depression severity. The PHQ-dep showed good reliability (Cronbach’s α = 0.84) in our study.

Additionally, the degree of change in depressive symptoms with therapy was assessed by the German version of the Center for Epidemiological Studies Depression Scale – “Allgemeine Depressionsskala” (ADS, range 0–45) (Radloff, 1977). Higher scores indicate a higher level of depressive symptoms. A good sensitivity to treatment has been shown for the ADS compared to similar instruments, and the ADS score demonstrated good reliability (Cronbach’s α = 0.89) in our study (Weiss et al., 2015).

Level of somatic symptoms: The severity of somatic symptoms was assessed by the PHQ-15 module of the Patient Health Questionnaire (PHQ-som, range 0–28 for men, and 0–30 for women) (Kroenke et al., 2002). The item regarding “pain or other problems related to the menstrual cycle” was omitted for patients with a missing entry, resulting in a total of 14 items. The sum score indicates the severity of symptom burden with higher scores indicating stronger somatic symptom severity. The PHQ-15 showed good reliability (Cronbach’s α = 0.78) in our study.
Level of stress: The level of stress was assessed using the stress-related module of the Patient Health Questionnaire (PHQ-stress, range 0–20) (Löwe et al., 2002; Gräfe et al., 2004). Using the sum score, higher values indicate more severe level of stress. The scale showed adequate reliability (Cronbach’s α = 0.76) in our study.
Psychological comorbidities: Somatoform syndrome, major depressive disorder, generalized anxiety disorder, panic disorder, bulimia nervosa, binge eating disorder and alcohol use disorder were assessed via the diagnostic modules of the PHQ (Löwe et al., 2002). The presence of comorbidities was determined via established cut-offs and categorized into “Yes”, “No” and “Possible”. The category “Possible” was assigned if a critical number of missing entries referring to a specific comorbidity was present. Overall, the questionnaire showed good validity and best operating characteristics for these comorbidities (Löwe et al., 2002).

Coping with pain and interpersonal problems

Self-efficacy: The confidence of patients in performing certain tasks focusing on pain, physical function and other symptoms was assessed by the German version of the Arthritis Self-Efficacy Scale (ASES, range 1–10) (Mueller et al., 2003). Higher scores indicate a higher confidence. The questionnaire showed good psychometric properties and evidence for construct validity in a group of FMS patients (Mueller et al., 2003). The ASES showed excellent reliability (Cronbach’s α = 0.90) in our study.
Pain coping: The utilization of pain coping strategies was assessed by the Questionnaire for pain processing and pain impairment (German acronym: FESV) (Geissner, 2001). The clinical questionnaire battery contained the first 24 items of the original 38-item questionnaire, excluding the impairment components due to the specific interest in coping mechanisms of patients at this clinic. The questionnaire yields the subscales “cognitive coping” with dimensions: action competence, cognitive restructuring, experience of competency, and the subscale “behavioral coping” with dimensions: mental distraction, countermeasures and rest and relaxation techniques. Each subscale is given on a range 4–24. Higher scores indicate a stronger utilization of the respective coping strategy (Geissner, 2001). The FESV subscales showed reliabilities ranging from acceptable to good (Cronbach’s α from 0.77 to 0.84) in our study.
Interpersonal problems: The degree of interpersonal difficulties was assessed by the Inventory of interpersonal problems (IIP-64) (Horowitz et al., 2000). The interpersonal problems were identified based on the dimensions of dominance (influencing and controlling behavior) and affiliation (non-assertiveness and submissive behavior) with interpersonal traits defined by a combination of these two dimensions. The items are grouped into eight subscales corresponding to the octants in the interpersonal circumplex: domineering/controlling, vindictive/self-centered, cold/distant, socially inhibited, non-assertive, overly accommodating, self-sacrificing and intrusive/needy. Ipsatized scores were calculated for each subscale by subtracting the mean score of all IIP items for each subscale and binning the results from 1 to 9 based on age-related norms. Higher scores indicate more interpersonal distress. The calculated reliabilities for the subscales range from acceptable to good (Cronbach’s α from 0.7 to 0.87) in our study.

Clinical treatment response

The response to the three-week pain-management program was examined using the difference between entry (pre-treatment) and discharge (post-treatment) scores. The treatment response was assessed on three different dimensions:

Changes in pain intensity (NRS), functional capacity (FFbH-R), fibromyalgia impact (FIQ) and self-efficacy (ASES)
Changes in physical and mental quality of life (SF-12: MCS and PCS, respectively)
Changes in the level of emotional distress (ADS)

Patients with a minimum improvement of 30% (moderate response) and 50% (good response) in relation to their baseline score at arrival were counted as responders.

In addition, an overall response rate was calculated based on an improvement of at least 30% in at least one of the scores described above. The percentage of responders was calculated based on the proportion of patients in each group who had completed questionnaires for each outcome score at arrival and after treatment.

Statistical analysis. The main outcome measures were the patients´ burden of symptoms (perceived pain, functional impairment, impact of FMS), presence of psychological comorbidities and their symptom severity, interpersonal difficulties, pain coping and self-efficacy, and the therapy response in the context of a three-week pain-management program. Descriptive statistics were computed stratified for the total study population as well as the male and female subgroups.

The ranked IIP-64 subscales were treated as continuous variables for the sake of comparison with other outcomes. Most variables were approximately normally distributed by visual examination of the graphically plotted distribution and QQ-plot (data now shown). Due to this and the implications of the central limit theorem for large sample sizes, the variables were treated as normally distributed. Absolute and relative frequencies were calculated for dichotomous parameters, the mean and standard deviation were calculated for continuous variables. Differences in mean outcome measures between male and female subgroups were tested by the student’s t-test and respective p-values (p_t) are reported. Cohen’s d (d) was calculated to reported effect sizes for all pairwise comparisons of continuous variables. Cohen's categories were used to evaluate the magnitude of the effect size with a d of 0.2–0.5 indicating a small effect size, d between 0.5–0.8 as a moderate effect size, and d > 0.8 as a large effect size (Cohen, 1988). The differences in mean outcome measures before and after therapy for the total, male, and female populations were calculated by paired t-tests. To test for a gender difference in the distributions of categorical outcomes, chi-square tests of independence were conducted with reported p-values (p_χ2). All p-values will be reported for the sake of completeness and as a measure of tendency in differences between genders, but no statistical significance will be discussed. No correction of p-values was conducted.

The statistical analyses described above were conducted with complete cases for each outcome measure. No obvious difference in the proportion of missing values could be observed between the male and female subgroups for the analyzed outcomes prior to sample-matching. Nevertheless, the female patients were also sample-matched based on the number of missing values (as described above), to exclude data missingness as a confounder in our analysis.

During the study period 2004–2022, only 263 out of 5,541 participants of this in-patient intensive multimodal pain-management program were male (4.7%). We included all 263 male FMS patients (age 51.3 ± 9.1 years, range 24–76 years) and 1052 matched female FMS-control patients (age 51.3 ± 9.0 years, range 20–77 years) for further analysis. The recruitment process is presented in Fig. 1.

Sociodemographic and clinical characteristics. Data on sociodemographic and clinical characteristics are presented in Table 1. Gender differences were found for information on employment, with a higher proportion of unemployed male patients (26% vs. 20%, p_χ2 < 0.001), and marital status with a lower proportion of long-term singles (10% vs. 19%, p_χ2 = 0.005) and a higher proportion of married male patients (70% vs. 61%, p_χ2 = 0.005). Regarding clinical characteristics, both male and female FMS patients were characterized by a high burden of symptoms, a high level of impairment in quality of life and functional capacity (Fig. 2a): The mean intensity of pain was NRS = 7.6 ± 1.5 and similar for both genders (male: 7.6 ± 1.5, female: 7.6 ± 1.5; p_t=0.86), thus confirming the high burden of disease of our patient cohort. The FIQ score for male and female patients was 69.5 ± 15.7 and 68.4 ± 16.8, respectively, suggesting a marked disease severity. The calculated functional capacity for both genders is at the cutoff of relevant disability with average FFBH-R values of 60.8 ± 19.0 and 58.3 ± 16.8 (p_t=0.06) for male and female FMS patients, respectively. Quality of life for both physical and mental components of SF-12 are below the healthy population mean of 50, with male FMS patients showing slightly poorer mental quality scores than female patients (33.4 ± 10.2 vs. 35.5 ± 10.5, respectively, d = 0.21, p_t=0.002). There were no differences between gender regarding educational level and medication status.

Table 1

Sociodemographic and clinical characteristics
	Total (1,315)	Male (263)	Female (1,052)
Age				p_t	d
M ± SD	51.3 ± 9.0	51.3 ± 9.1	51.3 ± 9.0	0.98	0.002
Marital status				p_χ2 0.005
No partner (short-term), N (%)	44 (3)	9 (3)	32 (3)
No partner (long-term), N (%)	234 (18)	26 (10)	198 (19)
Changing partners, N (%)	5 (0)	0 (0)	5 (0)
Long-term partner (married), N (%)	872 (63)	183 (70)	619 (61)
Long-term (not married), N (%)	225 (16)	45 (17)	163 (16)
Educational level				p_χ2 0.22
In school, N (%)	1 (0)	0 (0)	1 (0)
No school education, N (%)	39 (3)	6 (2)	33 (3)
Special school, N (%)	23 (2)	3 (1)	20 (2)
Primary school, N (%)	589 (46)	137 (52)	452 (44)
Secondary school, N (%)	445 (34)	75 (29)	370 (36)
High school, N (%)	162 (13)	32 (12)	130 (13)
Other, N (%)	35 (3)	8 (3)	27 (3)
Professional life				p_χ2 <0.001
Employed, N (%)	894 (68)	183 (70)	711 (68)
Unemployed, N (%)	275 (21)	68 (26)	207 (20)
Retirement, N (%)	74 (6)	8 (3)	66 (6)
Unknown, N (%)	72 (5)	4 (2)	68 (6)
Medications				p_χ2 0.22
No, N (%)	109 (9)	17 (7)	92 (9)
Yes, N (%)	1,172 (91)	241 (93)	931 (91)
Pain intensity, (0–10)	Total	Male	Female	p_t	d
NRS, M ± SD	7.5 ± 1.6	7.5 ± 1.6	7.5 ± 1.6	0.86	-0.01
Fibromyalgia impact, (0-100)
FIQ, M ± SD	68.6 ± 16.6	69.5 ± 15.7	68.4 ± 16.8	0.35	0.06
Functional capacity, (0-100)
FFbH-R, M ± SD	58.8 ± 19.0	60.8 ± 19.0	58.3 ± 18.8	0.06	0.13
Quality of life, (0–100)
Physical: SF-12 PCS, M ± SD	27.9 ± 7.0	27.8 ± 6.5	27.9 ± 7.1	0.69	-0.02
Mental: SF-12 MCS, M ± SD	35.1 ± 10.5	33.4 ± 10.2	35.5 ± 10.5	0.002	-0.21
p-values refer to mean differences between male and female FMS patients and are based on student’s t-test (p_t) for continuous variables and chi-squared test of independence for categorical variables (p_χ2); Cohen’s d (d) was calculated to report effect sizes for all pairwise comparisons of continuous variables; M: Mean; SD: standard deviation; N: Number of patients; %: percentage; FIQ: Fibromyalgia impact questionnaire; FFbH-R: Hannover Functional Ability Questionnaire; SF-12: Short-form 12 (Health-related quality); MCS: mental component of the SF-12; NRS: numeric rating scale; PCS: physical component of the SF-12.

Psychological comorbidities. A high level of mental comorbidities was evident in our patient cohort, with 89.8% reporting at least one mental illness (male 91.6%, female 89.3%, p_χ2 = 0.25). The prevalence of specific mental comorbidities was similar between the genders, except for alcohol use disorder, which was three times more prevalent in male than in female patients (6.5% vs. 1.7%, respectively, p_χ2 < 0.001). No noticeable difference in the severity of somatoform symptoms, perceived stress or level of emotional distress could be observed between the genders (see also Table 2).

Table 2

Psychological comorbidities (according to PHQ)
	Total	Male	Female
Somatoform syndrome				p_χ2 0.48
No, N (%)	210 (16.0)	48 (18.3)	162 (15.4)
Yes, N (%)	1,042 (79.2)	204 (77.6)	838 (79.7)
Possible, N (%)	63 (4.8)	11 (4.2)	52 (4.9)
Major depressive disorder				p_χ2 0.66
No, N (%)	676 (51.4)	129 (49.0)	547 (52.0)
Yes, N (%)	633 (48.1)	133 (50.6)	500 (47.5)
Possible, N (%)	6 (0.5)	1 (0.4)	5 (0.5)
Generalized anxiety disorder				p_χ2 0.49
No, N (%)	749 (57.0)	157 (59.7)	592 (56.3)
Yes, N (%)	520 (39.5)	99 (37.6)	421 (40.0)
Possible, N (%)	46 (3.5)	7 (2.7)	39 (3.7)
Panic disorder				p_χ2 0.45
No, N (%)	943 (71.7)	187 (71.1)	756 (71.9)
Yes, N (%)	273 (20.8)	60 (22.8)	213 (20.2)
Possible, N (%)	99 (7.5)	16 (6.1)	83 (7.9)
Bulimia nervosa				p_χ2 -*
No, N (%)	1,312 (99.8)	263 (100)	1,049 (99.7)
Yes, N (%)	0 (0)	0 (0)	0 (0)
Possible, N (%)	3 (0.2)	0 (0)	3 (0.3)
Binge-eating disorder				p_χ2 -*
No, N (%)	1,289 (98.0)	262 (99.6)	1,027 (97.6)
Yes, N (%)	0 (0)	0 (0)	0 (0)
Possible, N (%)	26 (2.0)	1 (0.4)	25 (2.4)
Alcohol use disorder				p_χ2 < 0.001
No, N (%)	1,234 (93.8)	240 (91.3)	994 (94.5)
Yes, N (%)	35 (2.7)	17 (6.5)	18 (1.7)
Possible, N (%)	46 (3.5)	6 (2.3)	40 (3.8)
Level of somatic symptoms	Total	Male	Female	p_t	d
PHQ-som, (0–30), M ± SD	17.7 ± 4.9	17.1 ± 4.7	17.9 ± 4.9	0.02	-0.17
Level of stress
PHQ-stress, (0–20), M ± SD	9.1 ± 4.5	8.6 ± 4.4	9.2 ± 4.5	0.04	-0.14
Level of depression
PHQ-dep, (0–27), M ± SD	14.5 ± 5.7	14.7 ± 5.6	14.5 ± 5.7	0.61	0.03
ADS, (0–45), M ± SD	20.2 ± 7.9	20.1 ± 7.7	20.2 ± 8.0	0.98	< 0.001
“Possible” category is assigned if a critical number of missing entries is present for items of the specific comorbidity; p-values refer to mean differences between male and female FMS patients and are based on student’s t-test (p_t) for continuous variables and chi-squared test of independence for categorical variables (p_χ2); *: chi-squared test of independence could not be conducted due to lack of entries in individual categories; Cohen’s d (d) was calculated to report effect sizes for all pairwise comparisons of continuous variables; M: Mean; SD: standard deviation; N: Number of patients; %: percentage; ADS: German version of the Center for epidemiological studies depression scale – “Allgemeine Depressionsskala”; PHQ: Patient Health Questionnaire; PHQ-som: somatic symptom severity module of PHQ; PHQ-stress: stress module of PHQ; PHQ-dep: depression module of PHQ;

Pain coping, self-efficacy, and interpersonal problems. While there were hardly any differences between male and female FMS patients regarding clinical complaints and psychological comorbidities, there were specific differences in pain coping and interpersonal difficulties. Compared to female FMS patients, male patients experience themselves less often as overly accommodating (d=-0.42, p_t<0.001), and more often as self-sacrificing (d = 0.26, p_t<0.001) and intrusive/needy (d = 0.23, p_t=0.001). In dealing with their pain, male FMS patients are less likely to report the use of mental distraction techniques (d=-0.27, p_t<0.001), rest and relaxation techniques (d=-0.19, p_t=0.006) and countermeasures (d=-0.18, p_t=0.007); see also Table 3 and Fig. 2b.

Table 3

Pain coping, self-efficacy and interpersonal problems
		Male	Female	p_t	d
Pain coping - FESV, (4–24)
Action competence, M ± SD	13.7 ± 5.3	13.5 ± 5.3	13.7 ± 5.3	0.5	-0.04
Cognitive restructuring, M ± SD	12.7 ± 5.1	12.4 ± 4.7	12.8 ± 5.2	0.26	-0.07
Experience of competency, M ± SD	13.1 ± 4.9	12.6 ± 4.7	13.2 ± 5.1	0.08	-0.11
Mental distraction, M ± SD	11.1 ± 5.1	9.9 ± 4.4	11.3 ± 5.2	< 0.001	-0.27
Rest and relaxation, M ± SD	11.8 ± 5.2	11.0 ± 4.9	12.1 ± 5.2	0.006	-0.19
Countermeasures, M ± SD	11.2 ± 5.1	10.4 ± 4.7	11.4 ± 5.2	0.007	-0.18
Self-efficacy, (1–10)
ASES, M ± SD	4.4 ± 1.8	4.3 ± 1.7	4.5 ± 1.9	0.37	-0.07
Interpersonal problems – IIP-64, (1–9)
Domineering/controlling, M ± SD	5.4 ± 1.7	5.3 ± 1.6	5.4 ± 1.7	0.46	-0.05
Vindictive/self-centered, M ± SD	6.1 ± 1.8	6.2 ± 1.7	6.1 ± 1.8	0.12	0.1
Cold/distant, M ± SD	5.7 ± 1.6	5.7 ± 1.7	5.7 ± 1.6	0.89	-0.01
Socially inhibited, M ± SD	5.5 ± 1.7	5.8 ± 1.8	5.5 ± 1.7	0.005	0.19
Non-assertive, M ± SD	5.5 ± 2.0	5.3 ± 1.9	5.5 ± 2.0	0.1	-0.11
Overly accommodating, M ± SD	5.5 ± 2.0	4.7 ± 2.0	5.6 ± 2.1	< 0.001	-0.42
Self-sacrificing, M ± SD	1.9 ± 1.1	2.1 ± 1.3	1.8 ± 1.1	< 0.001	0.26
Intrusive/needy, M ± SD	4.2 ± 1.6	4.4 ± 1.5	4.1 ± 1.6	0.001	0.23
p-values refer to mean differences between male and female FMS patients and are based on student’s t-test (p_t) for continuous variables; Cohen’s d (d) was calculated to report effect sizes for all pairwise comparisons of continuous variables; M: Mean; SD: standard deviation; %: percentage; ASES: German version of the Arthritis Self-Efficacy Scale; FESV: questionnaire for pain processing and pain impairment; IIP-64: Inventory for recording interpersonal problems.

Clinical response to treatment. An analysis of the change in symptom burden after completion of the three-week pain-management program was conducted. Overall, there were no differences between men and women in the responder rates on the different dimensions of the outcome measure. When looking for at least a 30% improvement in at least one of the outcome measures (overall response rate), there was a slight tendency for female FMS patients to respond better to therapy (69% male FMS patients vs. 77% female patients, p_χ2 = 0.008).

The tendency of a better response in women could also be seen while comparing the mean differences in outcomes scores before and after therapy. Here, a greater improvement in fibromyalgia impact (FIQ, d = 0.16, p_t=0.04) and depression scores (ADS, d = 0.19, p_t=0.009) could be observed in women compared to men (Fig. 2c and Table 4), but overall, these differences were minimal (d < 0.2).

Table 4

Differences in clinical response to treatment
	Total	Male	Female
Overall response				p_χ2 0.008
Yes, N (%)	993 (75)	182 (69)	811 (77)
No, N (%)	322 (25)	81 (31)	241 (23)
Pain intensity	Total	Male	Female	p_t	d
Difference, NRS, M ± SD	1.0 ± 1.8	0.8 ± 1.6	1.1 ± 1.9	0.19	0.10
Improvement
≥ 30.0%, N (%)	203 (22)	30 (16)	173 (24)
≥ 50.0%, N (%)	82 (9)	14 (7)	68 (9)
Fibromyalgia impact
Difference, FIQ, M ± SD	6.6 ± 18.0	4.4 ± 17.7	7.2 ± 18.0	0.04	0.16
Improvement
≥ 30.0%, N (%)	200 (22)	31 (16)	169 (23)
≥ 50.0%, N (%)	57 (6)	13 (7)	44 (6)
Functional capacity
FFbH-R, Difference, M ± SD	0.5 ± 12.0	0.6 ± 11.6	0.45 ± 12.0	0.82	-0.02
Improvement
≥ 30.0%, N (%)	98 (9)	18 (8)	80 (9)
≥ 50.0%, N (%)	47 (4)	9 (4)	38 (4)
Physical quality of life
PCS, Difference, M ± SD	-5.9 ± 11.3	-4.8 ± 10.9	-6.2 ± 11.4	0.08	-0.12
Improvement
≥ 30.0%, N (%)	417 (32)	64 (24)	353 (34)
≥ 50.0%, N (%)	275 (21)	40 (15)	235 (22)
Mental quality of life
MCS, Difference, M ± SD	-7.6 ± 12.7	-7.5 ± 12.3	-7.7 ± 12.8	0.83	-0.01
Improvement
≥ 30.0%, N (%)	489 (37)	84 (32)	405 (38)
≥ 50.0%, N (%)	311 (24)	62 (24)	249 (24)
Level of depression
ADS, Difference, M ± SD	3.8 ± 8.0	2.6 ± 7.7	4.1 ± 8.0	0.009	0.19
Improvement
≥ 30.0%, N (%)	368 (35)	60 (28)	308 (37)
≥ 50.0%, N (%)	182 (17)	29 (13)	153 (18)
Self-efficacy
ASES, Difference, M ± SD	-0.5 ± 1.8	-0.4 ± 1.6	-0.5 ± 1.9	0.49	-0.05
Improvement
≥ 30.0%, N (%)	368 (35)	60 (28)	308 (37)
≥ 50.0%, N (%)	182 (17)	29 (13)	153 (18)
“Overall response” refers to a therapy effect with an improvement of at least 30% (compared to clinic arrival) for at least one of the specified outcome scores. p-values refer to mean differences between male and female FMS patients and are based on student’s t-test (p_t) for continuous variables and chi-squared test of independence for categorical variables (p_χ2); Cohen’s d (d) was calculated to report effect sizes for all pairwise comparisons of continuous variables; M: Mean; SD: standard deviation; N: Number of patients; %: percentage indicating the fraction of responders (for 30% and 50% improvement) compared to the number of the patients that completed questionnaires at arrival and post-treatment for each outcome score for the total, male and female subgroups; ADS: German version of the Center for epidemiological studies depression scale – “Allgemeine Depressionsskala”; ASES: German version of the Arthritis Self-Efficacy Scale; FFbH-R: Hannover Functional Ability Questionnaire; FIQ: Fibromyalgia impact questionnaire; MCS: mental component of the SF-12; NRS: numeric rating scale; PCS: physical component of the SF-12; SF-12: Short-form 12 (Health-related quality).

Sensitivity analyses. A sensitivity analysis was performed to account for a potential bias in the clinical characteristics of FMS after the introduction of the preliminary modified ACR 2010 criteria towards patients with psychological comorbidities and associated psychological symptom burden. For this, the initial 5,541 patients with FMS were stratified into two groups, with the first group including patients that visited the clinic until and including 2010, and the second group comprising patients that visited from 2011 and beyond. Male patients were identified for each group (4.5% vs. 4.9%) and a sample set of female FMS patients (1:4) was matched and the datasets were analyzed according to the criteria described above. Results are presented in the supplementary material (supplementary TableS1-4). The sensitivity analysis did not show any relevant influence of the stratification on the results. No differences in the level of mental comorbidities (see supplementary TableS2) were observed. These results do not indicate any significant change in the clinical picture of FMS in this study cohort after the revision of ACR criteria.

The aim of the present study was to investigate gender differences in the presentation of symptoms and clinical response in FMS patients. For this, we compared a large cohort of male FMS patients, with an age-matched cohort of female patients, that participated in an in-patient multimodal pain-management program with respect to symptom burden, psychological comorbidity, pain coping, and interpersonal problems, as well as their treatment response. Our data shows that although the extent of perceived pain, depression, and functioning was similar between men and women, gender-specific patterns could be identified regarding interpersonal problems and pain coping. There were also only negligible differences in the presence of psychological comorbidities, except for alcohol use disorder, which was more than three-times more common in male FMS patients. In addition, men showed a slightly worse overall treatment response rate than women, although the differences between the individual outcome scores themselves were small.

The marginal gender differences in clinical presentation and incidence of psychological comorbidities are surprising. Numerous studies have shown gender differences in the occurrence of psychological comorbidities (Kessler, 2003; Jacobi et al., 2014). Consequently, one would have expected an accumulation of psychological comorbidities in female FMS patients, irrespective of the presence of FMS. This was not the case in our sample; instead, we found an overall point prevalence of 48.1% for depression and 39.5% for anxiety in our study cohort which is very high compared to the prevalence of 10% in the general population (Hajek and König, 2020). These data suggest that the presence of psychological comorbidity is a central hallmark of FMS, potentially incurring a ceiling effect masking a gender effect. This applies more to men, for whom the risk of developing unipolar depression is estimated to be only half as high as for women, with a 12-month prevalence of less than 5% in the general population (Jacobi et al., 2014). All these observations suggest that depressive symptoms are a genuine feature of FMS.

One can only speculate about the reasons for this. One explanation may be a common underlying pathomechanism that leads to the development of the FMS-characteristic pain phenotype with generalized myofascial hyperalgesia as well as psychological comorbidities. For example, it has been shown that aversive life experiences and social stressors sensitize specific neurobiological structures, which subsequently lead to the development of both generalized pain and psychological comorbidities in the sense of a "shared vulnerability model" (Asmundson et al., 2002, Tesarz et al., 2016).

The close association between FMS and psychological distress is also reflected in the 2010 revision of the ACR criteria, which shifted away from examining generalized myofascial hyperalgesia and instead relied on the assessment of pain areas and comorbid psychological symptoms (Wolfe et al., 2011). The specific inclusion of psychological symptoms in the FMS diagnostic criteria may also have led to a diagnostic bias: Clinicians might diagnose patients with generalized pain with FMS only when they report a high degree of emotional distress as well. This could also be relevant in our study, however, patients in this study sample were primarily diagnosed based on clinical assessment rather than structured evaluation of the revised ACR criteria, and a sensitivity analysis with patients included before the revision of ACR criteria did not alter the results. Although these results were surprising in some respects, they illustrate that high symptom burden and high levels of psychological distress seem to be a central characteristic of FMS – regardless of gender.

An interesting secondary finding of our study is the increased prevalence of alcohol use disorder in male FMS patients, with a three times higher rate compared to female FMS patients, although the total prevalence was very low. An association between alcohol dependence and chronic pain has been noted in the literature: Problem drinkers are more likely to report painful conditions and increased sensitivity to painful stimuli than the general population (Egli et al., 2012). It has also been noted that people with chronic pain are more likely to turn to alcohol to find relief (Riley and King, 2009), as well as moderate alcohol consumption being associated with reduced pain in chronic pain patients (Scott et al., 2018). In this respect, the increased prevalence for alcohol use disorder in male FMS patients in our study may also be evidence of the different pain coping behaviors between male and female FMS patients. However, this cannot be conclusively determined from our data and therefore remains speculative.

It is also noteworthy in this context that symptom burden and psychological distress levels showed hardly any change under three weeks of therapy. The low effects of the therapy on the clinical pain symptomatology are in accordance with the current literature: The effect sizes of both pharmacological and non-pharmacological therapies for chronic pain are generally described as low with respect to chronic pain conditions (Krebs et al., 2019; Williams et al., 2020). It should also be noted that the therapy program evaluated here was only three weeks long, which is relatively short, especially in view of the high degree of emotional distress shown by the patients.

Interestingly, our data show differences with respect to interpersonal problems and pain coping between male and female FMS patients. This is in line with the literature, which reports differences between men and women especially with regard to pain coping and social factors (El-Shormilisy et al., 2015). Both interpersonal problems and pain coping are central topics of psychological pain therapy. This suggests that even if male FMS patients hardly differ from female FMS patients in terms of symptom burden and clinical response, there are gender-specific differences in the potential content of therapy. Targeting such gender-specific aspects and perhaps even integrating them into treatment through gender-specific treatment manuals might be a useful piece of the puzzle to improve future therapies.

The following limitations of this study are important to discuss. Diagnosis confirmation was performed by an experienced clinical physician. Although this ensures high clinical validity, no standardized criteria were used. Especially among clinicians, the diagnosis of FMS is suspected when a high level of psychological comorbidity is present, whereas the diagnosis is made more cautiously in their absence. This diagnostic bias may have contributed, at least in part, to the high level of psychological comorbidity in our study sample. Another limiting factor is the restriction to a single treatment center, which is furthermore specialized in the acute care of FMS patients. Thus, our study sample represents highly distressed patients who were often in acute symptom exacerbations at the time of hospitalization. Therefore, the data of this study is certainly based on highly burdened and severely chronified patients, and not transferable to all FMS patients per se.

To conclude, the clinical picture, the level of psychological comorbidities and the functional capacity are similar between genders, but alcohol use disorder is found much more frequently in male than in female FMS patients. Overall, the treatment effects were low for both genders with small differences for each outcome measure. At the same time, there were notable differences in pain coping and interpersonal problems. Psychotherapists for pain should be aware of these gender-specific implications and adapt their approaches accordingly. This argues for developing male-specific treatment programs for FMS to overcome men's reluctance to be diagnosed and treated for FMS.

Acknowledgments

We would like to thank the ACURA-Clinics Baden-Baden GmbH for providing data on FMS patients and their outstanding scientific cooperation.

Disclosures

This work was supported by the German Research Foundation (DFG) within the Collaborative Research Center (SFB) 1158 and by the German Federal Ministry of Education and Research (Bundesministerium für Bildung und Forschung; PerPAIN consortium, FKZ:01EC1904A). No beneﬁts in any form have been or will be received from a commercial party directly or indirectly related to the subject of this manuscript. The authors have no conflicts of interest to declare. No beneﬁts in any form have been or will be received from a commercial party directly or indirectly related to the subject of this manuscript.

This study was approved by the Ethical Board of the Heidelberg University Hospital and the executive board of ACURA clinics Baden-Baden GmbH. Due to local data protection regulations, the data cannot be made freely accessible.

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Clinical Phenomenology of Fibromyalgia Syndrome in male patients - Same but Different.

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