Of all mental health outcomes associated with persistent pain, depression is by far the most prevalent. Community surveys indicate that approximately 20% of individuals with persistent pain symptoms suffer from a diagnosable depressive condition.30 Much higher rates are seen in specialty pain treatment centers.31,32 There is considerable research indicating that prevalence rates of depressive disorders are higher in cancer patients than in the general population.27,33,34 However, no research has yet to examine prevalence rates of depressive disorders in cancer survivors with persistent pain.
Cancer pain can exert a significant negative impact on emotional functioning.35,36 Higher levels of pain have been associated with reductions in quality of life in long-term cancer survivors.28,37,38 Higher levels of pain have also been associated with more severe depressive symptoms in cancer survivors.39-41 Zaza and Baine42reviewed 19 studies that examined the association between cancer pain and psychological distress. The majority of studies reviewed (14 of 19) revealed a significant association between cancer pain and emotional outcomes such as anxiety, fear, and depression.42
Research in this area has appealed primarily to "diathesis-stress" formulations in efforts to explain how depression might arise following the development of a pain condition.43 Diathesis-stress formulations essentially attempt to explain why some individuals become depressed as a function of their pain experience while others do not.44 These models suggest that depressive symptoms might arise when vulnerability (or resilience) factors (i.e., diatheses) interact with vulnerability-relevant
Figure 1. A Diathesis-Stress Model of Health Outcomes Associated with Pain.
Figure 1. A Diathesis-Stress Model of Health Outcomes Associated with Pain.
contextual factors (i.e., stressors). As shown in Figure 1, diathesis-stress models are not specific to depression, but can be invoked to explain a variety of health outcomes.
Numerous investigations have addressed the role of pain catastrophizing as a determinant of depression and other pain-related outcomes.45-47 Pain catastrophizing has been defined as "a negative cognitive set brought to bear during actual or anticipated pain experience."48 Research has supported a multidimensional conceptualization of catastrophizing, comprising elements of rumination ("I can't stop thinking about how much it hurts"), magnification ("I'm afraid that something serious might happen"), and helplessness ("There is nothing I can do to reduce the intensity of the pain").
Prior to its emergence in the pain literature, catastrophizing had been discussed primarily within the context of cognitive theories of depression. For example, in Beck's49 cognitive model of emotional disorders, catastrophizing is viewed as a "cognitive distortion" that might contribute to the precipitation and maintenance of depressive symptoms. Beck et al.49 proposed that "depressive schema" might become activated following the occurrence of negative life events. Once activated, depressive schema were said to give rise to a variety of cognitive distortions including catastro-phizing, overgeneralization, personalization, and selective abstraction. In Beck et al.'s49 model, cognitive errors are expected to bias information processing in such a manner as to increase the likelihood of the development of depressive symptoms. Adapted to pain, a diathesis-stress model of depression would suggest that the events associated with the onset of pain, or the stressors associated with living with a persistent pain condition might contribute to the activation of depressive schema in vulnerable individuals.43
Bishop and Ward50 examined the relation between pain catastrophizing and various pain-related outcomes in a sample of women who had been diagnosed with breast cancer. On average, women had been diagnosed 5 years earlier, and had been experiencing pain for approximately 18 months. Regression analyses revealed that pain catastrophizing contributed significant unique variance to the prediction of depression and anxiety, even when controlling for other types of coping strategies. In other words, of all the coping strategies assessed, pain catastrophizing emerged as the most important predictor of anxiety and depression.
There are indications that catastrophizing might contribute to a propensity to appraise pain symptoms as a sign of disease progression. Research suggests that 1050% of cancer survivors attribute their pain to disease progression even when in remission.15,51,52 A recent study reported that cancer survivors with high levels of pain catastrophizing were more likely to interpret increasing pain as sign of disease progression than cancer survivors with low levels of pain catastrophizing.52 While cancer survivors tended to attribute their pain as a sign of disease progression, patients with rheumatoid arthritis tended to attribute their pain to exertion. The propensity to interpret pain signals as a sign of disease progression might lead to various adverse emotional outcomes such as depression, anxiety, and fear.53
In other domains of pain research, investigations have highlighted the potential contribution of a number of additional cognitive variables to the development or maintenance of depression. Appraisal-related variables such as perceived lack of control,53 perceived limitations,54,55 perceived interference due to pain,56,57 perceived inadequacy of problem-solving skills,58,59 and cognitive distortions60,61 have been associated with elevations of depressive symptomatology in patients with persistent pain.
The results of numerous investigations suggest that self-efficacy for managing pain54,62 might represent a protective or resilience factor against negative pain-related outcomes. In pain research, self-efficacy has been defined in terms of one's overall confidence in the ability to deal with symptoms, stresses or limitations associated with a pain condition.63,64 Considerable research has addressed the relation between self-efficacy and pain-related outcomes in patients with arthritic conditions (e.g., rheumatoid arthritis, osteoarthritis, fibromyalgia).28,65 High levels of self-efficacy are thought to impact on emotional functioning by promoting the use of coping strategies, increasing the range of activities individuals will undertake and by increasing the effort invested in activity.66 The role of self-efficacy as a determinant of psychological and physical functioning in cancer survivors with persistent pain has yet to be systematically studied.
There is research to support relation between the use of pain coping strategies and pain-related outcomes in cancer survivors. Pain coping strategies are the various cognitive techniques or behaviors that individuals might use to manage the stresses associated with persistent pain.46,67 In their efforts to cope with their pain, individuals might use "active" coping strategies such as problem-solving or distraction, or they mightuse "passive" coping strategies such as resting or activity avoidance.68,69 Bishop and Ward50 found that breast cancer survivors who used more active pain coping strategies also reported fewer depressive symptoms and fewer functional limitations due to pain.
There are indications that patients with cancer pain use fewer pain coping strategies than patients with chronic non-cancer pain. Dalton and Feuerstein70 reported that, compared to chronic non-cancer pain patients, patients with cancer pain obtained lower scores on a measure of coping. Cancer pain patients also reported using more pain medication than chronic non-cancer pain patients. Cancer pain patients did not report more pain-related fears than chronic non-cancer pain patients.70
Other investigators have commented that comparisons of pain experience between individuals with cancer pain and chronic non-cancer pain reveal more similarities than differences.71 The results of investigations showing similarities in the pain experience of cancer survivors and patients with non-cancer pain conditions suggest that interventions that have benefited individuals with non-cancer pain might also benefit the cancer survivor with pain.28,71
There has been growing interest in the relation between acceptance and adjustment to persistent pain.72 McCracken and his colleagues have discussed acceptance as protective or resilience factor that might decrease susceptibility to depression in individuals with persistent pain.73 In this context, acceptance has been defined as "an active willingness to engage in meaningful activities in life regardless of the experience of pain-related sensations, thoughts, and related feelings that might otherwise hinder such engagement."73 In one study, higher scores on a measure of acceptance were associated with fewer depressive symptoms and lower levels of psychosocial and physical disability.74 The degree to which acceptance contributes to resilience to depression or other pain-related outcomes in cancer survivors has yet to be systematically investigated.
The "vulnerability-relevant contextual factors" component of a diathesis-stress model of pain in cancer survivors would encompass all the stresses that might be associated with pain including persistent physical distress, treatment experiences, treatment phase, loss of employment, loss of financial security, loss of independence, disrupted family relation, etc.38,75-77 In the bulk of research conducted to date on the health and behavioral health outcomes associated with pain, the presence of "vulnerability-relevant contextual factors" has been assumed more than it has been measured and there have been few tests of the hypothesized interaction between vulnerability factors and vulnerability-relevant contextual factors.43,78
Fatigue may represent an important vulnerability-relevant contextual factor in cancer survivors with persistent pain. It has been noted that symptoms of pain, fatigue, and depression appear to cluster in cancer survivors.79 It has been suggested that the nature, severity, and impact of fatigue on the life of the cancer survivor is not well understood.79,80 Fatigue overlaps to some degree with depression, and might be misattributed to a depressive state. Given that the task of coping with cancer pain is resource demanding, the cancer survivor with significant symptoms of fatigue might be particularly vulnerable to the adverse effects of persistent pain on mood and quality of life. Fatigue may interfere with the ability to participate in social and recreational activities that might otherwise act as a buffer to the stress and strain of living with pain. Clinical researchers have called for greater attention to the study of development and trajectory of fatigue symptoms associated with cancer
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