Study design
A longitudinal cohort study.
Patients and methods
Participants
In the year of 2004–2005, 166 women with FM or CWP recruited in primary care in western Sweden participated in a randomized controlled trial (RCT) called the GAU-study, comparing a patient education program in combination with 20 weeks of pool exercise with a control group participating in a patient education program as only treatment [17]. All participants completed a battery of questionnaires regarding symptoms and health and performed tests of physical function at baseline. The impact of a 20 week intervention was considered to be negligible after 10 to 12 years, thus the whole cohort of 166 women were eligible for recruitment in the present follow-up of natural course of symptoms over time.
Inclusion criteria
The 166 women with FM or CWP who participated in the baseline examination of the GAU study 2004–2005 [17] were invited to participate in the present study. The inclusion criteria of the GAU study [3] were women with FM or CWP, in the age range 18–60 years. CWP was classified as pain above and below the waist, at the right and left side of the body and axial pain for at least 3 months. FM was classified as having CWP in combination with pain at manual palpation at 11 out of a total of 18 examined tender-point localizations [3]. The exclusion criteria of the GAU-study 2004–2005 were other severe somatic or psychiatric disorders or ongoing exercise therapy supervised by a physical therapist [3].
Exclusion criteria
Participants who had deceased, or developed serious physical or psychological disease since they were included in the GAU-study, such as cancer during treatment, stroke with severe physical impairment or schizophrenia.
Recruitment
All 166 women received a letter with information about the present study, except four participants who were deceased. The letter was followed up for the 162 participants by telephone for more information about the study and invitation to participate. Those who could not be reached by phone received a second letter with inquiry about new contact information. Eight persons were excluded during the phone call according to exclusion criteria, and 19 declined to participate. Nine could not be reached. A final total of 126 women (76%) participated in the present follow-up.
Data collection
Procedure
The examinations were performed by trained physical therapists who were blinded to previous baseline test results. The examinations took place at rehabilitation centers in the three cities Göteborg, Alingsås and Uddevalla in western Sweden, from April to December 2016. The same measurements that were used at baseline were included in the follow-up examination which lasted about 1.5 h and included a battery of questionnaires, physical examination of tender points [3] and tests of physical function and a standardized interview with questions about duration of pain, employment status, sick leave and disability pension, education, marital status, concomitant disorders and medications.
Background data
Employment was divided into four categories referring to percentage of full time work, which is defined as 40 h per week.
Sick leave and Disability pension were categorised as 0, 25, 50, 75% or 100% sick leave/disability pension.
Marital status referred to whether the patient lived with another adult or not.
Education was divided into three categories referring to years of education since 1st grade: ≤9 years/9–12 years/> 12 years.
Medications. Use of analgesics/NSAID and psychotropics (meaning antidepressants and sedatives) was registered as positive when use was regular or as needed.
Self-administered questionnaires at baseline and follow-up
Pain distribution (0–18)
The localization and distribution of pain were reported in a self-administered pain drawing with 18 predefined body regions [18].
The Fibromyalgia Impact Questionnaire (FIQ) (0–100)
The FIQ comprises 10 subscales of disabilities and symptoms, ranging from 0 to 100 [19], and it is validated for a Swedish FM population [20]. A higher total score indicates lower overall health status. The FIQ total score is calculated by the mean of the ten subscales [19]. A total score < 39 is considered to represent mild impairment, ≥39 to > 59 moderate impairment and ≥ 59 severe impairment [21]. The FIQ subscales for Pain intensity (FIQ pain) and global fatigue (FIQ fatigue) were also applied in the present study. The patients estimated their pain intensity/how tired they had been during the previous week on a VAS, ranging from 0 to 100 mm [19].
The Hospital Anxiety and Depression Scale (HADS) (0–21)
The HADS contains 14 statements, rated from 0 to 3. The scores build two subscales for anxiety (HADS-A) and depression (HADS-D), each ranging from 0 to 21, and higher scores indicate a higher degree of distress [22]. .A cut-off score of eight is suggested to indicate possible anxiety or depression [23].
Stress and Crisis Inventory (SCI-93) (0–140)
The SCI-93 comprises 35 clinical manifestations of stress. The participants rated to what extent they are interfered by the different symptoms in their daily life on a scale ranging from 0 “not at all” to 4 “very much”. The items include physical and mental sensations. The total score ranges from 0 to 140 and a higher score indicates more stress [24].
Short-form 36 (SF-36) (0–100)
The SF-36 is a generic instrument assessing health related quality of life, comprising eight subscales. The subscales build two composite scores, the Physical Component Summary (PCS) and the Mental Component Summary (MCS), ranging from 0 to 100. A higher score indicates better health related quality of life [25].
Leisure Time Physical Activity Instrument (LTPAI) (h)
The LTPAI assesses the amount of physical activity during a typical week. The LTPAI total score is the sum of hours for the activities [26].
Tests of physical function at baseline
Six-minute walk test (6MWT) (m)
The patient was instructed to walk as quickly as she could without running and the baseline values of the distance in metres covered in 6 min was used as a measure of walking capacity in the analyses of predictors of improvement in pain intensity in the present study. The test has shown satisfactory test-retest reliability in a Swedish FM population [27]. The 6MWT was used only in the analyses of predictors of improvement of pain intensity in the present study.
Statistics
Descriptive statistics are presented as mean, standard deviation (SD) and range (min-max) for continuous variables and as number and percent for categorical variables.
For comparisons over time within the cohort, Wilcoxon’s Signed rank test was used for change over time in continuous variables and Sign test for dichotomous and ordinal categorical variables. Bootstrapped (10000 replicates) 95% confidence intervals were calculated for change over time in continuous variables.
Logistic regression analyses were used to analyze which variables were significant predictors of improvement in pain intensity [28]. Dependent variable was at least 50% improvement in pain intensity as reported on FIQ pain after 10 to 2 years (0 = < 50% improvement or no improvement/1 = ≥50% improvement). Independent variables were baseline values for age, education, BMI, FIQ total score, FIQ pain, HADS-A, HADS-D, SF-36 PCS, SF-36 MCS, LTPAI, 6MWT and group of randomization in previous RCT.
Odds ratios (OR) with 95% confidence intervals and p-values are presented.
The independent variables that were associated (p < 0.1) with the dependent variable in the univariable logistic regression analyses were included in the multivariable forward stepwise logistic regression analysis. All univariable regression analyses were adjusted for FIQ pain at baseline. Odds ratios (OR) with 95% confidence intervals, p-values and area under the receiving operating curve (AUC) values [29] are presented. AUC-values ranging from 0.7 to 0.8 indicate acceptable goodness of the model, values from 0.8 to 0.9 indicate excellent goodness and over 0.9 indicate outstanding goodness of the model [29]. For comparisons between patients followed-up and lost to follow-up, the Mann Whitney U-test was used for continuous variables, Fisher’s exact test for dichotomous variables and Mantel- Haenszel chi-square test for ordinal categorical variables.