Psychological Factors in the Experience of Pain

Impact of Psychological Factors in the Experience of Pain Steven J. Linton, William S. Shaw

This article reviews the role of psychological factors in the development of persistent pain and disability, with a focus on how basic psychological processes have been incorporated into theoretical models that have implications for physical therapy. To this end, the key psychological factors associated with the experience of pain are summarized, and an overview of how they have been integrated into the major models of pain and disability in the scientific literature is presented. Pain has clear emotional and behavioral consequences that influence the development of persistent problems and the outcome of treatment. Yet, these psychological factors are not routinely assessed in physical therapy clinics, nor are they sufficiently utilized to enhance treatment. Based on a review of the scientific evidence, a set of 10 principles that have likely implications for clinical practice is offered. Because psychological processes have an influence on both the experience of pain and the treatment outcome, the integration of psychological principles into physical therapy treatment would seem to have potential to enhance outcomes.

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S.J. Linton, PhD, is Professor of Clinical Psychology, Center for Health and Medical Psychology (CHAMP), School of Law, Psychol- ogy and Social Work, Orebro University, Orebro 701 82, Swe- den. Address all correspondence to Professor Linton at: [email protected]

W.S. Shaw, PhD, is Principal Research Scientist, Center for Dis- ability Research, Liberty Mutual Research Institute for Safety, Hopkinton, Massachusetts.

[Linton SJ, Shaw WS. Impact of psychological factors in the expe- rience of pain. Phys Ther. 2011; 91:700 711.]

2011 American Physical Therapy Association

Psychologically Informed Practice

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The experience of pain isshaped by a host of psycholog-ical factors. Choosing to attend to a noxious stimulus and interpret- ing it as painful are examples of 2 factors involving normal psychologi- cal processes. To be sure, pain is a subjective experience, and although it is certainly related to physiological processes, how individuals react to a new episode of pain is shaped and influenced by previous experience. Indeed, without learning from expe- rience, it would be difficult to cope with pain and maintain good health. Thus, these psychological processes have tremendous value for survival.1

Yet, psychological factors are not completely understood, and the translation of their use to the clinic remains a challenge. Therefore, in this article, we focus on the most important psychological factors that have been incorporated into theoret- ical models of pain that may explain pain perception and treatment ben- efits. In our view, awareness of these factors is crucial for understanding patients in pain and is a prerequisite for integrating them into clinical practice.

Applying psychological knowledge in the clinical practice of physical therapy, however, has been quite a challenge. A majority of physical therapists are aware of the impor- tance of psychological factors and attempt to utilize this awareness in their practice.2,3 The application of psychological knowledge in physical therapy might range from providing reassurance to setting goals or inquir- ing about the functional conse- quences of pain. However, there is an apparent lack of knowledge and tools to adequately apply this knowl- edge. For example, although 63% of physical therapists in a primary care setting were aware of the impor- tance of psychological factors, only 47% reported knowledge of utilizing them clinically.3 Furthermore, when asked to specify which psychologi-

cal factors are of importance, most therapists listed some evidence- based factors but also a host of non evidence-based factors.2 Indeed, many of the factors listed by clini- cians were difficult for them to address (eg, economic, drug abuse, or marital issues) in the clinic and did not match the evidence-based fac- tors included in that article.2 Thus, a key to the problem appears to be a lack of clear guidelines for applying the knowledge. We acknowledge that there is currently a lack of clear information as to how psychological factors should be utilized by physical therapists and other clinicians.

One area that is particularly relevant is how early physical therapy treat- ments might prevent the develop- ment of chronic musculoskeletal pain. Although many acute low back pain (LBP) problems resolve, a minority of people (10%) directly develop a persistent problem that disables them for a long period of time.4,5 The transition from acute to chronic pain problems is known to be catalyzed by psychological processes (see article by Nicholas et al6 in this issue). As a review of psychological interventions designed to prevent chronicity has shown positive effects when the psycho- logical techniques are appropriately administered,6 competent applica- tion appears to be vital. In our view, an understanding of the basic psy- chological processes is, therefore, an essential base for competent applica- tion of psychological principles in the clinic.

To date, there has been broad recog- nition of the importance of a biopsy- chosocial view of pain, but a lack of clarity in how the psychological fac- tors actually fit in, not least in clinical situations. How might psychology be utilized to improve care? To this end, we will focus on the central psychological factors and highlight the psychological processes that

affect the pain experience over time. Indeed, we emphasize how psycho- logical factors may contribute not only to the experience of acute pain but also to the development of chronic pain and disability over time. What might be quite a normal and appropriate response in the acute phase paradoxically may be a poor method of coping with persistent pain. Accordingly, we will highlight how psychological factors affect the development of persistent disability and illustrate the processes by describing pertinent theoretical models.

Psychological Processes In this section, we provide an over- view of fundamental psychological processes that are involved in most types of pain problems and high- light how these processes may con- tribute to the development of a per- sistent pain problem. A basic theme is that the psychological processes are highly intertwined and function together as a system. We consider them individually as a means of pre- sentation. Note that these processes also form the basis of the models presented in the next section.

Available With This Article at ptjournal.apta.org

Symposium Podcast: Download an audio or video podcast of the Enhancing Clinical Practice Through Psychosocial Perspectives in the Management of Low Back Pain symposium at CSM 2011 with speakers Julie Fritz, Steven Z. George, Chris J. Main, and William Shaw. The symposium was sponsored by APTAs Orthopaedic Section.

Audio Abstracts Podcast

This article was published ahead of print on March 30, 2011, at ptjournal.apta.org.

Impact of Psychological Factors in the Experience of Pain

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There are different ways in which we might group psychological fac- tors. In our presentation, we attempt to portray the influence of psycho- logical factors, as illustrated in Fig- ure 1, as a sequence of processes, starting with initial awareness of the noxious stimulus, then cognitive processing, appraisal, and interpreta- tion that leads people to act on their pain (ie, their pain behavior).7 These processes are influenced by their consequences and are limited by the environment (eg, cultural and social values). Although we present this as a sequence for understanding, we are aware that this is a model, and much more work is needed to fully describe these processes. In addition to the model, Table 1 provides an overview of the main factors and

their possible consequences for the experience of pain.

Attention An obvious prerequisite for pain per- ception is that our attention is directed toward the noxious stimu- lus. In fact, one function of pain is to demand attention.8 Viewed as a warning signal, pain is helpful because this attention should lead to appropriate responses in dealing with the injury. This view also under- scores why it is difficult to simply ignore pain, particularly if it has alarming characteristics (eg, being very intense, sharp, or unusual).

The dilemma is that we sometimes pay attention to pain when there is little we can do to alleviate it (eg,

having chronic musculoskeletal pain), but do not attend to it when it may be a useful warning signal (eg, during an accident). Although atten- tion is under the control of some basic brain processes, its psycholog- ical function is to motivate behavior. If pain is considered a threat, then the threat value of the (noxious) stimulus helps to steer awareness: the greater the threat, the more attention given. Attention to pain then may be linked to fear and anx- iety and the need to take action (eg, escaping or avoiding it). Vigilance refers to an abnormal focus on pos- sible signals of pain or injury9 that might help explain why a seemingly small injury results in intense pain. This mechanism also underscores the close link between emotional and cognitive processes and atten- tion.7,10 Attentional factors are quite pertinent in the clinic because there are techniques that address them. Distraction techniques teach patients to shift their attention to stimuli other than the pain (eg, by imagining the sounds of waves hit- ting the shore), whereas interceptive exposure shifts attention toward the pain so that the signal will habituate.11

Interpretation Once the noxious stimulus has been attended to, cognitive processes are used to interpret what they mean. This process is highly intertwined with emotional processes, and it sets the stage for behaving.7 How we think about a noxious stimulus is shaped by our previous experiences, which explains why the simple directive think about something else often is impossible to accom- plish. Indeed, the paradox is that attempting to suppress thoughts about pain actually increases the pain experience.12 Cognitive pro- cesses are central in explaining why we sometimes may experience an insignificant stimulus, such as light pressure, as severe pain, or a serious