Abstract
Background and aims
This study has two main aims: (1) To explore the overlap between classification criteria in patients with Chronic Widespread Pain (CWP) and (2) To explore the use of the Patient Generated Index (PGI) as a quality of life (QoL) measure in this patient group.
Methods
Patients with Widespread Pain (ICD-11: pain in four or more out of five bodily regions, i.e. the four quadrants and axially) in a tertiary pain outpatient clinic were assessed according to classification criteria for Fibromyalgia [FM, American College of Rheumatology (ACR) criteria of 1990, 2010, 2011 and 2016], Chronic Fatigue Syndrome [CFS, Fukuda, Canada and International Consensus Criteria (ICC)] and Bodily Distress Syndrome (BDS). Furthermore, patients completed the PGI to assess QoL, and electronic questionnaires including demographic variables and standardised patient-reported outcome measures (PROMs).
Results
All patients (n=33) fulfilled the criteria for musculoskeletal type single-organ BDS, 81.8% met the 2016 modified criteria for FM, 30.3% met the Canada criteria for CFS and 24.2% met the criteria for multi-organ type BDS. There was substantial agreement between the 2016 and the 2011 and 2010 criteria sets for FM compared to the 1990 criteria (κ=0.766 and 0.673 compared to 0.279). Patients generally scored low on the PGI, indicating poor QoL (mean PGI 28.9, SD 19.8, range 0–100).
Conclusions
Our findings support the use of the term musculoskeletal type single-organ BDS to describe patients with CWP and the 2016 revision of the FM criteria. The PGI provides useful clinical information which is not captured by standardised PROMs.
Implications
The terminology of CWP has become less ambiguous as the new ICD-11 is closely related to the generalised pain criterion of the modified 2016 FM definition. Studies based on the 1990 classification criteria for FM should not be directly compared to studies based on later criteria set. The PGI may be a supplement to other measurements to portray patients’ individual concerns in patients with complex symptom disorders.
1 Introduction
According to the Global Burden of Disease report of 2015, Norway reports the highest number of years lost to premature mortality or disability due to musculoskeletal complaints (MSCs) in the world [1]. These disorders generated the highest health care costs in Norway of all diagnostic groups in 2011, accounting for more than one-third of all health-related welfare grants [2]. Annually, approximately one-third of the Norwegian population consults with a primary health care provider with MSCs [3].
Chronic pain has been defined as pain persisting 3 months or more, beyond which tissue healing should be expected [4]. Across 24 countries, prevalence rates vary from 11 to 55%, with an estimated mean of 31% in males and 40% in women [5], [6], [7]. Chronic pain involving multiple bodily regions, Chronic Widespread Pain (CWP), is a characteristic feature of conditions such as Fibromyalgia (FM), Chronic Fatigue Syndrome (CFS) and other so-called functional somatic syndromes. This phenomenon has been defined in various ways, making research findings hard to compare [8].
In 1990, the American College of Rheumatology (ACR) defined CWP as pain located bilaterally, above and below the waist as well as axially, persisting for 3 months or more [9]. Prevalence rates using this definition are estimated between 10 and 15% [7], [10], [11]. This definition constitutes the mandatory CWP criterion of the 1990 criteria for FM in addition to a tender point count upon clinical examination [9]. With the revisions made to the classification criteria in 2010 and the 2011 modification, this criterion as well as the tender point count were suggested abandoned in favour of self-reports of pain and non-pain symptoms including fatigue [12]. These revisions have been criticised to allow for patients with regional pain conditions such as e.g. upper back, neck and one arm to be diagnosed with FM. In order to avoid such misclassification, the ACR launched the term “generalised pain criterion” as part of the 2016 modified criteria for FM: pain in four out of five bodily regions, relating to the four extremities and the axial region [13]. This term is closely related to the recent definition of CWP by the ICD-11: diffuse pain in four out five body regions (three quadrants and axially), associated with significant emotional distress or functional disability [14].
In addition to profound fatigue, CWP is also a characteristic feature of CFS, as defined by the Fukuda, Canada and International Consensus Criteria (ICC) [15], [16], [17]. One study found that 58% of FM cases in the general population met the criteria for CFS [18]. A co-occurrence of these syndromes might be expected due to the case definitions, where fatigue is one of the main supporting symptoms in the FM 2010, and the modified 2011 and 2016 criteria and musculoskeletal pain is common in patients with CFS. There is great controversy regarding whether the two conditions may be part of a common underlying construct [19], [20].
Another recently defined syndrome which may be characterised by CWP is Bodily Distress Syndrome (BDS) [21], [22], [23]. In one study including patients in primary and secondary care, BDS captured all cases of FM and CFS, in addition to at least 90% of patients with eight other functional somatic syndromes [24].
How do we assess what is meaningful and important to the patients suffering from chronic conditions? It has been recommended that in addition to the clinical perspective, the patient perspectives should be addressed through so-called patient-reported outcome measures (PROMs) [25]. PROM has been defined as “any report of the status of the patient’s health condition that comes directly from the patient, without interpretation of the patient’s response by a clinician or anyone else” [26]. The Person Generated Index (PGI) is a QoL measure based on the patients’ individual selection and weighting of areas which are important in their lives [27], [28]. The PGI may be especially useful in assessing QoL in patients with complex symptoms as instruments assessing pain or functional ability may not portray the patients’ individual concerns.
In the tertiary outpatient pain clinic at Oslo University Hospital, a large number of patients present with CWP. As part of a randomised controlled pilot study, we assess the degree of overlap between classification criteria of FM (ACR 1990, 2010, and the 2011 and 2016 modifications), CFS (Fukuda, Canada and ICC criteria), and BDS in patients with CWP to test the hypothesis that one over-riding concept may capture all classification criteria. Secondly, we explore the use of the Patient Generated Index (PGI) as a QoL measure in this patient group.
2 Methods
2.1 Setting and participants
The Department of Pain Management and Research at Oslo University Hospital is an outpatient pain clinic treating around one thousand new patients annually suffering from chronic pain of all aetiologies. Many of the patients receive interdisciplinary care based on a biopsychosocial framework, by at least two health care providers (physician and physiotherapist, and/or psychologist, and/or occupational therapist and/or nurse).
2.2 Recruitment
Patients were recruited through referrals from primary or secondary care, which were identified by an established interdisciplinary team. Patients found potentially eligible for the study were contacted by the research team and consulted with a research physician (HTM). Patients who fulfilled the inclusion criteria were invited to participate in the study and signed a consent form. Patients who declined to participate and non-eligible patients received usual care. To ensure adequate recruitment, a brief description of the study and inclusion criteria were published on two closed electronic discussion forums for GPs. The recruitment period was from September 2016 to March 2017.
2.3 Inclusion criteria
Inclusion criteria were (1) age 18 or more; (2) pain in at least four out of five bodily regions (defined as the four quadrants and axially); (3) pain persisting 3 months or more; (4) the patient was able to give informed consent and benefit from group therapy (including sufficient cognitive capacity and language skills); (5) no other medical condition could better explain the symptoms. There were no other exclusion criteria.
2.4 Design
The study is based on baseline data from an ongoing randomised controlled study at the clinic, where patients were randomised either to treatment as usual or a group-based multidisciplinary pain intervention (the MUD-PI).
2.5 Variables
2.5.1 Patient characteristics
We describe the patient population according to sex, age, educational level, and work status including receipt of health care grants. In addition, we assessed the number of years patient had lived with pain, and the number of pain regions reported on an electronic manikin.
2.5.2 Diagnostic variables
2.5.2.1 Fibromyalgia (FM)
During the initial consultation, one of the authors (HTM) assessed FM using the ACR 1990 and 2010 criteria, and the modified criteria of 2011 and 2016. A full clinical history and clinical examination including a tender point count was performed. To fulfil the 1990 criteria, a positive CWP criterion (pain bilaterally, above and below the waist and axially) and a tender point count of 11 or more out of 18 upon physical examination were required [9]. For the 2010 criteria and the 2011 modifications, a Widespread Pain Index (WPI) and a symptom severity score (SSS) were recorded. For the WPI, patients filled in a body manikin indicating the number of painful bodily regions experienced during the previous 7 days (range 0–19): Neck, upper back, lower back, abdomen, and the following left/right: jaw, shoulder, upper arm, lower arm, hip/buttocks, upper leg and lower leg. The SSS is based on self-reports of fatigue, unrefreshed sleep and cognitive impairment (memory and concentration) (scores 0=“no problem” to 3=“severe problem”). Both the 2010 and 2011 criteria require a WPI score≥7 and SSS≥5 or WPI from 3 to 6 and SSS≥9. In addition, the 2010 criteria require a physician’s assessment of the number of symptoms the patient presents (0=“no symptoms” to 3=“many symptoms”), whereas in the 2011 modified criteria, the same three points may be scored based on self-reports of irritable bowel symptoms, depression and headache [12], [29]. The 2016 modified criteria require the generalised pain index, i.e. pain in four out of five bodily regions relating to the four quadrants and the axial region (exempt head, abdomen and chest), in addition to WPI≥7 and SSS count≥5 or WPI from 4 to 6 and SSS≥9 [13].
2.5.2.2 Chronic fatigue syndrome (CFS)
Through a thorough symptom history, the criteria for CFS (Fukuda, Canada and ICC criteria sets) were assessed [14], [15], [16]. The Norwegian directorate of health recommends the Canada criteria [30]. The department does not routinely perform blood tests or imaging.
2.5.2.3 Bodily distress syndrome (BDS)
The 25-item BDS checklist is part of the standard electronic set of questionnaires at the clinic. It addresses symptoms within four categories (cardiopulmonary, gastrointestinal, musculoskeletal and general symptoms group) [20]. For single organ-type BDS, patients must have moderate or severe symptoms from 1 to 3 symptom groups, whereas the multi-organ type requires symptoms from all four groups.
2.5.3 The Patient Generated Index (PGI)
The PGI was developed as an individualised quality of life (QoL) measure [31]. QoL has been described as “the extent to which our hopes and ambitions are matched by experience”, where the aim of health care providers would be to “narrow the gap” between expectations and present reality [32]. The PGI has been validated for various clinical conditions [33], [34] and the Norwegian version is validated for low back pain (LBP) and rheumatic conditions [27], [28].
The PGI is completed in three steps. First, patients are to indicate up to five areas of life which are important to them, and which have been affected by their health condition. Secondly, they rate the present situation in each area on a scale from zero to six (0=“as bad as can be”, 6=“as good as can be”). Finally, the patient spends 10 points among the listed areas to weight their importance. An index score is calculated (range 0–100), where a higher score indicates a higher QoL. To minimise measurement errors, it has been estimated that a statistical clinical change should be set at approximately 30 points at an individual level and 5 points on group level [28].
2.5.4 Standardised health measures
All standardised questionnaires are part of the clinic’s established electronic questionnaire set completed 1 h before the first clinical consultation at the outpatient clinic. The patients are asked to answer the following questionnaires in the order presented.
2.5.4.1 The Pain Catastrophizing Scale (PCS)
The Pain Catastrophizing Scale (PCS) [35] assesses catastrophizing thoughts related to pain by means of 13 items on a five-point scale (0=“not at all” to 4=“all the time”). A sum score (0–52) is calculated, the max score indicating the highest level of catastrophizing. The PCS has been validated for Norwegian LBP patients [36].
2.5.4.2 The Insomnia Severity Index (ISI)
The Insomnia Severity Index (ISI) is a seven-item questionnaire which addresses the nature, severity and impact on life of sleep patterns during the last month on a five-point Likert scale (0=“no impact” to 4=“severe impact”), with a sum score from 0 to 28 [37]. Individuals with scores of 11 or more may potentially benefit from treatment. The ISI is considered a reliable and valid measure [37], [38].
2.5.4.3 The Chalder Fatigue Questionnaire (CFQ)
The Chalder Fatigue Questionnaire assesses fatigue by means of seven items related to physical symptoms and four items related to mental symptoms (0=“better than usual” to 3=“much worse than usual”), yielding a sum score of 0–11 [39]. The instrument has good reliability and validity [39], [40] also for a Norwegian population [41].
2.5.4.4 The General Self-efficacy Scale (GSE)
The General Self-efficacy Scale (GSE) is used to assess the patient’s perceived self-efficacy [42], independent of any co-existing medical condition or disability. Perceived self-efficacy has been defined as “the belief that one can perform a novel or difficult task or cope with adversity”, and can be regarded as a resource factor. The scale consists of 10 items scored on a four-point scale, (1=“not at all true” to 4=“exactly true”), giving a sum score [10], [11], [12], [13], [14], [15], [16], [17], [18], [19], [20], [21], [22], [23], [24], [25], [26], [27], [28], [29], [30], [31], [32], [33], [34], [35], [36], [37], [38], [39], [40]. We used the validated Norwegian version [43].
2.5.4.5 The Hopkin’s Symptom Checklist (HSCL-25)
The Hopkin’s Symptom Checklist (HSCL-25) assesses psychological distress by means of 25 items covering symptoms of anxiety, depression and somatisation during the past week, and includes a question addressing suicidal thoughts [44]. Each item is scored on four point scales (0=“not at all”, 4=“to a large extent”), where a score above 1.5 for men and 1.75 for women indicates psychological distress. The Norwegian version has been validated [45].
2.5.4.6 The Euro-qol instrument (EQ-5D)
The Euro-qol instrument [46] is a commonly used generic QoL measure. The EQ-5D has been validated for a vast number of conditions whereas the Norwegian version has been validated for LBP patients only [47]. The EQ-5D-5L consists of five health dimensions: mobility, self-care, usual activities, pain/discomfort and anxiety/depression, in addition to a Visual Analogue Scale (VAS) (0–100) to assess general health. Each dimension has five levels of severity (1=“no problem” to 5=“extreme problems”) [48]. An index score for QoL is often presented, (−0.59=“less than dead” to 1=“best possible”).
2.5.4.7 The Numeric Rating Scale (NRS)
The Numeric Rating Scale (NRS) is a 11-point scale used to assess pain intensity, ranging from 0 to 10, 10 being the highest possible level of pain [49]. In this study we present results of a mean NRS during the past week.
2.5.4.8 The Oswestry disability index (ODI)
The Oswestry disability index (ODI) was developed as a measure of functional ability in patients with LBP, for which the Norwegian version is validated [45]. It has also been validated in a number of other clinical settings [50], [51]. It consists of 10 dimensions: pain intensity, personal care, lifting, walking, sitting, standing, sleeping, sex life, social life and travelling. Each dimension is scored from 1 to 6 (1=“best possible function” to 6=“worst possible function”). A sum score is calculated as the mean of the 10 categories and expressed as a percentage, a higher score indicating a higher level of disability.
2.6 Statistical analyses
Patients for whom we did not have complete data for the analyses were excluded from this study. Descriptive statistical methods, including frequencies, percentages, mean and median values, and standard deviation (SD) were used to describe patient characteristics and variable scores. Paired samples t-tests and ANOVA were used to calculate between-group differences. Pearson’s correlation coefficients were calculated to assess correlation between variables, interpreted according to Cohen; r=0.1–0.29=small, 0.3–0.49=moderate and 0.5–1.0=strong correlation [52]. Agreement between diagnostic criteria and health measures was assessed using kappa statistics. Cohen’s kappa coefficient was interpreted according to Landis and Koch: <0=“less than chance”, 0.001–0.2=“slight agreement”, 0.21–0.4=“fair agreement”, 0.41–0.6=“moderate agreement”, 0.61–0.8=“substantial agreement”, 0.81–0.99=“almost perfect agreement” [53]. Significance level was set at 0.01.
The SPSS for Windows version 24 was used throughout the study [54].
3 Results
Forty-nine patients were found to be potentially eligible for the study. Four patients did not have the necessary language skills and one patient was not considered to have the cognitive skills to benefit from group therapy. Four patients declined to participate and three patients did not meet the inclusion criteria after the initial consultation. All patients completed the electronic questionnaires and were assessed according to the diagnostic criteria (n=37). Four cases were excluded due to incomplete PCS, GSE, ISI, or BDS questionnaires (n=33, response rate of 89.1%).
Patient characteristics and corresponding PGI scores are displayed in Table 1. Patients had experienced pain for an average of 12.5 years (median 9, SD 10.0, range 1.5–37 years). Upon physical examination, 81.9% of patients fulfilled the tender point criterion (≥11/18 tender points), with a mean of 14.7 positive tender points (median 16, range 3–18). Mean WPI scores were 12.1 (median 12, SD 3.33, range 7–19), and mean SSS for the 2010 criteria was 7.8 (median 8, SD 2.63, range 3–12), whereas the mean SSS for 2011 and 2016 was 7.72 (median 8, SD 2.70, range 2–12). Five patients scored less than five points on the SSS-scales. All patients fulfilled the WPI criteria for FM.
Percentage (n=33) | Mean PGI | Median PGI | SD | Range | |
---|---|---|---|---|---|
Sex | |||||
Women | 78.8 | 25.4a | 25.0 | 20.3 | 0–83.3 |
Men | 21.2 | 42.0 | 37.5 | 10.9 | 33.3–65.0 |
Age | |||||
25–34 | 18.2 | 23.3 | 20.0 | 7.03 | 16.7–33.3 |
35–44 | 27.3 | 22.6 | 30.0 | 14.4 | 0–36.7 |
45–49 | 12.1 | 21.3 | 19.2 | 24.8 | 0–46.7 |
50–54 | 24.2 | 31.9 | 25.8 | 29.4 | 0–83.3 |
55–70 | 18.2 | 45.1 | 44.2 | 8.27 | 36.7–58.3 |
Lives alone | |||||
Yes | 30.3 | 28.3 | 33.3 | 15.8 | 0–46.7 |
No | 69.7 | 29.2 | 25.0 | 20.4 | 0–83.3 |
Children <18 | |||||
Yes | 78.8 | 31.3 | 31.7 | 20.4 | 0–83.3 |
No | 21.2 | 20.1 | 20.0 | 15.7 | 0–37.5 |
Education (years) | |||||
1–10 | 15.2 | 37.0 | 33.3 | 17.7 | 20.0–65.0 |
11–13 | 45.5 | 24.3 | 25.0 | 21.1 | 0–58.3 |
14–17 | 33.3 | 26.1 | 30.0 | 11.8 | 0–37.5 |
17+ | 6.1 | 58.3 | 58.3 | 35.4 | 33.3–83.3 |
Work/studies/military | |||||
Yes | 39.4 | 36.0 | 33.3 | 16.9 | 0–65.0 |
No | 60.6 | 24.3 | 22.5 | 20.6 | 0–83.3 |
Out of work >2 years | |||||
Yes | 42.4 | 23.0 | 20.0 | 22.2 | 0–83.3 |
No | 54.5 | 33.6 | 35.0 | 17.7 | 0–65.0 |
Grants | |||||
None | 15.2 | 27.3 | 33.3 | 18.6 | 0–50.0 |
Sick-leave part-time | 9.1 | 33.9 | 33.3 | 7.52 | 26.7–41.7 |
Sick-leave full-time | 9.1 | 33.3 | 36.7 | 15.3 | 16.7–46.7 |
Work assessment allowance (AAP) | 42.4 | 26.3 | 25.0 | 26.2 | 0–83.3 |
Disability pension partly | 6.1 | 27.5 | 27.5 | 15.3 | 16.7–38.3 |
Disability pension full | 9.1 | 33.3 | 33.3 | 3.33 | 30.0–36.7 |
Other | 9.1 | 31.1 | 18.3 | 23.6 | 16.7–58.3 |
-
a p-Value<0.01.
-
PGI=Patient Generated Index; SD=standard deviation.
The percentage of patients fulfilling the different FM classification criteria, CFS criteria and single- and multi-organ BDS is presented in Table 2. All patients fulfilled the single organ-type BDS criteria, 97.0% fulfilled at least one FM criteria set, 39.4% met at least one CFS criteria set and 24.2% fulfilled multi-organ type BDS. Hence, the BDS multi-criteria were the strictest of the criteria accounted for in this study a small percentage fulfilled both a FM, a CFS and multi-organ type BDS (15.2%). Of patients who fulfilled at least one CFS criteria set, all fulfilled at least one FM criteria set. Looking specifically at the FM 2016 modified classification criteria for FM, 33.3% of the patients who met these criteria, 33.3% also meet the Canada criteria for CFS and 22.2% met the ICC criteria for CFS. Of the eight patients who met the BDS multi-organ type criteria, only one patient did not meet the ACR 2016 modified criteria for FM. Table 2 also presents the PGI scores for the different groups. There were no statistically significant difference in PGI scores between those who did and did not fulfil the different classification sets.
PGI |
Range |
|||||
---|---|---|---|---|---|---|
Percentage | Mean | Median | SD | |||
FM ACR 1990 | Yes | 75.8 | 26.6 | 25.0 | 20.0 | 0–83.3 |
No | 24.2 | 36.0 | 35.0 | 18.8 | 0–65.0 | |
FM ACR 2010 | Yes | 84.8 | 29.2 | 31.7 | 20.3 | 0–83.3 |
No | 15.2 | 27.3 | 28.3 | 18.6 | 0–46.7 | |
FM ACR 2011 | Yes | 87.9 | 29.6 | 33.3 | 20.1 | 0–83.3 |
No | 12.1 | 23.8 | 24.2 | 19.4 | 0–46.7 | |
FM ACR 2016 | Yes | 81.8 | 30.5 | 33.3 | 20.0 | 0–83.3 |
No | 18.2 | 21.9 | 24.2 | 19.2 | 0–46.7 | |
CFS Fukuda | Yes | 30.3 | 28.3 | 22.5 | 28.2 | 0–83.3 |
No | 69.7 | 29.2 | 33.3 | 15.7 | 0–58.3 | |
CFS Canada | Yes | 30.3 | 25.6 | 30.8 | 21.5 | 0–65.0 |
No | 69.7 | 30.4 | 30.0 | 19.4 | 0–83.3 | |
CFS ICC | Yes | 21.2 | 20.5 | 16.7 | 24.3 | 0–65.0 |
No | 78.8 | 31.2 | 33.3 | 18.3 | 0–83.3 | |
BDS single-organ type | Yes | 100 | 28.9 | 30.0 | 19.8 | 0–83.3 |
BDS, multi-organ type | Yes | 24.2 | 41.5 | 37.5 | 24.9 | 0–83.3 |
No | 75.8 | 24.9 | 24.5 | 16.6 | 0–58.3 |
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ACR=American College of Rheumatology; FM ACR 1990=ACR criteria for FM of 1990; FM ACR 2010=ACR criteria for FM of 2010; FM ACR 2011=ACR criteria for FM of 2011; FM ACR 2016=ACR criteria for FM of 2016; Fukuda=Fukuda criteria for CFS/ME; Canada=Canada criteria for CFS/ME; ICC=International Consensus Criteria for CFS/ME.
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Mean=median; SD and range for Patient Generated Index Scores are presented.
Patients nominated in total 28 unique domains as important areas of life in their PGIs (Table 3).
Nominated domain | n | % | Total points | Mean points among domain nominators |
---|---|---|---|---|
Social life | 27 | 81.8 | 33.0 | 1.22 |
Job/career | 26 | 78.8 | 62.5 | 2.40 |
Physical activity | 19 | 57.6 | 28.5 | 1.47 |
Identity/self-image | 12 | 36.4 | 41.0 | 3.42 |
Being a parent/activity with children | 11 | 33.3 | 40.0 | 3.63 |
Hobbies/creativity | 8 | 24.2 | 13.0 | 1.63 |
Economy | 6 | 18.2 | 4.00 | 0.67 |
Sleep | 5 | 15.2 | 21.0 | 4.20 |
Partner | 5 | 15.2 | 10.0 | 2.00 |
Daily activities | 4 | 12.1 | 12.0 | 3.00 |
Fatigue | 4 | 12.1 | 5.00 | 1.25 |
Housework | 3 | 9.09 | 6.00 | 2.00 |
Mood | 3 | 9.09 | 9.50 | 3.17 |
Education | 3 | 9.09 | 5.00 | 1.67 |
Finding joy in activities | 3 | 9.09 | 4.00 | 1.33 |
Sex-life | 2 | 6.06 | 3.00 | 1.50 |
Being independent | 2 | 6.06 | 4.00 | 2.00 |
Cognitive function | 2 | 6.06 | 0 | 0 |
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Total points given in step 3 of the PGI are presented, where 10 points are divided across five nominated domains to weight the importance of each domain. Mean points represent the mean number of points (possible range 0–10) given to the domain by nominators of this domain. Domains nominated by at least two patients are presented.
Agreement between the different FM criteria is presented in Table 4. There is a strong agreement between the 2016 modified criteria and the 2010 and 2011 classification criteria sets. The mean and median scores on the standardised health questionnaires are presented in Table 5. The PGI had a moderate correlation to the GSE scale (r=0.441, p<0.05), but did not correlate with the other standardised questionnaires (Table 6). The strongest correlations were found between the PCS and HSCL-25 (r=0.773), the EQ-5D-5L and NRS (r=−0.702), the EQ-5D-5L and ODI (r=−0.694) and between the NRS and ODI (r=0.688) (p<0.01).
1990 | 2010 | 2011 | 2016 | ||
---|---|---|---|---|---|
1990 | κ | – | |||
2010 | κ | −0.04 | – | ||
2011 | κ | 0.006 | 0.872 a | – | |
2016 | κ | 0.279 | 0.673 a | 0.766 a | – |
-
a p-Value<0.01.
-
Cohen’s kappa (κ) for assessment of agreement is presented.
Mean | Median | SD | Range | |
---|---|---|---|---|
EQ-5D-5L | 0.43 | 0.40 | 0.23 | −0.2 to 0.70 |
ODI | 43.2 | 44.0 | 13.4 | 18.0–72.0 |
NRS | 6.21 | 6.00 | 1.36 | 4.00–9.00 |
PCS | 24.7 | 24.5 | 11.5 | 3.00–49.0 |
GSE | 3.09 | 2.80 | 2.22 | 1.60–15.0 |
HSCL-25 | 2.40 | 2.40 | 0.49 | 1.20–3.20 |
CFQ | 8.66 | 9.00 | 2.16 | 3.00–11.0 |
ISI | 16.8 | 17.0 | 5.78 | 2.00–27.0 |
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EQ-5D-5L=the EuroQol; ODI=Oswestry disability index; NRS=Numeric Rating Scale; PCS==Pain Catastrophizing Scale; HSCL-25=the Hopkin’s Symptom Checklist-25; GSE=General Self-efficacy Scale; ISI==Insomnia Severity index; CFQ=Chalder Fatigue questionnaire.
PGI | ODI | EQ-5D-5L | PCS | GSE | ISI | CFQ | NRS | HSCL-25 | |
---|---|---|---|---|---|---|---|---|---|
|
|||||||||
r | r | r | r | r | r | r | r | r | |
PGI | – | ||||||||
ODI | 0.048 | – | |||||||
EQ-5D | −0.151 | −0.694b | – | ||||||
PCS | 0.196 | 0.351 a | −0.430a | – | |||||
GSE | 0.441 a | 0.322 | −0.388a | 0.265 | – | ||||
ISI | 0.051 | 0.189 | −0.239 | 0.271 | 0.012 | – | |||
CFQ | 0.104 | 0.229 | −0.223 | −0.039 | −0.052 | −0.033 | – | ||
NRS | 0.143 | 0.688 b | −0.702b | 0.464 b | 0.317 | 0.382 a | 0.271 | – | |
HSCL-25 | 0.021 | 0.308 | −0.299 | 0.773 b | 0.033 | 0.452 a | −0.069 | 0.334 | – |
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aStatistically significant at level p<0.05.
-
bStatistically significant at level <0.01.
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PGI=Patient Generated Index; ODI=Oswestry disability index; EQ-5D-5L=the EuroQol; PCS=Pain Catastrophizing Scale; GSE=General Self-efficacy Scale; ISI=Insomnia Severity index; CFQ=Chalder Fatigue questionnaire; NRS==Numeric Rating Scale; HSCL-25=the Hopkin’s Symptom Checklist.
4 Discussion
4.1 Comparison with the literature
In this study of patients with CWP in a tertiary outpatient pain clinic, we found a marked degree of overlap between classification criteria sets for FM ACR 1990 and 2010 criteria, and the 2011 and 2016 modifications), CFS [Fukuda, Canada, (ICC)] and BDS. All cases were captured by the musculoskeletal type single-organ BDS. This supports the findings in a Danish study, where BDS captured all patients with FM (based on SCAN interview) and CFS (based on the Fukuda criteria) [24]. The BDS multi-organ-criteria were the strictest of the criteria accounted for in this study. Overlap between these diagnostic entities is often addressed in research, authors often arguing for or against the existence of a common underlying factor [19], [55], [56], [57], [58], [59]. However, the degree of overlap found in our study could be expected, given the overlap between case definitions and the large overall symptom burden.
The ACR modified classification criteria for FM of 2016 showed substantial agreement with the 2010 and 2011 classification criteria for FM, whereas there was poor agreement found with the 1990 criteria. Our findings support a further exploration of the 2016 criteria, as it avoids the possibility inherent in the 2010 and 2011 criteria of classifying patients with regional pain symptoms as FM. In addition, the 2016 criteria acknowledge the non-pain symptom characteristics of patients with FM, which the 1990 criteria did not. Our findings indicate that studies using the 1990 criteria for FM cannot be directly compared with studies using later classification criteria for FM.
The PGI as an individualised QoL measure has received increasing support as a means to gain insight into the patient-perspective, in addition to having a high responsiveness to change [25], [34], [58]. We found a mean PGI of 28.3 (SD) out of 100. A recent study reported mean PGI scores in patients with stroke, Multiple Sclerosis, HIV and advanced cancer of approximately 35, 50, 53 and 40, respectively [25]. In patients with rectal cancer, mean pre- and post-surgical PGI scores of 48 and 61 have been reported, respectively [59]. In Norwegian studies, patients with non-specific LBP and rheumatic disease have reported a mean PGI score of approximately 40 [27], [28]. Our findings suggest that patients with CWP have a substantially reduced self-defined QoL compared to patients with other clinical conditions. This is supported by a Norwegian study which reports that patients with chronic non-malignant pain report as poor QoL as palliative cancer patients [60]. This may reflect the challenge of living with a condition which is controversial, unpredictable and less well-defined than most somatic conditions.
We found that a higher self-defined QoL, as defined by the PGI, correlated with a higher self-perceived efficacy on the GSE. To our knowledge, this is the only study that has used both PGI and GSE. In other words, patients’ perception of their QoL in this study was related to the degree to which they believed in their own ability to cope and attain goals [61], [62]. In patient registers from the pain clinic, patients generally score high on the GSE, and often above expected in the general population (unpublished results). A recent systematic review on the prognostic value of self-efficacy on chronic musculoskeletal pain found an association between a high level of self-efficacy and health outcomes such as physical functioning, physical activity participation, health status, work status and lower levels of pain intensity and disability [63]. However, the overall quality of evidence was poor, and findings should be interpreted with caution [63].
In our study, there was no statistically significant correlation between scores on the PGI and the standardised PROMs besides the GSE. Other studies have found a low correlation between scores on the PGI and standardised measures in cancer patients [25], [64]. This could indicate that the PGI reflects different aspects of health-related QoL than the more common standardised measures, and to a larger degree capturing the patient perspective. In fact, in patients with lung cancer, only around 60% of the patients’ concerns were captured by the standardised instruments. In the lung cancer study, concerns which were not captured were, among others, concerns for the future (e.g. uncertainty), relationships (e.g. being dependent on others and worries for the family) and emotional problems [65]. Patients in our sample most frequently weighted social life, job/career, identity and family as the most important domains in their lives. These domains are not fully captured by the standardised PROMs. Areas of life which are important to patients living with chronic conditions should be further explored and should be included in standardised measures intending to capture QoL.
Scores on the standardised measures were generally higher than the individualised PGI scores. This is in line with findings among patients with MS, stroke and advanced cancer [25], [64]. The QoL indicated by a PGI score is the result of the patients’ self-defined areas of life, and patients are likely to nominate areas of life which are negatively affected by their condition, resulting in a low score. Standardised questionnaires, however, are likely to include some areas of life which are not affected in all patients, which may result in a higher overall score than on the PGI [25]. The PGI may detect positive changes over time more easily by avoiding a ceiling effect.
4.2 Strengths and limitations
The main limitation of this study is the small sample size and the highly selected population. The study population consisted of patients referred to a specialised pain clinic, who reported poor function and poor QoL. This might affect the generalisability of the data. The high prevalence of the conditions studied may also overrate the degree of overlap in this study.
A single physician performed the interviews and clinical examinations, and, hence, inter-rater reliability cannot be accounted for in all diagnostic assessment. However, this procedure avoids varying diagnostics from patient to patient. Some assessment, such as the BDS classification, did not depend on the clinician as it derived though an electronic form. All patients were interviewed and examined in a strict order according to the different diagnostic criteria and not to e.g. survey criteria for FM. The thorough clinical history and examination also limited the risk of symptoms being due to other conditions.
On completing the PGI, all patients received guidance by the physician who performed the diagnostic assessments. Although this might cause concerns for bias, many studies show that patients fill in PGI incorrectly, and interviewer guidance has been recommended [25], [66]. This may indicate that the PGI may be less applicable in clinical (non-research) settings.
5 Conclusion
In this study among patients with CWP in a tertiary outpatient pain clinic, there was a clear overlap between classification criteria for FM, CFS and BDS, the multi-organ type BDS being the most strict criteria set. All patients were captured by the term musculoskeletal type single-organ BDS, which supports a further exploration of this term to describe patients with CWP. Our findings also support the 2016 modified FM criteria, which showed moderate to substantial agreement with the previous criteria sets.
Patients in our study had low scores on the PGI, an individualised QoL measure, indicating that patients with CWP perceive their QoL poor compared to other patients with medical conditions such as advanced cancer, non-specific LBP and rheumatic conditions. The PGI had a moderate correlation to perceived self-efficacy but not to other standardised measures.
6 Implications
The field of pain research is rendered less ambiguous by the new ICD-11 definition of CWP, which corresponds to the generalised pain criterion of the modified 2016 ACR criteria for FM. The study indicates that studies based on the 1990 criteria set for FM are difficult to compare to studies based on the later criteria sets. A further exploration of the term BDS to describe patients with complex symptom syndromes is called for. The PGI might add unique dimensions in assessing QoL in patients with complex symptoms as it captures the patients’ perspective and individual concerns, and as such be ideal for a quantifiable and individual goal-setting outcome in pain rehabilitation contexts.
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Authors’ statements
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Research funding: The study was funded by the Norwegian Directorate of Health.
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Conflict of interest: The authors declare that they have no competing interests.
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Informed consent: Patients signed an informed consent form prior to being included in the study.
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Ethical approval: The study was approved by the Norwegian Regional Ethics Committee (2016/1127-1). The study is registered in clinicaltrials.gov: NCT03413501.
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Author contributions
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LPG made substantial contribution to conception of the study. HTM and LPG made substantial contributions to design. All authors made substantial contributions to acquisition of data and revisions of the manuscript. HTM performed the analyses of the study and drafted the manuscript, with major contributions from all authors. All authors read and approved the final manuscript.
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