Pain, Emotion, and Functional Limits in Fibromyalgia
Pain, Emotion, and Functional Limits in Fibromyalgia
The study included 144 women with FM with an average age of 50 years (SD = 11). Average reported illness duration (time since diagnosis) was 18 years (SD = 13). Of the women, 81% were married, 12.1% were single, 6% divorced, and the remaining 3% were widowed. Fifty-one percent had primary studies, 21% secondary education, 12% high school education, and the remaining 16% had no studies. Twenty-nine percent were working at the time of the study, 60% were not employed, and the remaining 11% were absent from work. Of the participants, 61% used analgesics, 65% used antidepressants, and 49% used other medication (e.g., anti-inflammatories, anxiolytics, and myorelaxants) to manage FM symptoms.
Predictor Variables: Pain Dimensions. A Multidimensional Approach to the Assessment of FM Pain was Adopted, Consisting of the following Measures:
Mediating Variables. Pain Self-Efficacy was Assessed Using the Spanish Version (Martín-Aragón et al., 1999) of the Chronic Pain Self-Efficacy Scale (CPSS), a 22-Item Questionnaire Designed to Measure Chronic Pain patients' Perceived Self-Efficacy to cope with the Consequences of Chronic Pain (Anderson, Dowds, Pelletz, Edwards, & Peeters-Asdourian, 1995). the CPSS Includes Three Factors: Self-Efficacy for Pain Management, Self-Efficacy for Coping with Symptoms, and Self-Efficacy for Physical Function.
Positive and negative effects were assessed using the Spanish version (Sandín et al., 1999) of the Positive and Negative Affect Scale-PANAS (Watson, Clark, & Tellegen, 1988), a 20-item questionnaire that is composed of two factors: positive affect and negative affect (10 items for subscale).
Criterion Variables. Functional Limitation was Assessed Using the first Subscale (Physical Scale) of the Spanish Version (Esteve, Rivera, Salvat, Gracia, & Alegre, 2007) of the Fibromyalgia Impact Questionnaire (FIQ; Burckhardt, Clark, & Bennett, 1991). the FIQ Physical Scale Consists of 10 Items Assessing how FM Symptoms affect Daily Function in a Typical Week, where Higher Scores Indicate a More Negative Effect.
Anxiety and depression were assessed using the Spanish version (Herrero et al., 2003) of the Hospital Anxiety and Depression Scale (HADS; Zigmond & Snaith, 1983). The HADS is a 14-item self-report screening scale (7 items each for the anxiety and depression subscales) originally developed to indicate the possible presence of anxiety and depression in the setting of a medical nonpsychiatric outpatient clinic. Recently, Luciano, Barrada, Aguado, Osma, and Garcia-Campayo (2013)) pointed out a bifactorial structure for HADS among FM patients.
Women (ages ≥18) diagnosed with FM according to ACR criteria (Wolfe, Smythe, & Yunus, 1990) were recruited from the Fuenlabrada University Hospital, Madrid, Spain. Exclusion criteria included the existence of concomitant rheumatologic disorders, such as rheumatoid arthritis, systemic lupus erythematosus, Hashimoto's disease, Sjogren's syndrome, scleroderma, and reflex sympathetic dystrophy; and the existence of psychotic disorders, bipolar disorder, or other serious psychiatric conditions.
According to the inclusion and exclusion criteria established, patients were informed of the study and, if the patient agreed to participate, informed consent was signed. Once signed, an experienced rheumatologist from the hospital's pain unit, who was a member of the research team, confirmed the FM diagnosis by performing a physical tender point examination. The patient then was given an appointment at the fibromyalgia unit of Rey Juan Carlos University, Madrid, where a battery of tests was administered and a specialized physiotherapist performed the pressure pain sensitivity measure (algometry).
Of the 175 patients who signed the informed consent, 160 completed the rest of the measures at the fibromyalgia unit, and 144 constituted valid registers. The study protocol was approved by local Ethics Committee and conducted following the Helsinki Declaration.
To test for the presence of mediating effects, we conducted an ordinary least squares multiple regression analysis (Baron & Kenny, 1986). Several preconditions must be met to assess whether a variable has a mediating effect, establishing: (a) significant correlations between the predictor variables (pain dimensions: self-reported pain and pressure pain sensitivity) and the mediator (affect and self-efficacy); (b) significant correlations between the predictor variables and the outcome variables (anxiety, depression, and functional limitation); and, (c) significant correlations between the mediator variables and outcome variables. These preconditions were assessed with Pearson's correlations between the variables of interest.
When the preconditions have been fulfilled, the final step consists of showing that the strength of the association between pain dimensions and outcome variables is significantly reduced when the mediating variable is added to the regression model. Partial mediation is demonstrated when the beta weight for the predictor variable is reduced (but not to nonsignificance) when the proposed mediator is added to the equation. Full mediation is demonstrated if the beta value for the predictor variable is reduced from significance to nonsignificance when the proposed mediator is added to the equation (Baron & Kenny, 1986). Based on the observed correlations, we conducted hierarchical regression analyses.
Because a reduced β weight in itself does not seem to be indicative of significance, we additionally performed the Sobel test to demonstrate partial mediation (Sobel, 1982). Additionally, the relationships between sociodemographic and clinical variables (age, marital status, education level, working, years of diagnosis, years of symptoms, and medication use) and the target variables were explored by conducting the appropriate test for each variable (Pearson's correlations, t tests and one-way analysis of variances). Sociodemographic and clinical variables showing a significant relationship with the target variables were entered in step 1 of the hierarchical regression analyses.
Methods
Participants
The study included 144 women with FM with an average age of 50 years (SD = 11). Average reported illness duration (time since diagnosis) was 18 years (SD = 13). Of the women, 81% were married, 12.1% were single, 6% divorced, and the remaining 3% were widowed. Fifty-one percent had primary studies, 21% secondary education, 12% high school education, and the remaining 16% had no studies. Twenty-nine percent were working at the time of the study, 60% were not employed, and the remaining 11% were absent from work. Of the participants, 61% used analgesics, 65% used antidepressants, and 49% used other medication (e.g., anti-inflammatories, anxiolytics, and myorelaxants) to manage FM symptoms.
Instruments and Variables
Predictor Variables: Pain Dimensions. A Multidimensional Approach to the Assessment of FM Pain was Adopted, Consisting of the following Measures:
Self-reported pain was assessed with an NPS, ranging from 0 (no pain) to 10 (worst pain). The NPS has been shown to be valid and reliable in FM (Price, Patel, Robinson, & Staud, 2008). Patients were asked for their mean level of pain, the worst and the lowest level of generalized pain experienced in the preceding week. The mean score obtained from the three measures was used as a global pain score.
Pressure pain sensitivity was assessed by PPTs. PPT is defined as the minimal amount of pressure where a sensation of pressure first changes to pain (Vanderweeen, Oostendorp, Vaes, & Duquet, 1996). An electronic algometer (Somedic©, Farsta, Sweden) was used to measure PPT (kPa). The pressure was applied at a rate of 30 kPa/second. The mean score from three trials (intraexaminer reliability) was calculated and used for the main analysis. A 30-second resting period was allowed between each trial. The reliability of pressure algometry has been found to be high (intraclass correlation [ICC], 0.91; 95% confidence interval [CI], 0.82-0.97) (Vanderweeen et al., 1996). In the current study, intraexaminer reliability ranged between 0.96 and 0.98. PPT levels were bilaterally assessed over the C5-C6 zygapophyseal joint, the second metacarpal, and the tibialis anterior muscle. The order of assessment was randomized among participants. To obtain representative data about pressure pain sensitivity, a mean value of PPT was obtained for each patient.
Mediating Variables. Pain Self-Efficacy was Assessed Using the Spanish Version (Martín-Aragón et al., 1999) of the Chronic Pain Self-Efficacy Scale (CPSS), a 22-Item Questionnaire Designed to Measure Chronic Pain patients' Perceived Self-Efficacy to cope with the Consequences of Chronic Pain (Anderson, Dowds, Pelletz, Edwards, & Peeters-Asdourian, 1995). the CPSS Includes Three Factors: Self-Efficacy for Pain Management, Self-Efficacy for Coping with Symptoms, and Self-Efficacy for Physical Function.
Positive and negative effects were assessed using the Spanish version (Sandín et al., 1999) of the Positive and Negative Affect Scale-PANAS (Watson, Clark, & Tellegen, 1988), a 20-item questionnaire that is composed of two factors: positive affect and negative affect (10 items for subscale).
Criterion Variables. Functional Limitation was Assessed Using the first Subscale (Physical Scale) of the Spanish Version (Esteve, Rivera, Salvat, Gracia, & Alegre, 2007) of the Fibromyalgia Impact Questionnaire (FIQ; Burckhardt, Clark, & Bennett, 1991). the FIQ Physical Scale Consists of 10 Items Assessing how FM Symptoms affect Daily Function in a Typical Week, where Higher Scores Indicate a More Negative Effect.
Anxiety and depression were assessed using the Spanish version (Herrero et al., 2003) of the Hospital Anxiety and Depression Scale (HADS; Zigmond & Snaith, 1983). The HADS is a 14-item self-report screening scale (7 items each for the anxiety and depression subscales) originally developed to indicate the possible presence of anxiety and depression in the setting of a medical nonpsychiatric outpatient clinic. Recently, Luciano, Barrada, Aguado, Osma, and Garcia-Campayo (2013)) pointed out a bifactorial structure for HADS among FM patients.
Sampling Procedures
Women (ages ≥18) diagnosed with FM according to ACR criteria (Wolfe, Smythe, & Yunus, 1990) were recruited from the Fuenlabrada University Hospital, Madrid, Spain. Exclusion criteria included the existence of concomitant rheumatologic disorders, such as rheumatoid arthritis, systemic lupus erythematosus, Hashimoto's disease, Sjogren's syndrome, scleroderma, and reflex sympathetic dystrophy; and the existence of psychotic disorders, bipolar disorder, or other serious psychiatric conditions.
According to the inclusion and exclusion criteria established, patients were informed of the study and, if the patient agreed to participate, informed consent was signed. Once signed, an experienced rheumatologist from the hospital's pain unit, who was a member of the research team, confirmed the FM diagnosis by performing a physical tender point examination. The patient then was given an appointment at the fibromyalgia unit of Rey Juan Carlos University, Madrid, where a battery of tests was administered and a specialized physiotherapist performed the pressure pain sensitivity measure (algometry).
Of the 175 patients who signed the informed consent, 160 completed the rest of the measures at the fibromyalgia unit, and 144 constituted valid registers. The study protocol was approved by local Ethics Committee and conducted following the Helsinki Declaration.
Statistical Analysis
To test for the presence of mediating effects, we conducted an ordinary least squares multiple regression analysis (Baron & Kenny, 1986). Several preconditions must be met to assess whether a variable has a mediating effect, establishing: (a) significant correlations between the predictor variables (pain dimensions: self-reported pain and pressure pain sensitivity) and the mediator (affect and self-efficacy); (b) significant correlations between the predictor variables and the outcome variables (anxiety, depression, and functional limitation); and, (c) significant correlations between the mediator variables and outcome variables. These preconditions were assessed with Pearson's correlations between the variables of interest.
When the preconditions have been fulfilled, the final step consists of showing that the strength of the association between pain dimensions and outcome variables is significantly reduced when the mediating variable is added to the regression model. Partial mediation is demonstrated when the beta weight for the predictor variable is reduced (but not to nonsignificance) when the proposed mediator is added to the equation. Full mediation is demonstrated if the beta value for the predictor variable is reduced from significance to nonsignificance when the proposed mediator is added to the equation (Baron & Kenny, 1986). Based on the observed correlations, we conducted hierarchical regression analyses.
Because a reduced β weight in itself does not seem to be indicative of significance, we additionally performed the Sobel test to demonstrate partial mediation (Sobel, 1982). Additionally, the relationships between sociodemographic and clinical variables (age, marital status, education level, working, years of diagnosis, years of symptoms, and medication use) and the target variables were explored by conducting the appropriate test for each variable (Pearson's correlations, t tests and one-way analysis of variances). Sociodemographic and clinical variables showing a significant relationship with the target variables were entered in step 1 of the hierarchical regression analyses.
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