The Helplessness Dimension of Pain Catastrophizing Mediates the Relation between PTSD Symptoms and Pain Rehabilitation Measures

Background Comorbid chronic pain and post-traumatic stress disorder (PTSD) complicate the treatment of both conditions. Previous research has identified pain catastrophizing as a potentially important variable contributing to the relationship between chronic pain and PTSD. However, little is known regarding how the different dimensions of pain catastrophizing—rumination, magnification, and helplessness—uniquely contribute to the relationship between PTSD symptomatology and measures of pain outcome. Methods 491 treatment seeking participants were admitted to a three-week interdisciplinary pain rehabilitation program between July 2016 and March 2020. The patients completed measures of pain severity, pain interference, pain catastrophizing, depressive symptoms, quality of life (QOL), and PTSD symptoms at pretreatment. Results Parallel mediation analyses were conducted to evaluate the mediating effect of the Pain Catastrophizing Scale subscales on the relationship between PTSD symptomatology and pain-relevant variables. The helplessness subscale accounted for significant unique variance in the relationship between PTSD symptomatology and pain severity (b = 0.010, SE = 0.002, 95% CI: 0.006, 0.014), pain interference (b = 0.004, SE = 0.002, 95% CI: 0.001, 0.008), and mental health QOL (b = −0.117, SE = 0.031, 95% CI: −0.179, −0.059), while the rumination and magnification subscales had no significant influence. Conclusions Pain catastrophizing is a multifaceted construct. These results suggest that the helplessness dimension of pain catastrophizing may be the primary target when treating patients with comorbid chronic pain and PTSD symptoms. This study represents the first to evaluate the influence of the individual dimensions of pain catastrophizing on the relationship between PTSD symptomatology and chronic pain outcome.


Introduction
Chronic pain management is often complicated by the presence of comorbid mental health conditions. A growing body of research has demonstrated that posttraumatic stress disorder (PTSD) is highly prevalent among individuals with chronic pain. Evidence suggests that approximately 20 to theory, is based on the notion that symptom reduction is facilitated when maladaptive trauma-related cognitions are challenged through systematic exposure to trauma cues in the absence of feared outcomes [7]. Similarly, conceptualizations of chronic pain theorize that an individual's catastrophic appraisals of an avoidant response to pain promote increased pain severity and functional limitations [8,9]. In both conceptualizations, maladaptive cognitions in anticipation of or response to a feared stimulus (i.e., pain or trauma cue) can result in negative emotional responses that trigger unhelpful patterns of escape and avoidance behavior that have the unintended consequence of reinforcing unnecessary pain or fear-associated impairments.
Conceptual models have been developed that suggest that high rates of comorbidity between PTSD and chronic pain may be accounted for by either a shared vulnerability to onset and/or mutually maintaining factors following onset [6,10]. Te tendency towards interpreting ambiguous trauma-or pain-related stimuli in a catastrophic way is thought to be one factor contributing to the co-maintenance of PTSD and chronic pain [6]. Pain catastrophizing is a cognitive response style characterized by a propensity to view pain as uncontrollable, permanent, and destructive. Te Pain Catastrophizing Scale (PCS) is a psychometrically validated measure commonly utilized in clinical settings to assess patients' tendencies to catastrophize in response to pain [11]. Factor analytic studies conducted on the PCS have identifed three subfactors of pain catastrophizing: rumination, magnifcation, and helplessness [12].
Te research literature has provided some support for the infuence of pain catastrophizing on the relationship between PTSD symptomatology and pain outcome. For example, in a recent cross-sectional study of 203 patients with chronic pain and trauma exposure initiating care in an interdisciplinary pain rehabilitation program, pain catastrophizing (as measured by the PCS) was found to mediate the relationship between PTSD symptomatology and selfreported pain severity and interference [13]. Te mediating efect of pain catastrophizing remained signifcant even after statistically accounting for self-reported depressive symptoms. However, tests of the reverse model (i.e., PTSD symptomatology mediating the relationship between tendency to catastrophize and self-reported pain indices) did not support PTSD symptomatology as a mediator of the pain catastrophizing and pain outcome association. Tus, the connection between PTSD symptomatology and pain outcome was primarily accounted for by pain catastrophizing. To further explore this connection, previous studies have examined the efectiveness of an interdisciplinary pain rehabilitation program in improving pain outcome (e.g., selfreported pain severity and interference) as well as PTSD symptomatology among a cohort of 83 patients with chronic pain and a provisional PTSD diagnosis [14]. Results revealed that patients self-reported signifcant improvements across pain outcomes and PTSD symptomatology. Notably, pre-to post-treatment reductions in pain catastrophizing fully mediated treatment-related improvements in both pain interference and PTSD symptomatology. Tis study provides preliminary evidence for the utility of targeting maladaptive pain-related cognitions to optimize management of both pain and PTSD symptoms in interdisciplinary pain rehabilitation programming.
In summary, accumulating evidence suggests that addressing the catastrophic appraisal patterns of individuals with PTSD and chronic pain may contribute to the efective treatment of both conditions. Further, pain catastrophizing may be an important cognitive construct to consider when examining associations between PTSD symptomatology and pain outcome. However, what is not clear from the existing literature base is how the individual facets of pain catastrophizing identifed within the PCS (e.g., rumination, magnifcation, and helplessness) might diferentially infuence the identifed relationship between PTSD symptomatology and pain-relevant measures, including pain severity, pain interference, depressive symptoms, and quality of life among individuals with chronic pain and trauma exposure. We contend that elucidating the impact of the individual dimensions of pain catastrophizing could further inform modifable treatment targets among the subset of patients seeking chronic pain treatment who experience PTSD symptomatology.
Te aim of this study was to evaluate the infuence of the individual dimensions of pain catastrophizing on the relationship between PTSD symptomatology and chronic pain outcome. We utilized a series of mediation analyses to explore the relative contributions of the three dimensions of pain catastrophizing to the relationship between PTSD symptomatology and relevant pain measures at pretreatment among a cohort of patients with chronic pain and trauma exposure who initiated care in a tertiary-level pain rehabilitation program. Given the exploratory nature of the study, no specifc hypotheses were made related to which dimensions of pain catastrophizing, if any, would mediate the relationship between PTSD symptomatology and painrelated measures.

Participants.
A total of 491 adult patients enrolled in an interdisciplinary pain rehabilitation program between the years of July 2016 and March 2020 who endorsed a Criterion A trauma (i.e., exposure to actual threatened death, serious injury, or sexual violence directly or indirectly) on the PTSD Checklist for DSM-5 (PCL-5) and completed the PCL-5 consented to participate in this study.

Procedures.
Te data were gathered from participants in a group-based, intensive, outpatient, interdisciplinary pain rehabilitation program at the Mayo Clinic. Tis study was approved by the institutional review board of the treatment program, which served as the site of the study. Consecutive referrals who were admitted to the Pain Rehabilitation Center at the Mayo Clinic were eligible for this study. Referrals included a diagnosed chronic pain condition in one or more anatomical sites or fbromyalgia, signifcant painrelated distress and disability, and consent to participate in a pain rehabilitative treatment approach. Additional 2 Pain Research and Management inclusion criteria for this study included an endorsed trauma history and a completed PCL-5. A total of 1249 patients completed care at the Pain Rehabilitation Center during the data collection period. As noted above, 491 (39.3%) met the inclusion criteria for the study. Additional information regarding inclusion and exclusion criteria has been described previously [14]. All participants in the study consented to their data being used in future research projects upon admission into the program. As part of the admission process, participants completed a series of computerized assessment measures (see the Measures section below) and demographic information questionnaires. Previous research has found no diference between paper-and-pencil and webbased administration of commonly utilized measures [15]. All data were collected at the time of program admission (i.e., at a single time point) in this cross-sectional study.

Demographics and Clinical Characteristics.
Demographic and clinical characteristics were collected via a self-report questionnaire. Te demographic characteristics include age, sex, race, marital status, and years of education. Primary clinical characteristics assessed include pain duration and primary pain site.

Pain
Catastrophizing. Te Pain Catastrophizing Scale (PCS) was used to assess maladaptive pain cognitions [12]. Te PCS is a self-report measure that consists of 13 items scored from 0 to 4. Possible scores range from 0 to 52.
Higher scores indicate the individual tends to catastrophize to a greater degree. Te measure consists of three validated subscales: rumination, magnifcation, and helplessness. Te measure has been demonstrated to have robust psychometric qualities [16]. Te internal consistency in the current sample for the total PCS score was high (α � 0.94) and was adequate to high for each of the three subscales: rumination (α � 0.91), magnifcation (α � 0.76), and helplessness (α � 0.90).

Post-Traumatic Stress Disorder Symptoms.
Te PTSD Checklist for DSM-5 (PCL-5) was used to assess the presence and severity of PTSD symptoms. Te PCL-5 is a 20-itemselfreported measure with responders asked to rate how bothersome their symptoms have been in the past month on a 5-point Likert scale (0 � not at all; 4 � extremely). Higher scores indicate greater symptom severity, and a score of 33 or higher is the current clinical cutof for a provisional diagnosis of PTSD [17]. Te measure has been shown to be valid and reliable in quantifying symptom severity and has demonstrated sensitivity to change [17,18]. Te internal consistency for the PCL-5 in this sample was high (α � 0.91).

Pain Severity and Pain Interference. Te West Haven-Yale Multidimensional Pain Inventory (WHYMPI) Pain
Severity and Pain Interference subscales were used to assess the severity and sufering due to pain as well as the impact of chronic pain symptoms [19]. Te pain severity subscale consists of three items, and the pain interference subscale consists of 11 items; both subscales are scored on a sevenpoint scale (0 � not at all; 6 � extreme). Subscale total scores refect the average across the subscale items. Te overall measure has demonstrated strong construct and convergent validity [19,20] with adequate to excellent test-retest reliability [19,21]. Te internal consistency for the Pain Severity (α � 0.72) and Pain Interference (α � 0.88) subscales were adequate to robust for this sample of patients.

Depressive Symptoms. Te Patient Health
Questionnaire-9 (PHQ-9) was used to assess depressive symptoms [22]. Te PHQ-9 is a self-report measure that asks respondents to rate the presence and frequency of depressive symptoms on a four-point Likert scale (0 � not at all to 3 � nearly every day). Higher scores indicate greater symptom severity over the past two weeks. Tis measure has demonstrated sound psychometric properties with high internal consistency and validity [22,23]. Te PHQ-9's internal consistency was adequate for this sample (α � 0.83).

Quality of Life.
Te physical and mental health summary scores of the 36-item Short Form Survey (SF-36) were used to assess physical and mental health quality of life. Te SF-36 consists of two quality of life summary scores, physical and mental health, computed from physical and social functioning, role limitations due to physical and emotional problems, vitality, bodily pain, and general health perception domains. Items and responses are transformed into a coded value ranging from 0 to 100, with lower scores refecting lower health-related quality of life [24]. Te measure has been shown to be reliable and valid [24,25], and further evaluation of the measure has supported the two summary scales as independent constructs of physical and mental health quality of life [26]. Te internal consistency for the physical health summary (α � 0.84) and mental health summary (α � 0.82) subscales within this sample was adequate.

Data Analytic Strategy.
To evaluate the extent to which each of the PCS subscales mediates the relationship between PTSD symptomatology and pain-related outcomes, a series of multiple mediational analyses were conducted. Specifcally, the PCS subscales (e.g., rumination, magnifcation, and helplessness) were entered as mediators in individual models predicting the relationship between PTSD symptoms (i.e., predictor, X) and pain severity, pain interference, physical health-related quality of life, mental health-related quality of life, and depressive symptoms, respectively (i.e., outcome variables, Y). Consistent with prior research [14,27,28], pain severity and depressive symptoms were also included as mediators to account for their efects in the models, except where these variables were the outcome variable. Multicollinearity among mediator variables was assessed by inspecting variance infation factors (VIFs), and results revealed no VIF exceeding 4.03 (range � 1.30-4.03), suggesting this assumption was met. Analyses were conducted with IBM SPSS version 25 using the PROCESS macro [29]. Mediation can be said to occur if the indirect efect (i.e., the relationship between the predictor and outcome variable via the mediator) is signifcant [30]. Signifcance was evaluated using bootstrap estimations for 1000 samples and 95% confdence intervals. An indirect efect is signifcant when the confdence interval does not cross zero. Additional demographic information is found in Table 1, while clinic characteristics of the sample are found in Table 2.

Pain Severity.
A mediational analysis was conducted to evaluate the PCS subscales as mediators in the relationship between PTSD symptoms and pain severity (Figure 1). Consistent with prior studies [13,27,28], depressive symptoms were included in the model to account for the variance attributable to this variable. Results suggested a signifcant total efect on pain severity (c pathway),

Pain
Interference. Next, a mediational analysis was conducted to assess the PCS subscales as a mediator in the association between PTSD symptoms and pain interference ( Figure 2). Depressive symptoms and pain severity were also included as mediators to account for their infuence on pain interference. Tese results suggest that the relationship between PTSD symptoms and pain interference is fully mediated by helplessness, depressive symptoms, and pain severity.

Physical Health-Related Quality of Life.
Te PCS subscales were also evaluated as a mediator of the relationship between PTSD symptoms and physical health-related quality of life ( Figure 3). As before, depressive symptoms and pain severity were included as additional mediators in the model.        3.6. Depressive Symptoms. Finally, the PCS subscales were evaluated as mediators between PTSD symptoms and depressive symptoms ( Figure 5). Pain severity was also included as a mediator to account for its efects. As before, the total efect on depressive symptoms was signifcant (c

Discussion
By evaluating the infuence of the individual validated subscales of the Pain Catastrophizing Scale (i.e., rumination, magnifcation, and helplessness), we were able to elucidate a more nuanced understanding of the psychological facets of pain catastrophizing that mediate the relationship between PTSD symptoms and pain-relevant variables for individuals participating in interdisciplinary pain rehabilitation programming. Te current study, which included 491 patients with chronic pain and an endorsed trauma history, revealed that helplessness signifcantly mediated the relationship between PTSD symptoms, pain severity, pain interference, mental health quality of life, and depressive symptoms, beyond the efects of pain severity and depressive symptoms at program admission. Pain severity and depressive symptoms were also signifcant mediators that helped explain the association between PTSD symptoms and the pain-relevant variables. However, when comparing the relative strengths of the mediators in these relationships, helplessness had a stronger efect on depression compared to pain severity and a stronger efect on pain compared to depression. Interestingly, the other PCS subscales (rumination and magnifcation) were not signifcant mediators in any of the analyses. Te tendency to engage in catastrophic thinking has been long thought to serve as a precursor to PTSD symptoms following the experience of stressful events [31], and individuals with chronic pain and comorbid PTSD are more likely to experience less control over pain, heightened emotional responses to pain, and higher levels of catastrophizing compared to individuals with chronic pain alone [32]. Te fndings are consistent with previous research suggesting pain catastrophizing serves as a potentially important cognitive variable to consider when conceptualizing the relationship between chronic pain and PTSD symptoms [13,14,33]. Furthermore, by utilizing within-subject mediational models, we were able to examine this model in a more granular fashion and isolate the relative contribution of each individual subfactor of the pain catastrophizing construct, with helplessness emerging as the most infuential.
Helplessness due to chronic pain may be conditioned by an enduring pattern of difculties coping with pain symptoms. Past research has shown that helplessness has a unique and signifcant impact on pain severity and disability [34], PTSD symptomatology [35], and the tendency to utilize maladaptive coping strategies for individuals with chronic pain and PTSD [32]. One study found that anticipatory fear and a sense of helplessness were the strongest predictors of PTSD symptoms and predicted 34% of the variance in PTSD symptomatology in individuals with trauma exposure [35]. Terefore, efective treatment for individuals with chronic pain and comorbid PTSD may be best accomplished by implementing therapeutic techniques designed to enhance distress tolerance and decrease experiential avoidance that often leads to perceptions of a lack of control over pain symptoms and anxiety. Tis study demonstrated that the helplessness associated with pain may be the key component of catastrophizing that perpetuates that feedback loop.
It is compelling that the magnifcation and ruminative dimensions of the PCS did not signifcantly mediate the relationship between PTSD symptomatology and pain symptoms or interference, and it is worth exploring. One explanation may be that increased magnifcation and rumination in response to pain and PTSD symptomatology contributes to hypervigilance to physiological symptoms and greater expression of physical and emotional distress [36] whereas magnifcation and rumination of pain may be typical responses of individuals with chronic pain without PTSD, and individuals with endorsed trauma may make eforts to avoid distressing pain-related thoughts or feelings associated with symptom-specifc cues. For example, studies have shown that increased experiential avoidance (i.e., avoidance of coping with thoughts, emotions, or bodily sensations) predicts PTSD and increases PTSD symptoms [37][38][39][40]. Tis avoidance, in turn, may increase a sense of helplessness in the context of pain and PTSD symptoms, accounting for why feelings of helplessness may mediate the relationship between PTSD symptomatology and pain. A second explanation could be the chronicity of pain for participants in this study. Te individuals in the study reported an average pain duration of greater than 12 years. It is possible that early in the course of the chronic pain experience, magnifcation and rumination were more impactful contributors to the pain and PTSD symptomatology relationship. However, as symptoms persist despite eforts to cope, it is plausible that one's perspective may shift to one of helplessness as pain becomes "the new normal" and/or pain has come to be expected with activity. Tese questions merit further empirical investigation, particularly using longitudinal models.
While catastrophizing may be an important process variable, assessing and addressing helplessness for individuals with chronic pain and trauma histories warrant clinical attention following the results of the current study. Education Pain Research and Management regarding helplessness or perceived control in the context of pain-related symptoms, instruction, and practice in cognitive reappraisal of pain-related threat, relaxation training, as well as systematic increases in activity, would likely yield therapeutic beneft for individuals with similar presentations to this sample. Terapeutic programs focusing on cognitive reappraisal and functional restoration have been shown to address catastrophic thinking directly or indirectly [40,41]. Further, research has shown that reductions in catastrophizing can account for improvements in function in activity-based or interdisciplinary pain rehabilitation programming [14,33]. Increases in activity and challenging maladaptive thoughts may increase a sense of self-efcacy in the context of pain, which may directly or indirectly target the helplessness component of pain catastrophizing.
Tere are important limitations when considering the outcomes of the study. First, this study utilized a crosssectional design, and there was no treatment comparison group. Tus, longitudinal and causal relationships cannot be inferred. Second, ethnic and racial diversity was limited within this sample, limiting the ability to draw groupspecifc conclusions regarding diferences or the generalizability of the fndings. Tird, tertiary-level pain rehabilitation care is accessible to a select group of people with the required resources. Terefore, the patterns of fndings from this study may difer for underrepresented groups, who may have higher baseline rates of trauma. Fourth, the timing of trauma exposure in relation to PTSD symptoms and the duration of PTSD symptoms were not assessed. Tis information would improve the ability to examine the relationship between the chronicity of PTSD symptoms and study variables. Fifth, pain avoidance, anxiety sensitivity, and perceived injustice have been shown to be associated with chronic pain and PTSD [42,43]; however, measures of these constructs were not included in this study. Terefore, the current study was unable to evaluate an overall conceptual model of trauma, helplessness, and other painrelevant variables. Sixth, the number of men in the sample was relatively low (23.9%). Lastly, this study did not include measures of possible confounding variables such as emotion regulation capabilities (for example, the alexithymia construct).
In conclusion, the helplessness dimension of the PCS served as a signifcant mediator between posttraumatic stress disorder symptoms and pain severity, pain interference, mental health quality of life, and depressive symptoms above and beyond the contributions of other dimensions of catastrophizing and after accounting for the contributions of pain severity and depressive symptoms. Tese results suggest helplessness assessing and addressing maladaptive cognitions associated with helplessness for individuals with endorsed trauma histories, and chronic pain is of upmost relevance as helplessness may serve as an independent mechanism variable that can infuence treatment outcome. Interdisciplinary pain rehabilitation focusing on functional restoration may be an appropriate treatment context to do so. Future studies evaluating how changes in helplessness impact chronic pain treatment and interdisciplinary pain rehabilitation outcomes are needed.

Data Availability
Te datasets generated and analysed for this study are available from the corresponding author upon request.

Conflicts of Interest
Te authors declare that they have no conficts of interest.