FOR PROOFREADING ONLY

Journal of Behavioral Medicine, Vol. 27, No. 1, February 2004 ( C 2004) Pain-Related Anxiety in the Prediction of Chronic Low-Back Pain Distress Kevin E. Vowles, 1,4 Michael J. Zvolensky, 2 Richard T. Gross, 3 and Jeannie A. Sperry 3 Accepted for publication: May 17, 2003 This study evaluated the relation of particular aspects of pain-related anxiety to characteristics of chronic pain distress in a sample of 76 individuals with low-back pain. Consistent with contemporary cognitive behavioral models of chronic pain, the cognitive dimension of the Pain Anxiety Symptoms Scale (PASS; McCracken, Zayfert, and Gross, 1992, Pain 50: 67 73) was uniquely predictive of cognitive-affective aspects of chronic pain, including affective distress, perceived lack of control, and pain severity. In contrast, the escape and avoidance dimension of the PASS was more predictive of behavioral interference in life activities. Overall, the findings are discussed within the context of identifying particular pain-related anxiety mechanisms contributing to differential aspects of pain-related distress and clinical impairment. FOR PROOFREADING ONLY KEY WORDS: chronic pain; pain-related anxiety; low-back pain. INTRODUCTION Chronic low-back pain is perhaps the most common and disabling of the pain conditions, resulting in significant personal, social, health, and occupational impairment (Nachemson, 1992). In an illustrative example, the incidence of low-back pain in North America alone is approximately 10%, 1 Department of Psychology, West Virginia University, P.O. Box 6040, Morgantown, West Virginia 26506-6040. 2 Department of Psychology, University of Vermont, Burlington, Vermont 05405-0134. 3 Oasis Occupational Rehabilitation and Pain Management, P.O. Box 4013, Morgantown, West Virginia 26504-4013. 4 To whom correspondence should be addressed; e-mail: kvowles@mix.wvu.edu. 77 0160-7715/04/0200-0077/0 C 2004 Plenum Publishing Corporation

78 Vowles, Zvolensky, Gross, and Sperry with a substantial percentage of these persons being unresponsive to traditional medical interventions (Frymoyer, 1993). Perhaps not surprisingly, the cost to the health care system is immense, resulting in over $50 billion in direct and indirect costs each year (Frymoyer, 1993; Hoffman et al., 1993; Nachemson, 1992; Tollison et al., 1985). Historically, low-back pain conceptualizations have been dominated by the medical model in which pain is proportional to identified pathology (e.g., tissue damage). Unfortunately, such a perspective has not contributed to a better understanding of the complex nature of chronic pain nor the underlying processes involved with pain-related disability (Turk, 1990). Accordingly, to better account for the highly varied individual expression of chronic lowback pain, contemporary cognitive behavioral models portray the condition as a sensory-affective response, involving physiological, cognitive, and behavioral components (Waddell, 1987). Within this context, researchers have begun to focus their scientific efforts to understanding the nature of chronic low-back pain at the psychological level of analysis, and pain-related anxiety has been highlighted as one of the most disabling aspects of the chronic pain experience (Lethem et al., 1983; Turk and Okifuji, 2002; Vlaeyen and Linton, 2000). Specifically, heightened levels of anxiety about pain are believed to contribute to avoidance of activities that are perceived to promote pain, which in turn, often lead to physical deconditioning, secondary behavioral problems (e.g., weight gain), and reduced social contact (Hadjistavropoulos and LaChapelle, 2000). Moreover, this pattern of responding is likely to become cyclical in nature, such that emotional responsivity and physical deconditioning lead to greater levels of severe pain, behavioral interference, perceived lack of control over life activities, and affective distress (Asmundson, 1999; Asmundson et al., 1997; McCracken, 1997). In this model, then, anxiety about pain is a critical psychological factor involved with the production of maladaptive responding, behavioral interference, and emotional distress. Despite the general theoretical promise of fear-avoidance conceptualizations of chronic pain (Arntz and Peters, 1995; Craig, 1994; Jensen et al., 1994), researchers have only relatively recently began to systematically explore the association between anxiety about pain and clinically relevant dimensions of chronic low-back pain. This research has been facilitated by the development of valid and reliable methodologies that can assess various aspects of anxiety about and fear of pain (e.g., Kori et al., 1990; McNeil and Rainwater, 1998; Vlaeyen et al., 1999; Waddell and Main, 1984). The Pain Anxiety Symptoms Scale (PASS; McCracken et al., 1992), which assesses four dimensions of pain-related anxiety, including fearful pain appraisals,

Pain-Related Anxiety 79 cognitive symptoms, physiological symptoms, and escape and avoidance behavior, represents one of these methods. Consistent with fear-avoidance models of chronic pain (e.g., Asmundson et al., 1999; Lethem et al., 1983; Vlaeyen and Linton, 2000), research using the PASS has found that patients with chronic pain disorders demonstrate greater pain-related anxiety relative to matched comparison groups, over predict the intensity of pain, cope poorly with pain sensations (e.g., avoidance of physical activity), and evidence greater somatic reactivity in anticipation of pain-eliciting physical activity (McCracken et al., 1993a, 1998; Zvolensky et al., 2001). The PASS total score is also positively correlated with measures of general anxiety, pain, and self-reported disability (Crombez et al., 1999; McCracken et al., 1992), as well as nonspecific physical complaints (McCracken et al., 1998). Furthermore, Burns and colleagues reported that physical ability, as indexed by one s ability to lift or carry certain amounts of weight, was negatively related to scores on the PASS (Burns et al., 2000). Taken together, the PASS has proven to have strong relations with many aspects of the chronic pain experience, especially cognitive aspects of fear and pain (cf. physiological, Crombez et al., 1999). The importance of PASS scores is further supported by their strong relation to treatment outcomes in chronic pain, independent of other theoretically relevant factors such as depressive symptoms and physical ability (McCracken et al., 2002; McCracken and Gross, 1998). Given the existing literature supporting the utility of the PASS, it remains important to evaluate whether specific components of the PASS predict the clinically- and theoretically-relevant dimensions of pain severity, behavioral interference, perceived lack of control over life activities, and affective distress explicitly highlighted in chronic pain models (e.g., Arntz and Peters, 1995; Asmundson, 1999; Vlaeyen et al., 1999). Although the total score has been widely used as an index of fear of pain, the utility of the subscale scores and their relation to aspects of chronic pain is relatively unexplored. To address this issue, this study evaluated the relation of the different subscales of the PASS with established indices of chronic pain distress (i.e., behavioral interference, perceived lack of control, affective distress, and pain severity; Coft et al., 1995), as well as other theoreticallyrelevant variables of pain duration, surgical history, lumbar range of motion, sensory experience of pain, and demographic variables. Consistent with contemporary cognitive-behavioral models of chronic pain (Asmundson, 1999) and anxiety-related disorders (Clark et al., 1989; Eifert et al., 1999), it was hypothesized that cognitive symptoms dimension of the PASS would be uniquely predictive of cognitive-affective aspects of chronic pain. In contrast, the escape and avoidance dimension of the PASS would be more

80 Vowles, Zvolensky, Gross, and Sperry predictive of behavioral interference in life activities because of the pain condition. METHOD Participants Participants were 76 consecutive chronic low-back pain patients. In total, 33 (43.4%) females and 43 (56.6%) males, ranging in age from 21 to 58 (Mean age = 40.4 years, SD = 8.7 years). All participants were Caucasian and had a prolonged history of chronic pain (Mean duration of pain chronicity = 21.3 months, SD = 12.1 months). Additionally, 100% of the patients were occupationally disabled due to their low-back pain problem. Approximately 75% of the sample had completed at least the equivalent of a high school education. The marital status of the participants consisted of 55.3% (n = 42) being married, 30.2% (n = 23) being separated or divorced, 14.5% (n = 11) being single. Finally, 52.6% (n = 37) of the patients had previously received surgery for their presenting low-back problem. As part of an intake appointment, each participant completed a number of self-report questionnaires, a general medical history, and a physical therapy evaluation. Measures Pain Anxiety Symptoms Scale (PASS) The PASS (McCracken et al., 1992) is a 40-item self-report measure in which respondents indicate anxiety related to pain on a 6-point Likert-type scale ranging from 0 (never) to 5 (always). The summation of individual items allows the derivation of a total score and four subscale scores. The content of the four subscales includes (a) cognitive anxiety symptoms related to the experience of pain, (b) escape and avoidance responses related to reducing pain, (c) fearful appraisals of pain, and (d) physiological anxiety symptoms related to pain. The measure has demonstrated good internal consistency across items, with reported alpha s ranging from 0.74 to 0.94, and excellent 2-week test retest reliability, all r s 0.93, with the exception of the escape/avoidance subscale, which had an r = 0.77 across different administrations (McCracken et al., 1992, 1993b). Finally, the validity of the four subscale scores is supported by significant positive correlations with measures of general anxiety, pain, and disability (McCracken et al., 1992).

Pain-Related Anxiety 81 Multidimensional Pain Inventory (MPI) The MPI (Kerns et al., 1985) is a well-established three-part measure that assesses pain appraisals, pain severity, impact of pain on specified life domains (e.g., work), and particular behaviors that are performed as a result of the pain. The MPI has demonstrated adequate reliability and validity in chronic pain populations (Kerns et al., 1985). As is typical of research in this area, in the present study we utilized Section I of the MPI. This segment of the instrument assesses the conceptually- and clinically-relevant domains of pain severity, life control, affective distress, and behavioral interference due to pain. Within each subscale, reported interitem reliabilities have ranged from 0.68 to 0.90 (Ferrari et al., 2000; Kerns et al., 1985), and 2-week test retest reliabilities range from 0.62 to 0.91 (Kerns et al., 1985). McGill Pain Questionnaire-Short Form (MPQ-SF) The MPQ-SF (Melzack, 1987) is a self-report measure that assesses sensory and affective aspects of a pain problem. Ratings are made on a 4- point Likert-type scale, ranging from 0 (none) to 3(severe); items are added together to derive a total score, as well as sensory and affective subscales, which assess specific components of the pain experience. The psychometric properties of the MPQ-SF are well established (see Melzack and Katz, 2001 for a review); reported 15- and 30-day test retest reliabilities range from 0.58 to 0.92 (Burckhardt and Bjelle, 1993; Georgoudis et al., 2001) and internal A1 consistency is adequate (Cronbach s α = 0.71; Georgoudis et al., 2000). In the present study, we used the MPQ-SF sensory scale (total score) rather than a combined sensory and affective total score because the latter may confound the measurement of the sensory experience of pain with pain-related anxiety (Asmundson and Taylor, 1996). Lumbar Range of Motion To provide an index of actual physical movement capacity in the low back, a physical therapist assessed lumbar flexion during a routine physical examination using an inclinometer (possible range: 0 360 ). Although the interrater reliability of physical therapy examinations has been generally low, lumbar flexion has been identified as one of the most reliable measurements with reported interrater reliabilities from 0.87 to 0.93 (Waddell et al., 1992).

82 Vowles, Zvolensky, Gross, and Sperry RESULTS Descriptive Data and Zero-Order Relations Between Predictor and Criterion Variables Means and standard deviations for the psychological variables are presented in Table I. Zero-order correlations were computed between each of the predictor variables and each of the dependent measures to determine the relation between these theoretically relevant constructs. As can be seen in Table II, the results generally indicated that the PASS subscales significantly correlated in a content-specific fashion with the various MPI subscales. In a representative example, the PASS cognitive subscale correlated in the most robust manner with the MPI subscales tapping cognitive-affective aspects of pain-related distress (i.e., affective distress, perceived life control, and pain severity) and to a lesser extent with the MPI subscale tapping behavioral interference. Additionally, divergent validity was demonstrated with the PASS subscales tapping visceral arousal (physiological) and behavioral activation (i.e., escape and fear dimensions) showing a nonsignificant positive relation with cognitive-affective aspects of pain distress. The indices of surgical history, lumbar flexion, and duration of pain problem showed nonsignificant relations with all of the MPI dimensions, reflecting independence of medical/physical parameters associated with functional disability. Table I. Means and Standard Deviations of Predictor and Criterion Psychological Variables Measure Mean (SD) PASS Cognitive anxiety 25.6 (9.9) Escape and avoidance 23.8 (9.2) Fearful appraisals 18.3 (8.9) Physiological anxiety 18.2 (9.8) MPI Affective distress 48.1 (9.1) Behavioral interference 57.8 (8.4) Life control 50.3 (7.9) Pain severity 50.3 (8.2) MPQ-SF 11.8 (7.7) Note. N = 76. PASS: Pain Anxiety Symptoms Scale (McCracken et al., 1992); MPI: Multidimensional Pain Inventory (Kerns et al., 1985); MPQ-SF: McGill Pain Questionnaire-Short Form, sensory scale (Melzack, 1987).

Pain-Related Anxiety 83 Table II. Zero-Order Relations Between Predictor and Criterion Variables Instrument 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 1. PASS (Cognitive) 0.41 0.69 0.58 0.38 0.27 0.51 0.23 0.05 0.18 0.13 0.20 0.01 0.07 0.09 2. PASS (Escape) 0.70 0.48 0.01 0.31 0.00 0.25 0.07 0.13 0.11 0.29 0.08 0.07 0.06 3. PASS (Fear) 0.61 0.21 0.26 0.17 0.23 0.13 0.15 0.08 0.13 0.07 0.08 0.12 4. PASS (Physiological) 0.20 0.21 0.11 0.21 0.05 0.12 0.07 0.30 0.19 0.05 0.01 5. MPI (Affective distress) 0.39 0.40 0.27 0.16 0.16 0.05 0.06 0.06 0.10 0.03 6. MPI (Interference) 0.08 0.26 0.09 0.14 0.00 0.02 0.01 0.08 0.05 7. MPI (Life control) 0.29 0.03 0.14 0.08 0.04 0.08 0.05 0.04 8. MPI (Pain severity) 0.04 0.22 0.26 0.02 0.01 0.06 0.10 9. MPQ-SF 0.04 0.07 0.08 0.10 0.04 0.03 10. Age (years) 0.09 0.02 0.09 0.02 0.11 11. Education (years) 0.09 0.07 0.19 0.06 12. Gender (1 = male; 2= female) 0.07 0.20 0.06 13. Pain duration (months) 14. Surgical history (frequency) 15. Low-back flexion (deg.) 0.24 0.14 0.04 Note. N = 76. PASS: Pain Anxiety Symptoms Scale (McCracken et al., 1992); MPI: Multidimensional Pain Inventory (Kerns et al., 1985). p < 0.05; p < 0.01.

84 Vowles, Zvolensky, Gross, and Sperry Prediction of Pain-Related Distress Hierarchical multiple regression analyses were performed with each of the primary dependent measures. Independent variables were divided into three levels in the hierarchy: (a) demographic variables of gender, age, and education were at level one, (b) medical and physical variables of duration of chronic pain problem, lumbar flexion, MPQ-SF sensory score, and surgery history were included at level two, and (c) PASS subscales at level three. Although demographic, medical, and physical variables were generally unrelated to the subscales of MPI in the present sample, previous investigations have indicated their importance in both chronic pain (Miaskowski, 1999) and pain responding (Carter et al., 2002); therefore, they were included in the present analyses in order to assess the independent value of each of the PASS subscales. First- and second-level variables were entered into the analysis, and the stepwise method was used for third-level variables. For all analyses, partial correlations (Sr) were included to represent effect sizes only for those variables retained in the equation. In terms of the MPI affective distress, the results indicated a significant overall effect, F(1, 76) = 9.9, p.01 (r 2 = 0.12; adjusted r 2 = 0.11). As expected, the PASS cognitive subscale significantly predicted variance in MPI affective distress (β = 0.35, p 0.01, Sr = 0.28), whereas none of the other independent variables added a significant amount of variance in this equation. For the perceived life control dimension of the MPI, there was an overall significant effect, F(1, 76) = 22.2, p 0.001. The r 2 for this equation was 0.24 (adjusted r 2 = 0.23). As hypothesized, the PASS cognitive subscale significantly predicted variance in MPI perceived control (β = 0.48, p 0.001, Sr = 0.54). The PASS fear appraisal subscale was the only other variable to significantly contribute to this equation (β = 0.29, p 0.01, Sr = 0.18), adding an additional 5% of variance (adjusted r 2 change 0.04). For the behaviorally-oriented domain of life interference on the MPI, the results indicated a significant effect, F(1, 76) = 9.2, p 0.01 (r 2 = 0.11; adjusted r 2 = 0.10). As hypothesized, the PASS escape subscale was the only variable to significantly predict variance in behavioral interference (β = 0.34, p 0.01, Sr = 0.22). Finally, for pain severity dimension of the MPI, the results of the regression indicated an overall significant effect, F(1, 76) = 6.4, p 0.01 (r 2 = 0.09; adjusted r 2 = 0.08). As hypothesized, the cognitive subscale of the PASS predicted a significant amount of variance (β = 0.28, p 0.01, Sr = 0.17). No other independent variables added a significant amount of variance in predicting pain severity.

Pain-Related Anxiety 85 Regression equations were also conducted separately for the two genders and resulted in similar findings. In general, the cognitive subscale of the PASS explained a significant amount of variance in the more cognitive aspects of the MPI and the escape/avoidance subscale was more useful in the prediction of the MPI-Interference scale across both genders. In women, however, the cognitive subscale of the PASS did not explain a significant amount of variance in either affective distress or pain severity. DISCUSSION Persons with chronic low-back pain often demonstrate clinically significant levels of anxiety about pain. Such heightened pain-related anxiety is associated with maladaptive coping responses, medication use, and occupational disability (McCracken et al., 1992). Yet, it remains unknown to what extent specific aspects of the global pain-related anxiety construct predict clinically relevant dimensions of chronic low-back pain distress. To address this issue, the present study was designed to evaluate specific pain-related components as differential predictors of established indices of chronic pain distress (Coft et al., 1995) relative to other theoretically relevant variables of pain duration, surgical history, lumbar flexion, sensory experience of pain, and demographic variables. As expected, consistent with contemporary cognitive behavioral models of chronic pain (Asmundson, 1999; Craig, 1994; Vlaeyen et al., 1999), the cognitive dimension of the PASS was uniquely and significantly predictive of affective distress, perceived lack of control, and pain severity. The fear appraisal subscale added a significant, albeit small amount of variance, only for perceived life control. In contrast, the escape and avoidance PASS dimension was significantly predictive of behavioral interference due to pain. This same pattern of findings also was visible when inspecting the zero-order relations between variables. Specifically, there was a greater level of response concordance between cognitive variables and psychological-affective responding to pain, and greater levels of response discordance between psychologicalaffective distress and historical and physical aspects of the pain problem (i.e., surgical history, duration of pain problem, low-back flexion). Such relative response concordance-discordance is a well-established finding in the study of emotion generally (Rachman, 1991) and in studies of pain responding specifically (Craig, 1994). The present study s results extend this result to the fear-avoidance model of chronic pain. Indeed, the results lend further (correlational) support to the perspective that emotional experiences such as pain are best understood as partially independent response systems rather than a more unified construct (Barlow, 1991; Zinbarg, 1998).

86 Vowles, Zvolensky, Gross, and Sperry Overall, these findings are theoretically important to chronic pain models in that they empirically demonstrate a high degree of specificity with the pain-related anxiety construct in a low-back pain population. In particular, the higher the level of correspondence between the particular pain-related anxiety domain and aspects of the pain problem that closely match that fear, the better particular pain indices of distress can be predicted. It is important to note that these findings converge with a larger body of literature in the area of anxiety-related disorders, whereby elevated anxiety is primarily produced when triggered by cues that closely match the object/event of concern (e.g., Clark et al., 1989; Cox, 1996; Eifert et al., 1999; McNally and Eke, 1996). Accordingly, it is becoming increasingly apparent that the specific tendency to respond in an anxious and fearful manner to pain-related events should be more predictive of certain cognitive and behavioral dimensions of chronic pain problems than others. In this way, particular pain-related anxiety components may function as distinct pathways to different aspects of pain-related distress. At a more general level, the results provide additional evidence that psychological variables are important in the prediction of the problematic aspects of chronic low-back pain (Craig, 1994). Indeed, whereas specific pain-related anxiety components predicted pain-related distress, there was no evidence that the duration of chronic pain, surgical history, lumbar flexion, sensory experience of pain, or relevant demographic variables functioned in the same way. Thus, focusing scientific and clinical attention on anxiety and fear of pain is critical to understanding the complex nature of chronic lowback pain. Furthermore, although changes in pain-related anxiety appear to be important in the prediction of multidisciplinary treatments for chronic pain (McCracken et al., 2002; McCracken and Gross, 1998; Vowles and Gross, 2003), it is not yet clear whether reductions in particular pain-related anxiety components are differentially related to other indices of change (e.g., physical capacity functioning). It also is important to note that from a psychometric perspective, the results of this study provide support for the discriminative validity of painrelated anxiety construct as being composed of specific dimensions, as several distinct PASS dimensions varied in their association with chronic pain distress and disability. These findings converge with other research in the area of anxiety pathology, identifying the differential predictive power of specific pain-related anxiety dimensions (Schmidt, 1999). We also found that the PASS and MPI generally share a low, significant (positive) relation with one another, providing convergent validity data for the PASS in a clinical population of low-back pain patients. There are a number of interpretative-related caveats that warrant consideration in this study. First, because the psychological variables were

Pain-Related Anxiety 87 assessed with the same type of methodology, it is possible that the observed findings were, at least in part, due to shared method variance. Future research therefore could employ experimental cognitive methodologies (e.g., Stroop task) to explore more automatic types of processes in which anxiety about pain contributes to emotional distress in low-back pain patients (Mogg and Bradley, 1998). Second, the correlational design while useful at this stage of research development does not permit causal explanations, leaving the results open to a number of alternative explanations in terms of type and direction of the observed relations. Finally, we did not provide a prospective assessment of how pain-related anxiety relates to various aspects of pain distress. Given the present results, in conjunction with other studies in this general area (Asmundson and Taylor, 1996), researchers are in a good position to evaluate the relative stability of the observed findings over time. Taken together, this study evaluated pain-related anxiety, along with other theoretically relevant variables, as predictors of pain severity, affective distress, perceived lack of control, and behavioral interference. Overall, the findings reiterate the importance of anxiety about pain in understanding distress produced by chronic pain problems, and suggest that the higher level of correspondence between the particular pain-related domain and events that closely match that fear, the better problematic aspects of the pain problem can be predicted, and subsequently addressed. REFERENCES Arntz, A., and Peters, M. (1995). Chronic low back pain and inaccurate predictions of pain: Is being too tough a risk factor for the development and maintenance of chronic pain? Behav. Res. Ther. 33: 49 53. Asmundson, G. J. G. (1999). Anxiety sensitivity and chronic pain: Empirical findings, clinical implications, and future directions. In Taylor, S. (Ed.), Anxiety Sensitivity: Theory, Research, and Treatment of the Fear of Anxiety, Erlbaum, Mahwah, NJ, pp. 269 285. Asmundson, G. J. G., Kuperos, J. L., and Norton, G. R. (1997). Do patients with chronic pain selectively attend to pain-related information? Preliminary evidence for the mediating role of fear. Pain 72: 27 32. Asmundson, G. J. G., Norton, P. J., and Norton, G. R. (1999). Beyond pain: The role of fear and avoidance in chronicity. Clin. Psychol. Rev. 19: 97 119. Asmundson, G. J. G., and Taylor, S. (1996). Role of anxiety sensitivity in pain-related fear and avoidance. J. Behav. Med. 19: 573 582. Barlow, D. H. (1991). Disorders of emotion. Psychol. Inq. 2: 58 71. Burckhardt, C. S., and Belle, A. (1993). A Swedish version of the Short Form McGill Pain Questionnaire. Scand. J. Rheumatol. 23: 77 81. Burns, J. W., Mullen, J. T., Higdon, L. J., Wei, J. M., and Lansky, D. (2000). Validity of the Pain Anxiety Symptoms Scale (PASS): Prediction of physical capacity variables. Pain 84: 247 252. Carter, L. E., McNeil, D. W., Vowles, K. E., Sorrell, J. T., Turk, C., Ries, B., and Hopko, D. R. (2002). Effects of emotion on pain reports, tolerance and physiology. Pain Res. Manage. 7: 21 30.

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Queries to Author: A1: Note that the year 1994 in this reference citation has been changed to 1993 according to the reference list. Is it OK? 90