In the United States (U.S.), chronic health conditions are a leading cause of death and disability [1
], and the prevalence of chronic illness is expected to continue to increase as the general population ages [2
]. A recent Milken Institute analysis revealed that in 2016, the total direct and indirect costs of chronic disease were $
3.7 trillion dollars, which is almost 20% of the U.S. economy [3
Fibromyalgia syndrome (FM) is a chronic musculoskeletal pain condition that is often accompanied by fatigue, headaches, sleep disturbances, memory, and mood difficulties [4
]. Two to four percent of the U.S. population is affected by FM, and it is more often diagnosed in women than men, with a previously reported 1:9 male to female ratio [5
]. Even though it can develop at any age, the highest prevalence was found in the 50–59 age group [6
]. The etiology of FM is unknown, with no agreed-upon biological markers, and the treatment focus is on symptom management that incorporates drug and non-drug practices [8
Osteoarthritis (OA) is a chronic degenerative joint disease that occurs when the cartilage between the bones deteriorates. As a result, people with OA often experience joint pain and irritation of adjacent bone tissue [9
]. In the U.S., OA is the most common form of arthritis and affects approximately 32.5 million people [10
]. It is associated with aging, with the highest prevalence in people over 60 years old, while other risk factors include being female, low levels of education, obesity, having a genetic predisposition, and joint overuse or injury [10
FM and OA are prevalent chronic pain conditions with high associated health care costs [13
]. Despite clinical variations and different etiology, OA and FM share common neural pathways involved in pain and tenderness processing, as well as similar central sensitization to pain [15
]. Furthermore, FM is frequently misdiagnosed as OA because of symptom similarities, such as morning stiffness and muscle pain [17
]. Additionally, the treatment of both conditions requires self-management techniques and effective coping strategies [17
]. Comparing these two chronic painful disorders has been suggested as a way to establish the reference point of the illness impact of both FM and OA [20
As with other chronic conditions, people with FM and OA often experience psychological difficulties and report higher rates of depression than those in the general population [21
]. To study depression in people with these illnesses, researchers have investigated various health, psychological and demographic predictors of depression [26
Using both general and disease-specific metrics, researchers have found that higher impact of the disease predicted higher depression scores in people with OA and FM [32
]. Specifically, pain and limited functioning were associated with depression in OA and FM [33
]. While individuals with FM consistently reported higher disease impact than individuals with OA [37
], it is unknown to what extent changes in health status impact depression in these conditions.
When examining the association between psychological variables and depression, researchers have found that higher levels of self-efficacy and lower levels of helplessness predicted lower depression in people with FM [38
]. Although there are fewer studies examining the direct impact of these psychological factors on depression in people with OA, researchers found that self-efficacy predicted favorable post-surgery outcomes and was linked to reduced disability, while surgery and disability were independently associated with depression [42
]. Additionally, Cronan and Bigatti [48
] found that women with FM had significantly higher levels of helplessness and depression than women with OA.
Specific demographic characteristics have also been associated with depression in people with FM, such as being female, not married, young, being from a minority group, low socioeconomic status, and low levels of education [30
]. Several demographic variables have been shown to predict depression in people with OA. For example, younger adults with OA reported greater depression than older adults [50
]. Sale et al. [27
] reported that being female predicted higher levels of depression in a sample of 1227 OA patients, even after controlling for negative life events.
Among those with FM, concurrent depression negatively impacted quality of life and resulted in significantly higher health care costs than those with FM who were not depressed [51
]. At the same time, in people with OA, concurrent depression can adversely affect surgical outcomes, increase drug prescription and the use of health care services, as well as decrease adherence to a treatment regimen [53
Even though researchers found that patients with FM reported greater depressive symptomatology than OA patients [26
], fewer studies have compared predictors of depression in people with FM and OA [54
]. In our lab, independent studies were conducted in which the effects of social support and education intervention were investigated for people with OA and FM. However, the important question of whether the predictors of depression were different for these two populations, with data gathered at baseline, have not been addressed. Given the burden of depression on people with FM and OA and the shared similarities between the two conditions, determining whether the predictors of depression differ among people with FM and OA may assist in the development of more effective treatment strategies and more timely interventions, determine whether the interventions should be different for each condition, and elucidate the mechanisms of depression among those with OA and FM.
The purpose of the present study was to investigate whether the predictors for depression differed for people with OA and FM. The predictors included demographics variables (i.e., age, gender, education, ethnicity, and income), health variables (i.e., quality of well-being, Body Mass Index (BMI), and disease-specific health), and psychological variables (i.e., helplessness and self-efficacy).
The purpose of the present study was to determine whether the predictors of depression among people with FM and OA differed. Drawing on the biopsychosocial model of depression, we identified a variety of possible predictors of depression and examined the difference between groups. There were several important findings from the present study.
As hypothesized, both health status and disease impact were significant predictors of depression in the present study. Those with worse health status or disease impact had higher depression scores than those with better health status or less disease impact. Participants with FM also had lower health status and higher disease impact than those with OA. There was a significant interaction such that depression was negatively associated with quality of well-being, and the relationship was stronger for FM than for OA. A significant interaction between group and disease impact indicated that people with FM were more affected by their condition than those with OA. This finding is supported by researchers who found that mental health was strongly contingent upon having a healthy physical condition [73
], and an association between depression and level of impairment has also been reported among patients with FM and OA [75
]. However, FM and OA have distinct clinical features and might impact an individual’s health and depression through different mechanisms. For instance, the pain subscale of the AIMS was found to be strongly associated with depression and, when depression was treated, it resulted in a reduction in pain and disease-related disability in people with OA [21
On the other hand, the relationship between pain, disability, and depression in FM remains more complicated. Multiple researchers have found that depressed people with FM were more sensitive to pain than non-depressed FM patients [79
]. However, others have found that depression did not correlate with pain sensitivity, and researchers did not find any cerebral differences in pain processing between depressed and non-depressed FM patients [77
]. They suggested that depressed patients with FM did not experience distorted or augmented pain sensations. However, they found that health status and depression were correlated and, therefore, hypothesized that the mood of individuals with FM might affect the perception of their physical health. In another recent study, pain was not independently associated with quality of life, but other factors such as depression, work status, and activity level were associated with pain [80
]. More studies are necessary to clarify the relationship between health status and depression in the FM population.
The findings from the present study indicated that psychological predictors (self-efficacy and helplessness) were associated with depression in people with FM. Specifically, lower levels of self-efficacy and greater helplessness predicted higher depression scores, and this was particularly true in the FM group. These results are consistent with previous research findings indicating that pain conditions may undermine one’s belief in self-efficacy and, as a result, increase depressive symptomatology [81
]. The findings from the present study were supported by Van Liew et al. [39
], who found that among people with FM, high self-efficacy at baseline predicted fewer symptoms of depression than people with low self-efficacy. They found that individuals who initially had more depressive symptoms were more likely to experience changes in pain intensity at follow-up if their self-efficacy beliefs changed. Buckelew and colleagues [82
] proposed that strong self-efficacy beliefs fostered healthier and more consistent coping mechanisms in FM patients that allowed adjustment to the diagnosis and the management of their symptoms.
Among participants in the present samples, high perceived helplessness predicted higher depression scores, particularly for the FM group. These results are not surprising, given that both self-efficacy and helplessness are conceptually similar constructs that describe the opposite ends of the perceived control spectrum. Helplessness was reported to mediate the relationship between pain and depression with FM and was indirectly linked to subjective well-being through its influence on illness uncertainty [41
]. Individuals with FM were at an increased risk of perceived helplessness because of higher pain, uncontrollability, and the uncertainty of the disease’s etiology and management [79
]. Some researchers have reported that helplessness can result in the adoption of ineffective coping mechanisms and greater depressive symptomatology [85
]. However, although this explanation makes intuitive sense, the correlational and cross-sectional nature of these and our study do not allow the establishment of a causal relationship between helplessness and depression [41
]. It could be argued that feelings of helplessness are direct consequences of depression to which FM patients are predisposed. Future researchers should develop and test interventions to increase a sense of perceived control and reduce helplessness to examine this relationship further.
The results from the present study indicated that participants with FM had significantly higher depression scores than the OA participants across all demographic predictors. Younger participants were significantly more depressed than older participants. In addition, people with lower incomes were more depressed than those with higher incomes. A significant interaction indicated that in the FM group people with lower educational levels had higher depression scores than those with high educational levels; however, there was no difference in the OA group. These findings are consistent with those reported by Güven et al. [30
], who found a negative correlation between total years of education and depression in FM participants. However, in the present study, contrary to previous findings [87
], education did not significantly predict depression in the OA group. A possible, albeit speculative, explanation could be that difficulties related to the unknown etiology and trajectory of FM, as well as the uncertainty associated with the diagnosis, could account for higher depression scores among those with less education. It is also possible that those who are more educated might have an advantage in having more access to high-quality information that provides a buffer for depression. Conversano et al. [89
] provide support for this explanation; in a recent meta-analysis, they found that education about methods for self-management improved treatment outcomes for people with FM. A significant interaction indicated that White participants in the OA group were more likely to be depressed than non-White participants. This finding contradicts previous research reports in which minority participants with OA were found to have higher depression levels [90
]. A possible explanation for this is that ethnic minorities represented only 8% of the OA group, thus creating a statistical limitation. However, in the FM group, White participants were more depressed than non-White participants. Marr et al. [28
] reported similar findings. In their study, they found that racial and ethnic minorities experienced greater depression, mood disturbances, pain, and poorer health than their White counterparts. They hypothesized that minority participants experienced greater distress and depression because of pain and poor health.
There were limitations of this study. Because this was correlational research, no conclusions about cause and effect can be drawn. Another significant limitation was the lack of minority participants. Some researchers have reported that there may be a higher prevalence rate of FM among racial minority women [92
]. Still, more research is needed to determine whether the prevalence rates vary as a function of ethnicity. Even though similar prevalence rates of OA among different racial and ethnic groups have previously been reported, racial disparities in pain perception and function have been observed among older adults with knee OA [93
]. Because of the well-established pain-depression link in OA [21
], discrepancies in depression and the predictors of it should be examined in racially diverse samples. Future studies focused on minority groups are warranted. In addition, the representation of men with FM was small, which limits the generalizability of the findings to men. The male to female ratio among those with an FM diagnosis in the general population was reported to be 1:9 [5
]. However, 95.5 percent of participants in the present FM sample were female; this exceeded the expected prevalence of women in general population. Additionally, while FM and OA are both associated with aging, the findings should be generalized with caution to younger individuals, such as those with juvenile FM or to younger individuals who develop OA as a result of injury. Future research investigating predictors of depression in younger populations with FM and OA is warranted. Furthermore, all the participants came from the same large HMO; there could be differences between those from other health care providers. However, despite these limitations, the number of participants in both the OA and FM groups were large, which increases the likelihood that they represent the populations from which they were drawn.