Abstract
Objectives
Previous research suggested isolated associations of physical and psychological factors with fibromyalgia severity. Integration of physical and psychological, experienced and observed, modifiable factors associated with fibromyalgia severity in a single model will reveal therapeutic paths toward less severity of disease. We aimed to examine an encompassing model of determinants of fibromyalgia severity.
Methods
This observational, population-based cross-sectional study included 569 people with fibromyalgia. An integrative model of fibromyalgia severity was tested by using structural equation modelling. This model included 8 factors: resilience, catastrophizing, active lifestyle, declarative memory, subjective fitness, objective fitness, psychological distress, and physical fatigue.
Results
Two core paths were associated with reduced fibromyalgia severity: 1) a psychological path connecting high resilience and low catastrophizing with low distress and 2) a physical path, connecting a more active lifestyle (directly and via high objective and subjective physical fitness) with low fatigue. Additional interconnecting paths especially suggested a connection from the psychological to physical path. Our model explained 83% of the fibromyalgia severity.
Conclusions
The present model integrated the complexity of mutually influencing factors of fibromyalgia severity, which may help to better understand the disease. It emphasised the importance of: 1) physical factors and psychological factors and their interconnections, 2) patients’ experiences and clinical measurements, and 3) positive and negative signs such as physical fitness and distress. Future longitudinal and experimental research should aim at testing the causal direction of the associations in the model as well as the clinical implications suggested by the model. For instance, to reduce fatigue, exercise should enhance not only objective fitness but also fitness-related perceptions. Reducing distress and fatigue seems crucial for lowering fibromyalgia severity.
1
Introduction
Fibromyalgia is a common disease consisting of chronic widespread pain and other symptoms including fatigue, unrefreshing sleep, cognitive difficulties and somatic symptoms. It represents a serious burden that can impose significant disability. The Fibromyalgia Impact Questionnaire (FIQ), or its revised version (FIQR), is considered the gold standard for assessing fibromyalgia severity . This self-reporting instrument evaluates the previous 7-day average level of pain, energy, mental health and memory problems among other symptoms.
Fibromyalgia is poorly understood by society and healthcare professionals . Because the disease has no cure, the main aim of therapy is to reduce its severity . Therefore, identifying factors that are associated with reduced symptom burden has social, clinical and public health interest. These factors might be possible therapeutic targets if they are modifiable.
Several psychological and physical factors have been identified as potential determinants of fibromyalgia severity . Among psychological factors, particularly meaningful are those related to maintaining patients’ functioning, despite ongoing stress; namely, psychological resilience . For example, high positive affect and low pain catastrophizing are associated with low psychological distress, which in turn is related to low symptom severity . Among physical factors, engaging in physical activity is associated with reduced fatigue in fibromyalgia .
The European League Against Rheumatism has postulated that any type of pain encompasses multiple and mutually interacting factors . However, previous models of fibromyalgia severity mostly focused on isolated factors, which, from a clinical perspective, is somehow artificial. Other common caveats in the literature are the inclusion of mixed chronic pain samples (e.g., fibromyalgia and osteoarthritis analysed as a group ) or testing models that omitted physical factors (e.g., the association of psychological resilience with fibromyalgia severity ) or relied on self-reported measurements only (e.g., physical, social, and psychological factors assessed by questionnaires ). Thus, testing of more integrative models is needed, including variables assessed with a divergent method, that account for the covariance and influences between physical and psychological factors of relevance in fibromyalgia severity .
The al-Ándalus project was conducted in a large sample of individuals with fibromyalgia and included an extensive set of objective and subjective measures of physical and psychological variables that may be grouped into 8 factors ; namely, resilience, catastrophizing, active lifestyle, declarative memory, subjective fitness, objective fitness, psychological distress, and physical fatigue. Therefore, by considering the complex associations of these 8 (physical and psychological) factors within a single model, this project may provide a comprehensive picture of the determinants of (and their pathways to) fibromyalgia severity.
Fig. 1 displays 3 factors that can be targeted in treatment on the left, the overall severity of fibromyalgia on the right, and several factors that can be both maintaining factors and outcome variables in the middle. We hypothesised that, in relation to fibromyalgia severity, two pathways coexist (physical and psychological) and interplay . The physical pathway goes from active lifestyle to physical fatigue, directly and through objective (observed) and subjective (self-reported) physical fitness . In the psychological pathway, resilience and catastrophizing are related to psychological distress . Moreover, physical fatigue is associated with psychological distress . Finally, physical fatigue and psychological distress are related to fibromyalgia severity .
Several studies emphasised the importance of differentiating between objective and subjective instruments when examining determinants and health outcomes in fibromyalgia . For instance, cognitive problems are core to fibromyalgia , but a study with a small sample found no association between objectively evaluated declarative memory and fibromyalgia severity . In the present study, we expected to corroborate this lack of association between objective memory performance and fibromyalgia severity in a large sample.
This study aimed at testing a comprehensive and integrative model of fibromyalgia severity accounting for modifiable psychological and physical factors per se and their mutual influences. This model might help healthcare providers by providing a road map for reducing fibromyalgia severity. If our hypotheses are confirmed, the model may indicate that to augment the potential positive effects of pursuing an active lifestyle on reducing fatigue, both the physical performance and related appraisals (i.e., objective and subjective fitness, respectively) should be enhanced. Additionally, we would identify 3 potential pathways to lower psychological distress and consequently fibromyalgia severity, namely, to increase resilience, reduce catastrophizing or reduce physical fatigue.
2
Methods
The reporting of the paper follows STROBE guidelines ( http://www.equator-network.org/reporting-guidelines/strobe/ ).
2.1
Participants
We focused on including a representative sample of people with fibromyalgia from southern Spain (Andalusia). Participants were mostly recruited from different local fibromyalgia associations throughout the 8 provinces of Andalusia. Additional participants were recruited via e-mail, letter, telephone, and announcements in local mass media and university websites. In this observational, population-based cross-sectional study, the data collection was performed in 2 waves: the first wave was assessed between November 2011 and January 2013 and the second wave was assessed between September 2015 and September 2016. The inclusion criteria for participating in the present study were as follows: 1) a certified diagnosis of fibromyalgia by a rheumatologist and 2) current verification of fibromyalgia according to 1990 American College of Rheumatology (ACR) criteria or the modified 2011 preliminary criteria questionnaire .
All interested participants ( N = 750) gave their written informed consent after receiving detailed information about the study aims and procedures. The al-Ándalus project was reviewed and approved by the Ethics Committee of the Hospital Virgen de las Nieves (Granada, Spain) (registration number: 15/11/2013-N72). The ethical guidelines of the Declaration of Helsinki (modified in 2000) were followed.
2.2
Measures
Detailed description of the instruments are provided elsewhere . Briefly, the present study included 31 variables that according to exploratory factor analyses available elsewhere were summarised in the 8 following factors:
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resilience, which included subjective levels of emotional repair, positive affect, and optimism reported on the Trait Meta-Mood Scale (TMMS-24 ), Positive and Negative Affect Schedule , and Life Orientation Test Revised , respectively. Thus, resilience was operationalised as an umbrella term involving positive mood, emotions, and cognitions;
- •
catastrophizing, which included subjective levels of rumination, magnification, and helplessness reported on the Pain Catastrophizing Scale ;
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active lifestyle, which included objective levels (min/day) of sedentary time, light physical activity, and moderate physical activity measured by triaxial accelerometers GT3X+ (Actigraph, Pensacola, FL, USA). We have provided detailed description of this assessment previously ;
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declarative memory, which included objective levels of verbal learning, delayed recall, and recognition memory measured by performance on the Rey Auditory Verbal Learning Test (RAVLT );
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subjective fitness, which included levels of speed-agility, muscular strength, flexibility, and cardiorespiratory fitness reported on the International Fitness Scale ;
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objective fitness, which included participants’ performance in the following tests: the 30-sec arm curl, 30-sec chair stand, 6-min walk, and chair sit-and-reach tests from the Senior Fitness Test (SFT) battery ;
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psychological distress, which included subjective levels of anxiety state, negative affect, sleep quality, and depression from the State-Trait Anxiety Inventory , PANAS , Pittsburgh Sleep Quality Index , and Beck Depression Inventory-II (BDI-II ), respectively, as well as mental health and emotional role both from the Medical Outcomes Study 36-item Short Form (SF-36 );
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physical fatigue, which included subjective levels of physical fatigue, general fatigue, and reduced activity from the Multidimensional Fatigue Inventory and vitality and physical role from the SF-36 .
For the purpose of the present study, in addition to the above-mentioned factors, we included fibromyalgia severity as the outcome factor. This factor reflects the perceived levels of function, overall impact, and symptoms of fibromyalgia .
3
Procedure
Assessments were conducted over 3 consecutive days. On day 1, sociodemographic characteristics, clinical data, the BDI-II and tender point count were collected. Participants then completed several questionnaires at home, and on day 3, they returned the questionnaires and performed the RAVLT and SFT. Participants were then given an accelerometer to be worn for 9 consecutive days.
4
Statistical analyses
IBM SPSS for Windows v22.0 (Armonk, NY, USA) and Mplus v6.12 (Los Angeles, CA, USA) were used for descriptive and structural equation modelling, respectively. Before conducting the main analyses, assumptions of structural equation modelling were corroborated (see, online supplementary material ). Internal consistency and convergent validity of the variables included in the model were computed with the composite reliability (CR) and average variance extracted (AVE). CR >0.70 and AVE > 0.50 were considered acceptable; as an alternative and with CR > 0.60, AVE < 0.50 was also acceptable .
In the present study, we followed a model development strategy by using the robust maximum likelihood estimation method. The model goodness-of-fit was measured by 1) the Yuan–Bentler scaled χ2 statistic (Y–B χ2) and its degree of freedom (df) and P values, 2) the root mean square error of approximation (RMSEA) with the 90% confidence interval (CI), and 3) the Comparative Fix Index (CFI), as an incremental fit index. An acceptable model fit was defined as RMSEA < 0.07 and CFI ≥ 0.90 . Given our large sample size, we also considered the Y–B χ2/df ratio; Y–B χ2/df between 1 and 3 is deemed adequate .
5
Results
Among 750 interested participants, 89 were excluded because they did not have a previous fibromyalgia diagnosis ( N = 39) or they did not fulfill the fibromyalgia diagnosis as examined by the research team ( N = 50). Among the remaining 661 participants, 569 who completed all the assessments were included in the present study; their characteristics are in Table 1 .
| Age (years), mean (SD) | 52.1 | (8.6) |
| Sex, n (%) | ||
| Men | 32 | (5.6) |
| Women | 537 | (94.4) |
| Education level, n (%) | ||
| Unfinished studies | 128 | (22.5) |
| Primary | 247 | (43.4) |
| Secondary (and vocational) | 124 | (21.8) |
| University | 66 | (11.6) |
| Missing data | 4 | (0.7) |
| Marital status, n (%) | ||
| Married | 422 | (74.2) |
| Single | 48 | (8.4) |
| Separated/divorced | 75 | (13.2) |
| Widow(ed) | 23 | (4.0) |
| Missing data | 1 | (0.2) |
| Working status, n (%) | ||
| Working | 151 | (26.5) |
| Houseworker | 167 | (29.3) |
| Incapacity pension or sick leave | 131 | (23.0) |
| Unemployed | 92 | (16.2) |
| Others | 27 | (4.7) |
| Missing data | 1 | (0.2) |
| Fibromyalgia criteria, n (%) | ||
| Only 1990 ACR criteria | 47 | (8.2) |
| Only m-2011 criteria | 68 | (12.0) |
| Both 1990 and 2011 criteria | 454 | (79.8) |
With regard to the measurement model, Table 2 shows the factor loadings (β coefficients) of the 34 variables grouped into 9 factors and their CR and AVE values; all values were acceptable. The model goodness-of-fit was also adequate (Y–B χ2 = 1332.97, df = 491, P < 0.001; RMSEA = 0.06; CFI = 0.90; Y–B χ2 /df = 2.71).
| Measurement model | ||||||||
| Indicator variable | Factor | CR | AVE | R 2 | B | S.E. | β | |
| Emotional repair | Resilience | 0.78 | 0.54 | 0.65 | 1.19 | 0.08 | 0.81*** | |
| Positive affect | 0.54 | 1.00 | 0.73*** | |||||
| Optimism | 0.43 | 0.35 | 0.03 | 0.66*** | ||||
| Rumination | Catastrophizing | 0.91 | 0.76 | 0.72 | 1.00 | 0.85*** | ||
| Magnification | 0.69 | 0.71 | 0.03 | 0.83*** | ||||
| Helplessness | 0.88 | 1.45 | 0.05 | 0.94*** | ||||
| Sedentary behaviour | Active lifestyle | 0.80 | 0.58 | 0.85 | 1.00 | 0.92*** | ||
| Light activity | 0.60 | 0.77 | 0.06 | 0.77*** | ||||
| Moderate activity | 0.29 | 0.16 | 0.01 | 0.53*** | ||||
| Recognition memory | Declarative memory | 0.82 | 0.61 | 0.39 | 1.51 | 0.11 | 0.62*** | |
| Delayed recall | 0.65 | 1.00 | 0.81*** | |||||
| Verbal learning | 0.80 | 3.53 | 0.20 | 0.89*** | ||||
| 30-s arm curl test | Objective fitness | 0.81 | 0.52 | 0.64 | 1.48 | 0.07 | 0.80*** | |
| 30-s chair stand test | 0.73 | 1.00 | 0.86*** | |||||
| 6-min walk test | 0.47 | 20.79 | 1.32 | 0.69*** | ||||
| Chair sit-and-reach test | 0.25 | 2.19 | 0.19 | 0.50*** | ||||
| Speed agility | Subjective fitness | 0.75 | 0.44 | 0.74 | 1.27 | 0.08 | 0.86*** | |
| Muscular strength | 0.46 | 1.00 | 0.68*** | |||||
| Flexibility | 0.35 | 0.96 | 0.08 | 0.59*** | ||||
| Cardiorespiratory fitness | 0.21 | 0.71 | 0.07 | 0.46*** | ||||
| Physical fatigue | Physical fatigue | 0.77 | 0.41 | 0.48 | 1.24 | 0.09 | 0.70*** | |
| General fatigue | 0.43 | 1.00 | 0.66*** | |||||
| Vitality | 0.39 | 6.49 | 0.55 | 0.62*** | ||||
| Reduced activity | 0.33 | 1.61 | 0.18 | 0.57*** | ||||
| Physical role | 0.40 | 7.95 | 0.83 | 0.64*** | ||||
| Anxiety state | Psychological distress | 0.87 | 0.53 | 0.68 | 1.13 | 0.06 | 0.82*** | |
| Mental health | 0.64 | 1.84 | 0.10 | 0.80*** | ||||
| Negative affect | 0.56 | 0.73 | 0.04 | 0.75*** | ||||
| Emotional role | 0.46 | 2.17 | 0.13 | 0.68*** | ||||
| Depression | 0.59 | 1.00 | 0.77*** | |||||
| Sleep quality | 0.24 | 0.22 | 0.02 | 0.49*** | ||||
| Fibromyalgia function | Fibromyalgia severity | 0.81 | 0.58 | 0.50 | 1.00 | 0.71*** | ||
| Fibromyalgia overall impact | 0.54 | 0.86 | 0.05 | 0.74*** | ||||
| Fibromyalgia symptoms | 0.71 | 1.40 | 0.09 | 0.84*** | ||||
| Structural model | ||||||||
| Predictor variable | Criterion variable | B | S.E. | β | ||||
| Resilience | → | Subjective fitness | 0.03 | 0.01 | 0.26*** | |||
| Resilience | → | Physical fatigue | − 0.12 | 0.02 | − 0.36*** | |||
| Resilience | → | Psychological distress | − 0.80 | 0.10 | − 0.46*** | |||
| Resilience | → | Fibromyalgia severity | − 0.35 | 0.08 | − 0.39*** | |||
| Catastrophizing | → | Declarative memory | − 0.10 | 0.03 | − 0.16** | |||
| Catastrophizing | → | Subjective fitness | − 0.03 | 0.01 | − 0.20*** | |||
| Catastrophizing | → | Objective fitness | − 0.15 | 0.03 | − 0.21*** | |||
| Catastrophizing | → | Psychological distress | 0.88 | 0.09 | 0.39*** | |||
| Active lifestyle | → | Objective fitness | 0.01 | 0.01 | 0.12* | |||
| Active lifestyle | → | Subjective fitness | 0.01 | 0.01 | 0.16** | |||
| Active lifestyle | → | Physical fatigue | − 0.01 | 0.01 | − 0.14** | |||
| Subjective fitness | → | Objective fitness | 1.66 | 0.25 | 0.34*** | |||
| Subjective fitness | → | Physical fatigue | − 1.07 | 0.22 | − 0.35*** | |||
| Objective fitness | → | Declarative memory | 0.14 | 0.05 | 0.16** | |||
| Objective fitness | → | Physical fatigue | − 0.11 | 0.03 | − 0.17*** | |||
| Physical fatigue | → | Psychological distress | 0.85 | 0.28 | 0.17** | |||
| Physical fatigue | → | Fibromyalgia severity | 1.66 | 0.26 | 0.63*** | |||
| Psychological distress | → | Fibromyalgia severity | 0.35 | 0.04 | 0.68*** | |||
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