Chronic, unexplained widespread pain is the clinical hallmark of the fibromyalgia syndrome. Adverse psychosocial factors, aspects of health beliefs and behavior, and a history of reporting somatic symptoms have been shown to predict the new onset of chronic widespread pain in the general population (1). It has also been hypothesized that physical trauma may be an important risk factor for widespread pain (2). Such trauma may occur as a result of, for example, a road traffic accident or a work place accident. Previous studies have shown an association between major physical trauma and the onset of fibromyalgia (3, 4). For example, Al Allaf et al (3) found that prior traumatic events were reported more commonly in patients with fibromyalgia than in age- and sex-matched controls (39% and 24%, respectively).
In contrast, the role of low-level physical trauma, which may occur by repeated exposure, for example, through manual handling activities within the work place, is unknown. Only 1 study has examined any aspects of work-related risk factors and chronic widespread pain (5). That study found the prevalence of fibromyalgia to be increased in subjects who reported high levels of “physical work stress.” No associations were found for “mental work stress.” However, that study was cross-sectional, and other aspects of the work place environment were not considered.
Recently, we reported that the role of work-related risk factors in predicting chronic widespread pain in an unselected population sample was limited (6). However, that conclusion may have been influenced by the “healthy worker effect.” The majority of subjects had been in the same employment for at least 3 years and were therefore likely to have been well-established within the work force. As a consequence, we may have underestimated the true effect of work-related risk factors and the new onset of widespread pain, since some individuals may have previously left the work force as a result of their pain. The aim of the present study was to examine the effect of work-related risk factors as predictors of new-onset widespread pain within a cohort of newly employed workers.
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- SUBJECTS AND METHODS
- Supporting Information
This is the first study conducted within an occupational setting to examine the relative effects of work-related mechanical, psychosocial, and environmental factors in relation to the new onset of widespread pain. Widespread pain is common in this young, newly employed population, and the risk factors are multidimensional, with work-related mechanical factors and work-related psychosocial factors playing an important role.
In interpreting these findings, there are a number of methodologic considerations. The current study was conducted among newly employed workers to minimize the “healthy worker effect.” Individuals working in well-established work forces may be exposed to different risk factors than those experienced by young, newly employed workers. For example, in the current study, relatively few subjects reported being exposed to adverse work-related psychosocial factors. We did, however, assess whether the healthy worker effect influenced the present findings by investigating the proportion of subjects who changed their job at followup and determining whether such job changes were due to aches or pains. A total of 79 subjects left their baseline occupation during followup, but only 1 of them reported any musculoskeletal symptoms. It therefore seems that the influence of the healthy worker effect in the present study was minimal. However, due to the nature of the jobs in the current study, this cohort may have been healthier than the general population, and some jobs required the completion of rigorous fitness tests prior to employment. Consequently, we may have underestimated the prevalence of new-onset widespread pain in relation to the general population.
Due to the prospective design of the current study, with exposure being measured a year prior to the new onset of widespread pain, we were able to determine the temporal relationship between exposures and outcomes. We made no attempt to ascertain widespread pain status in the intervening months and are therefore unable to say anything about the new-onset rate during this time. However, this does not affect the internal comparisons between predictors and outcomes. Misclassification of pain status at followup may have made it more difficult to detect an effect. Changes in exposure may also have occurred in the intervening months. The suitable length of time over which to measure exposures, particularly work-related psychosocial exposures, is something that has recently been debated (19). We assessed interactions between the followup period and predictor variables to determine whether the relationship between exposures and outcomes had changed during the followup period. We found that the relationship had not changed significantly for any of those variables included in the final predictive model.
The outcome ascertained in this study was widespread pain, which was defined according to the ACR guidelines used for the classification of fibromyalgia. Estimates of chronic widespread pain in the general population have been reported to be in the region of 10–13% (20–22), but we did not identify any studies conducted within the work place. Previously, we found that the majority of individuals who report widespread body pain have experienced their pain for 3 months or longer (20).
The “new prevalence” rates observed in this study of young, presumably healthy, workers was high. Furthermore, a substantial proportion reported that their pain had limited their normal activities, either at work or at home (27% at 12 months and 31% at 24 months). Nevertheless, the proportion of these subjects with chronic pain is likely to be smaller, and it is unlikely (although not investigated) that more than a very small proportion would be positive for the other features, such as tender points, necessary to classify their condition as fibromyalgia. In addition, the prevalence of widespread pain at baseline was more common in men, whereas chronic widespread pain and fibromyalgia tend to be much more commonly reported in women. Thus, we caution that the high prevalence rates we obtained should not be taken as an indication of severe morbidity. Despite this, it is thus of substantial interest that work place psychological factors should show the positive associations observed. It would be necessary to undertake longer-term followup of these subjects to determine whether such factors have a similar, or even enhanced, role in predicting the future development of disabling, chronic widespread pain of the nature of fibromyalgia.
The work place exposures we analyzed may not have been typical of a normal working day. However, in an attempt to assess this and in response to a direct question, we found that the majority of individuals reported that the demands of the last working day were much the same “as usual” (78% and 92% at 12 and 24 months, respectively). Importantly, the proportion of subjects reporting demands as being less physically demanding or more physically demanding during the last working day did not differ according to pain status at followup.
We have found within this population, as with other study populations, that monotonous work is one factor that consistently predicts new-onset musculoskeletal pain (10, 23). Although monotonous work could be a marker of repetitive tasks, such as movements of the arms or wrists, it was found to be independently predictive. Monotonous work may lead to increased psychological job stress, which might explain adverse health outcomes, including the onset of musculoskeletal pain (18). Another possible explanation is that subjects who perceive their work as monotonous or boring have a lower pain threshold than those who do not perceive their work in the same way. Other investigators observed a trend toward an increasing prevalence of fibromyalgia in association with increasing levels of physical work stress, but not mental stress (5). However, that study was cross-sectional, which makes it difficult to establish the temporal relationship and introduces the possibility of recall bias. It also was not clear how levels of physical and mental stress were measured.
More recently, we examined the relationship between work place factors and the new onset of chronic widespread pain among an unselected population sample (6). As in the current study, the risk of the new onset of chronic widespread pain was found to be multifactorial, with the strongest associations for repetitive movements of the wrists, other regional pain symptoms, and individual psychosocial factors, in particular, illness behavior. However, that study was conducted among a stable work force, with the majority of subjects (95%) being in the same employment for the previous 36 months. In addition, job histories were collected retrospectively and may have been influenced by recall bias. Furthermore, that study did not include as extensive measurements of work-related risk factors as those collected in the current study. In that study, however, as in the current study, we did not measure major physical trauma (e.g., work place accidents), which have been implicated in the onset of widespread pain syndromes (3, 4). Our conclusions are restricted to low-grade work-related trauma.
The current study has potential implications for interventions designed to prevent the new onset of widespread musculoskeletal pain in the work place. Such studies are currently limited. One small study of fibromyalgia patients (n = 86) found no difference in the job difficulty subscale of the Fibromyalgia Impact Questionnaire in 3 groups of subjects (control, education, and education plus physical therapy) (24). Further research is required to investigate the effectiveness of work-related psychosocial interventions, for example, reducing the perception of monotonous work may be achieved through more-frequent job rotation or more-varied work tasks, whereas increased social support may be achieved through more contact with line managers or availability and accessibility to occupational health professionals.
In summary, this study is the first to examine the relationship between work-related mechanical, psychosocial, and environmental factors and the new onset of widespread pain in a cohort of newly employed workers. We demonstrated that the new onset of widespread pain is common and the risk is multifactorial. The strongest independent predictors of symptom onset were, however, work-related psychosocial factors, and these associations have implications for the development of possible interventions.