Multimethod assessment of treatment process in chronic low back pain: comparison of reported pain-related anxiety with directly measured physical capacity

Abstract

Although cognitive behavioural treatments (CBT) have proven efficacy in improving symptom management, pain-related distress, physical performance and return to work, few studies have examined the relationship between changes in behavioural process variables during treatment and improvement in outcome variables following treatment. We designed a multimethod assessment strategy to test the relative contribution of changes in physical capacity and pain-related anxiety to treatment outcome variables. Low back pain patients (n=59) were treated with an intensive programme of physical exercise and CBT. Comparisons from pre- to post-treatment showed significant improvement in pain severity, interference, affective distress, activity level, and depression. Improvements in pain-related anxiety were associated with improvements in all outcome variables except interference. Of three physical capacity composite scores, improvement in only one (lumbar extension and flexion capacity) was associated with improvements in all outcome variables except interference. Further analyses demonstrated that the relationship between changes in pain-related anxiety and treatment outcome were independent of changes in physical capacity performance. Changes during treatment in pain-related anxiety may be more important than changes during treatment in physical capacity when predicting the effect of treatment on behavioural outcome measures. These results are discussed in the context of how to improve assessment of the chronic pain patient and improve the effectiveness of multidisciplinary CBT.

Introduction

The results of numerous systematic reviews show that multidisciplinary treatments based on cognitive behavioural principles produce clear benefits for patients with chronic pain. These benefits include improvements in pain, emotional distress, disability, pain behaviour, and coping (Flor, Fydrich, & Turk, 1992; Malone & Strube, 1988; Morley, Eccleston, & Williams, 1999). Multidisciplinary treatments can radically improve return to work rates for patients with chronic pain. Cutler et al. (1994), for example, reported return to work rates of 41–68%. Despite the positive outcomes of multidisciplinary treatments for patients with chronic pain the mechanisms responsible for these outcomes remain obscured. Only a small number of studies have examined the relationship between changes in behavioural process variables and changes in outcome variables brought about by treatment. Data from these types of studies are important as they may lead to treatment packages that are more specific and potent.

A number of studies have examined coping strategies and beliefs about pain as potential treatment process variables. The studies have shown that treatment gains are predicted by changes during the course of treatment, including reduced helplessness (Spinhoven & Linssen, 1991), increased perceived control (Tota-Faucette, Gil, Williams, Keefe, & Goli, 1993; Spinhoven & Linssen, 1991), decreased catastrophizing (Tota-Faucette et al., 1993), and decreased perceived disability (Hildebrandt, Pfingsten, Saur, Jansen, 1997; Lofland et al., 1997; Vendrig, 1999). Jensen and colleagues (Jensen, Turner, & Romano, 1994) studied the role of change in pain-related beliefs and pain coping strategies on the outcome of a multidisciplinary, inpatient pain treatment program. They found that favourable treatment outcome was a product of a decrease in the belief that pain is harmful and disabling, a decrease in praying and hoping, a decrease in catastrophizing thoughts about pain, and an increase in the belief that one can achieve control over pain. Unexpectedly, they found that improvement was not predicted by the changes patients made in their use of the skills targeted during treatment, such as physical exercise, relaxation, and strategies to increase activity.

Burns, Johnson, Mahoney, Devine, and Pawl (1998) examined changes made during treatment in patients' depression, pain-related helplessness, and physical capacity. Treatment included physical therapies and cognitive behavioural treatment (CBT). Based on the results of regression analyses, decreased pain-related helplessness predicted reduced pain independent of variance associated with change in depression. It also predicted decreased downtime independent of change in walking endurance. Increased walking endurance predicted improved daily activity independent of change in helplessness. Interestingly, decreases in pain-related helplessness were correlated with increased walking endurance and accounted for overlapping variance in daily activity and downtime improvements (Burns et al., 1998).

We conducted a study of injured workers with low back pain to test the role of pain-related anxiety in treatment outcome (McCracken & Gross, 1998). All patients participated in a three-week multidisciplinary program including physical rehabilitation strategies and CBT. Results showed that decreased pain-related anxiety significantly predicted improvements in pain severity, depression, interference, general affective distress, and daily activity. Additional analyses showed that change in pain-related anxiety remained a significant predictor of each outcome independent of change in depression. Decreased depression did not predict improvement in interference or daily activity after pain-related anxiety was controlled (McCracken & Gross, 1998).

In their study of helplessness, Burns et al. (1998) compared change in this psychological variable with change in physical capacity variables. We did not include any measure of physical capacity in our earlier study of pain-related anxiety. Therefore, we do not know if the relationship between change in pain-related anxiety and treatment outcome is dependent on or independent of changes in physical capacity. Results from Burns et al. (1998) showing a significant interrelation between psychological and physical capacity process variables and results showing significant correlations between pain-related anxiety and physical capacity variables (Burns, Mullen, Higdon, Wei, & Lansky, 2000) suggest the need to clarify the roles of these variables in treatment process.

The purpose of this study is to further examine the role of pain-related anxiety in treatment outcome for chronic pain. Specifically, we analyse whether the role of pain-related anxiety is independent of change in measured physical capacity. We hypothesized that: (a) increased physical capacity and decreased pain-related anxiety would both predict improvement in pain severity, interference, affective distress, activity level, and depression at post-treatment; and (b) change in pain-related anxiety would account for a significant and unique increment in the variance in all outcomes, independent of change in physical capacity. This study employs data from two assessment methods, self-reports and direct measurement of performance. In addition to showing the relative roles of assessed variables, results will show the relative utility of these methods for tracking treatment progress and guiding treatment development.