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Fibromyalgia syndrome (FMS) is a chronic musculoskeletal pain disorder. Although pain is the primary chronic symptom, disturbed sleep is also a major symptom of patients with FMS. Patients report difficulty falling asleep, significantly more nighttime awakenings, and unrefreshing sleep (1). The majority of sleep research in patients with FMS focuses on the quality of sleep, because the amount of sleep does not appear to differ between FMS patients and healthy subjects (2). Analysis of electroencephalograms indicates that patients with FMS take longer to fall asleep and have frequent arousals, extended stage 1 sleep, and little slow wave sleep (1), which may indicate a vigilant arousal state during sleep (3). Furthermore, when depressed, patients with FMS report lower levels of activity and increased sleeping during the day, and significantly more sleep interruptions and movement at night (4).
Sleep problems have been related to both depression and pain among patients with FMS in numerous studies (3); however, the direction of these relationships is not yet well established. The Neuromatrix Theory of Pain (5) suggests that pain is impacted by multidimensional factors, including psychological and general health characteristics of individuals. Sleep problems, which fit into the general health characteristics construct of the theory, may impact the neuromatrix through their negative effects on other systems, such as the immune system. Support for this theory comes from research suggesting that sleep may impact the neuromatrix through its effects on intervening systems. For example, lack of sleep leaves individuals more susceptible to infection (6), elevated resting blood pressure and decreased muscle sympathetic nerve activity (7), and increased activity of the autonomic nervous system (8). Specific to FMS, research suggests that good sleep quality may moderate the relationship between affect and pain (9). Essentially, a good night's sleep increases our ability to resist bouts of pain; poor sleep, on the other hand, especially when chronic, may increase our vulnerability to symptoms.
Nicassio and Wallston (10) evaluated the relationship between sleep problems, pain, and depression over 2 years among patients with rheumatoid arthritis. Their longitudinal analyses indicated that sleep problems did not predict subsequent pain, but pain predicted subsequent sleep problems. In addition, sleep problems did not predict subsequent depression, but pain did.
Affleck et al (11) investigated the temporal sequence of pain and sleep problems among a sample of patients with FMS over a 30-day period, using handheld devices to record sleep quality in the morning and pain throughout the day. Their findings suggested that sleep difficulties the night before predicted increased pain during the day, but daily measures of pain did not predict poorer subsequent sleep.
The difference in findings between Affleck et al (11) and Nicassio and Wallston (10) may have occurred because they studied different patient populations. Sleep may very well be an etiologic factor for FMS symptoms, but not for symptoms in other rheumatic conditions. This was investigated by Moldofsky and Scarisbrick (12), who altered the sleep pattern of 6 healthy subjects to imitate those of FMS patients. All subjects subsequently reported symptoms similar to those reported by patients with FMS. Their study suggested that poor sleep may have a significant effect on the development or exacerbation of FMS symptoms and paved the way for future studies of sleep in patients with FMS.
In the present study, we examined sleep, pain, depression, and physical functioning at baseline and 1 year later among patients with FMS. Because they used a similar research design, we built on the work of Nicassio and Wallston (10) by using a path analysis approach; however, because our sample consisted of FMS patients, we hypothesized that our findings would match those of Affleck and colleagues (11), in that baseline sleep would predict subsequent pain. We also predicted that both sleep and pain would predict subsequent depression. We had no specific prediction for physical functioning because this variable has not been examined in relation to sleep in the literature.
- Top of page
- PARTICIPANTS AND METHODS
- AUTHOR CONTRIBUTIONS
As hypothesized, our findings agree with those of Affleck et al (11), in that sleep precedes pain in fibromyalgia, even with different methodologies and time measures. Whereas Affleck et al (11), using ecological momentary assessment over a 1-week period, found that sleep predicted pain in patients with FMS, the present study, using traditional self-report measures of pain at 2 points during a 1-year period, reached the same conclusion.
This longitudinal study suggests a causal sequence of symptom impact. Specifically, in the present model no baseline variable predicted 1-year sleep, baseline sleep predicted 1-year pain, baseline pain predicted 1-year physical functioning, and baseline physical functioning predicted 1-year depression. Clearly, sleep problems among patients with FMS impact symptoms in the long term and deserve more attention both in research and in clinical practice, because they seem to initiate a cascade of symptoms that lead to depression, a serious and prevalent problem in this population. The importance of sleep in the symptomatology of FMS has been identified by sleep researchers as well (2). However, the present study measured these variables over 2 time periods, measuring baseline predictors of 1-year outcomes instead of various and continuous time periods. Therefore, it is not clear whether these findings truly reflect what would be seen over time if these participants were followed for longer periods and measured repeatedly.
Only 1 previous study with a small sample size (n = 16) has reported detailed information on the sleep quality of patients with FMS (28). Our larger sample provides greater support for generalizing findings regarding the characteristics and effects of sleep quality among patients with FMS. Although sleep quality was significantly better at the 1-year assessment, it remained poor, indicating poor sleep may be a chronic problem, with dysfunction during the day showing no improvement. This is further supported by literature indicating that, despite receiving 6–8 hours of sleep, patients with FMS wake up stiff, fatigued, and in pain (29). This suggests that improving sleep quality in this population would decrease pain, possibly also impacting functioning and depression, and that the focus should be on quality of sleep, not quantity.
For depression, pain, and sleep, patients improved by the 1-year assessment. We considered whether these improvements were related to the intervention. The intervention consisted of a social support group, a social support and education about FMS group, and a no treatment control group. However, the intervention groups did not differ from the control group in any of these variables, i.e., the changes in symptoms occurred in the presence of, but not because of, the intervention. Although these findings could represent a simple regression to the mean and should be examined in further research, our findings are consistent with those of other studies indicating that, although FMS symptoms may decrease in severity (30), patients still score within clinical ranges across time (1, 31).
These conclusions do not hold as strongly for depression in this sample. The improvements in depression at followup were noteworthy, both as overall means and as proportions that scored above and below the clinical cutoff. Although almost 50% of participants scored at the depressed range at baseline, that percentage dropped to 30.5% at 1 year. Although the rates remained high, this drop is both statistically and clinically significant. It could be that there was a placebo effect, because all participants were in a research study. Also noteworthy was the role of depression in the path model; specifically, baseline depression did not contribute to pain, physical functioning, or sleep at 1 year. Our findings suggest that depression may be the end result of a process that begins with sleep problems.
Interestingly, physical functioning did not change from baseline to the 1-year assessment as the other variables did. Scores were consistently average (∼1.7 out of a 4-point scale) at baseline and 1 year. Furthermore, only baseline pain predicted physical functioning at the 1-year assessment, with a very small effect size. Physical functioning did predict depression in this sample. This finding was not surprising, although it was not hypothesized. Research has suggested for some time that physical disability predicts later depression (32). The model of depression by Lewinsohn et al (33) suggests that circumstances that disrupt adaptive functioning increase vulnerability to depression. For instance, the individual may be more susceptible to depression as a result of not being able to engage in valued activities such as self-care.
When interpreting these results, it is important to keep in mind that our sample was highly educated and mostly white. Therefore, generalizing these findings to other populations entails some risks. Also, this sample reported elevated levels of sleep disturbance. Therefore, it would be difficult to determine whether similar results would be elicited in a sample with varying levels of sleep quality. The present study used self-report measures to assess depression, pain, and sleep. These measures may not reflect the symptoms as accurately as objective measures, although subjective reports of sleep quality have been corroborated with objective data for this population (34). Future studies would benefit from including objective measures of these variables. Some studies have used electronic sleep diaries (9, 11) or actigraphy (2, 34) to study FMS pain and sleep. However, this methodology becomes more difficult when studying larger samples over a longer period of time. Also, all measures assessed symptoms over the past week except for the sleep measure, which assessed symptoms over the past month. This difference in measurement may result in discrepancies, because symptoms may have been very different over the past month and in the past week. However, the correlations between sleep and other variables were similar to those among other indices of symptoms. Finally, all findings should be interpreted with caution, given the long time frame between both assessments. It is possible that there were fluctuations in each variable that were not captured by the 2 assessment periods, instead of a gradual increase or decline suggested by the data. Future studies should attempt more frequent assessments to gain a better understanding of the course of these problems.
Alternately, a strength of the present study was the large sample that was followed over time. Our design allowed us to include more variables than smaller studies because the latter have lower power. Therefore, the present study was able to determine the impact of the main study variables in the presence of relevant demographic and disease variables. In conclusion, the present study highlights the importance of further research in sleep among this patient population, given the findings of the path model.