Background
The research criteria of fibromyalgia (FM) as defined by the American College of Rheumatology (ACR) criteria for FM include a history of widespread pain for at least three months and pain on manual palpation in 11 of 18 tender points [
1]. FM is characterized by persistent widespread pain, increased pain sensitivity and tenderness [
1]. Other associated symptoms are fatigue, psychological distress [
1,
2], activity limitations [
3] and impaired physical capacity [
4]. The prevalence of FM ranges from 1 to 3% in the general population, it is more common among women and increases with age [
2,
5].
Activity limitations in FM have an impact on work ability [
6]. FM imposes a heavy patient burden in terms of disability, loss of quality of life and costs, and it imposes an economic burden on society [
7]. The degree of employment in FM varies geographically, with a range from 34% to 77% in different studies [
8]. The wide range is related to differences in the social benefit systems and labour markets of different countries [
8]. Working women with FM have previously been reported to experience less pain, less fatigue and better functional status than nonworking women with FM [
9]. Severe pain and fatigue combined with a demanding life situation and ageing have been associated with work disability in FM, as well as self rated disability and unmarried status [
10,
11].
Disability benefits in Sweden are approved when a disease impairs a person’s ability to work by at least 25%. Approximately 72% of all women in Sweden of working age (16–64 years) were employed in the year 2005 and 8% received full-time disability benefits1.
Interview studies have indicated that the severity of symptoms and psychosocial and environmental factors influence work disability in women with FM [
3,
8,
11‐
14]. These findings are supported by results of surveys conducted in large populations [
6,
10]. However, it is difficult to define to which extent symptom severity can be compatible with work. Assessments of physical, social and psychological health components combining subjective ratings with performance-based tests would advance our understanding in this area.
Objective
The purpose of this study was to investigate which aspects of health differ between working women (WW) with FM and nonworking women (NWW) with FM. We hypothesized that WW with FM would display better health than NWW with FM in terms of subjective ratings of health and performance-based tests of physical capacity.
Results
Study population
The mean age was 45.7 years (SD 8.7). The mean duration of symptoms was 10.5 years (SD 7.1). The mean number of tender points was 14.8 (SD 2.4) and the mean pain threshold was 171 kPa/sec (SD 66). There were no significant differences in pain threshold or the number of tender points between WW and NWW.
Type I error
The between-group analyses comprised a total of 33 statistical analyses, with 11 significant values at significance level 0.01, and the upper level of number of false significances was 0.2, which indicates that 0–1 of the significances found might be false.
Personal- and environmental factors
Personal factors
No significant differences were found between WW and NWW in personal factors.
Environmental factors
No significant differences were found between WW and NWW in environmental factors (see Table
1).
Table 1
Personal- and environmental factors in working women (WW) and nonworking women (NWW) with fibromyalgia
Personal factors
|
Mean (SD)
|
Median (range)
|
Mean (SD)
|
Median (range)
| |
Age, years
| 45.4 (8.1) | 47 (22–57) | 46.0 (9.2) | 47 (24–60) | 0.567 |
Symptom duration, years
| 11.7 (5.8) | 10 (2–24) | 9.7 (7.9) | 8 (0.3-45) | 0.021 |
FIQ feel good, 0-100
| 69.0 (28.9) | 71 (0–100) | 81.3 (22.7) | 86 (0–100) | 0.014 |
|
N (%)
| |
N (%)
| | |
Living with an adult | 45 (84.9) | | 55 (72.4) | | 0.133 |
Born outside of Sweden | 8 (15.1) | | 13 (17.1) | | 0.813 |
Education: | | | | | |
≤ 9 years | 11 (20.8) | | 17 (22.7) | | |
10 – 12 years | 29 (54.7) | | 40 (53.3) | | |
>12 years | 13 (24.5) | | 18 (24.0) | | 0.843 |
Pharmacological treatment: | | | | | |
Analgesic/NSAID, yes
| 31 (58.5) | | 58 (76.3) | | 0.035 |
Psychotropics, yes
| 22(41.5) | | 37 (48.7) | | 0.475 |
Environmental factors
|
Mean (SD)
|
Median (range)
|
Mean (SD)
|
Median (range)
| |
MOS-SSS, 4-20
| 15.4 (4.0) | 16 (7–20) | 14.5 (4.1) | 15 (4–20) | 0.267 |
Mean income in area of residence, 1000 Swedish kronor
| 214 (30.1) | 214 (165–299) | 201 (29.7) | 205 (123–267) | 0.042 |
Body function
No significant differences were found between WW and NWW.
Self rated body function
The number of pain localizations was fewer in WW than in NWW (p = 0.009) and pain (FIQ pain) was milder in WW than in NWW (p < 0.001). Stiffness (FIQ stiffness) was milder in WW than in NWW (p = 0.009). Fatigue was less severe in WW than in NWW (FIQ fatigue p = 0.006, MFI physical fatigue p = 0.001, MFI reduced activity p = 0.001 and MFI mental fatigue p = 0.006). WW rated a lower level of depression (HADS-D) than NWW (p = 0.007). Fifty-two percent of NWW and 29% of WW scored above the cut-off score for possible depression. There was no significant difference in anxiety (HADS-A) between WW and NWW. Fifty-eight percent of the NWW and 47% of the WW scored above the cut-off score for possible anxiety (8).
Activity and participation
No significant differences were found between WW and NWW in leisure time physical activity (LTPAI) or activity limitations in daily life (FIQ physical function).
Health status
A better disease specific health status (FIQ total, eight-item) was found in WW than in NWW (
p = 0.001). This was also true for physical health related quality of life (SF-36 PCS) (
p < 0.001) (see Table
2).
Table 2
Body function, activity and health status in working women (WW) and nonworking women (NWW) with fibromyalgia
Body function,
|
Mean (SD)
|
Median (range)
|
Mean (SD)
|
Median (range)
| |
Performance-based tests
| | | | | |
6MWT, meters
| 520 (95.6) | 524 (136–674) | 500 (75.8) | 512 (295–686) | 0.087 |
Grippit right hand, Newton
| 160.3 (67.1) | 155 (27–323) | 146.1 (67.6) | 160 (13–334) | 0.284 |
Grippit left hand, Newton
| 158.6 (73.2) | 155(17–349) | 144.3 (65.4) | 147 (19–319) | 0.343 |
Body function, ratings
| | | | | |
Pain localizations, number
| 12.5 (3.3) | 13 (5–18) | 14.0 (3.2) | 14 (5–18) |
0.009
|
FIQ pain, 0-100
| 62.5 (17.1) | 63 (26–100) | 77.0 (17.0) | 80 (26–100) |
<0.001
|
FIQ fatigue, 0-100
| 75.4 (22.4) | 83 (15–100) | 84.8 (17.1) | 90 (19–100) |
0.006
|
FIQ morning tired, 0-100
| 76.9 (20.7) | 81 (10–100) | 83.6 (18.9) | 89 (2–100) | 0.017 |
FIQ stiffness, 0-100
| 64.0 (27.6) | 75 (15–97) | 75.6 (23.7) | 82 (10–100) |
0.009
|
FIQ anxiety, 0-100
| 42.1 (32.6) | 38 (0–96) | 52.5 (35.1) | 54 (0–100) | 0.060 |
FIQ depression, 0-100
| 39.2 (31.7) | 32 (0–96) | 48.5 (32.5) | 51 (0–100) | 0.116 |
HADS-A, 0-21
| 7.5 (4.8) | 7 (1–19) | 9.7 (5.2) | 9 (1–20) | 0.021 |
HADS-D, 0-21
| 6.2 (2.9) | 6 (2–15) | 8.0 (3.9) | 8 (1–16) |
0.007
|
MFI General Fatigue, 4-20
| 16.8 (3.0) | 18 (9–20) | 18.0 (2.4) | 19 (12–20) | 0.021 |
MFI Physical Fatigue, 4-20
| 16.2 (3.2) | 17 (9–20) | 18.0 (2.2) | 19 (10–20) |
0.001
|
MFI Reduced Activity, 4-20
| 14.5 (3.3) | 14 (8–20) | 16.5 (3.5) | 17 (7–20) |
0.001
|
MFI Reduced Motivation, 4-20
| 9.7 (3.1) | 10 (5–16) | 10.9 (4.3) | 11 (4–19) | 0.123 |
MFI Mental Fatigue, 4-20
| 13.5 (3.5) | 14 (5–20) | 15.1 (4.0) | 16 (4–20) |
0.006
|
Activity and participation
| | | | | |
LTPAI, hours
| 4.5 (3.9) | 3 (1–23) | 5.4 (3.7) | 4 (1–18) | 0.088 |
FIQ physical function, 0-100
| 39.8 (20.5) | 40 (3–90) | 49.9 (23.1) | 53 (0–100) | 0.013 |
Health Status
| | | | | |
FIQ total, 8-item, 0-100
| 58.7 (17.1) | 63.5 (16–88) | 69.3 (14.5) | 71.3 (25–95) |
0.001
|
SF-36 PCS, 0-100
| 32.6 (8.0) | 33.3 (15–48) | 27.0 (7.0) | 27.6 (11–46) |
<0.001
|
SF-36 MCS, 0-100
| 41.6 (12.7) | 43 (17–68) | 36.8 (13.4) | 37.5 (16–64) | 0.043 |
Stepwise multiple logistic regression analyses
Variables displaying a significant difference (p ≤ 0.010) between WW with FM (n = 53) and NWW with FM (n = 76) were included in stepwise multiple logistic regression analysis. FIQ pain (n = 128) was the only statistically significant variable to independently explain work (OR 0.95, CI 0.93- 0.98), p < 0.001, (AUC 0.75, CI 0.66- 0.83).
Discussion
The main finding in this study was that working women (WW) with FM displayed better ratings than nonworking women (NWW) with FM in terms of pain, fatigue, stiffness, depression, disease specific health status and physical health related quality of life, which represent body functions and overall health status.
Physical capacity did not differ significantly between WW and NWW in terms of performance-based tests (see Table
2) where both groups presented lower capacity than the average population [
20,
21]. This supports earlier studies showing impaired body function in women with FM [
4,
29]. However, the physical work demands might influence the work ability in persons who have an impaired physical capacity. Earlier studies have reported the importance of the work environment in women with FM [
8,
11,
13,
30‐
32] and in other rheumatic diseases [
33].
The number of pain localizations was significantly lower in WW than in NWW and global pain (FIQ pain) was significantly milder in WW than in NWW (see Table
2). The mean pain (FIQ pain) of WW was well above 50 (0–100), which corresponds to the average pain level in previous studies of FM [
34]. Mean pain was above 75 (0–100) in NWW, which corresponds to the ratings of severely afflicted patients with FM [
34]. FIQ pain was found to be the only independent explanatory factor for work in this study. Pain has previously been found to be a critical factor for work in rheumatic diseases [
10,
35]. Our results indicate that women with FM having moderate pain generally could be expected to work. Some women appear to be able to work despite severe pain, which raises the question if there are workplace related factors that support their ability to work [
32,
36]. The influence of work related factors on work ability in FM need to be further studied.
Global fatigue (FIQ fatigue) was found to be significantly lower in WW than in NWW as well as physical fatigue (MFI-20), reduced activity (MFI-20), and mental fatigue (MFI-20) (see Table
2). Fatigue has previously been found to be an important factor for work disability in rheumatic diseases [
35]. However, our results showed severe global fatigue (FIQ fatigue) with mean ratings of over 70 (0–100) [
34] also in WW, indicating that fatigue might not be a critical factor for work disability.
Depression was rated significantly lower in WW than in NWW in the HADS, assessing depression. This supports the results of an earlier study on work disability in FM reporting the negative impact of depression symptoms on work ability [
37].
WW displayed a significantly better disease specific health status (FIQ total, eight-item) than NWW (see Table
2). This supports the results from an earlier study on work disability in FM where the FIQ total score was found to predict work disability [
6]. Physical health-related quality of life (SF-36 PCS) was significantly higher in WW than in NWW (see Table
2), which is in line with a previous study of FM [
38]. However, the quality of life of workers in our population, assessed by SF-36, was very low as compared to a national sample [
39]. Impaired health status assessed by SF-36 has earlier been associated with work disability in rheumatoid arthritis (RA) [
35], systemic lupus erythematosus (SLE) [
40] and musculoskeletal pain [
41].
The theory of the healthy worker effect suggests that healthier individuals are more likely to remain in the workforce [
42]. On one hand, this agrees well with the results of the present study. On the other hand, work is an important factor for health status in women in general [
43,
44] and in women with FM [
38]. Further studies are needed to explore if working women with FM maintain their health status, or if it deteriorates over time.
The main strength of the present study is the integration of physical, social and psychological assessments including subjective ratings as well as clinical assessments and performance-based tests of physical capacity. About 40% of the patients in this study worked part-time or full-time which is in line with international reports of work ability in FM [
8]. No significant differences were found in age, symptom duration, cohabitation, ethnicity, education, pharmacological treatment, mean income in the area of residence and social support, i.e. personal and environmental barriers or facilitators for health [
16]. A limitation of this study is the cross sectional design which does not allow analyses of cause and effect. Also, the specific demands in work were not reported in the study and need further investigation.
Conclusions
Working women with FM reported better health than nonworking women with FM in terms of pain, fatigue, stiffness, depression, disease specific health status and physical aspects of quality of life, which represent body functions and overall health status. However, they were equally impaired in tests of physical capacity. Moderate pain levels were compatible with work, while severe pain appeared to compromise work. Fatigue was better tolerated, as women scoring severe levels of fatigue worked.
Acknowledgements
We thank Anna Ericsson, Lena Nordeman, Maud Arndorw, Mona Lind, Mattias Hjelm and Ann-Kristine Neuman for examining the patients. The statistical advisers were Nils-Gunnar Pehrsson and Aldina Pivodic.
Funding
This work was supported by The Swedish Research Council, the ALF at Sahlgrenska University Hospital, the Research and Development Council of Göteborg and Södra Bohuslän, Västra Götaland Region, Sweden
No financial or non-financial interests exist, which could create a potential conflict of interest with regard to the work.
Competing interests
The authors declare that they have no competing interests.
Authors’ contributions
AP participated in the design of the study, performed the statistical analysis and drafted the manuscript. JB participated in the design of the study and helped to draft the manuscript. KM conceived of the study, and participated in its design and helped to draft the manuscript. All authors read and approved the final manuscript.