Chapter 12. Psychological Aspects of Pain

It is important to consider how we conceptualize pain. Our views of pain will influence our evaluations of patients who report pain and the nature of the interventions that we use to treat them. The way in which we conceptualize pain depends largely on the nature of the information acquired and the models we were exposed to during our training. In the first section of this chapter, we review the traditional conceptualizations of pain. Although these models are not necessarily inaccurate, they are incomplete. We propose that a broader, multidimensional perspective is required to understand pain and to treat patients appropriately. We describe the role of behavioral, cognitive, and affective factors that have been shown to be relevant to the experience of pain, disability, and response to treatment. We provide data demonstrating that these psychological factors may have an effect on both patients’ behavior and physiology. Finally, we raise the issue of the “patient uniformity myth” and describe the subgroups of pain patients based on psychosocial and behavioral characteristics. We provide preliminary data suggesting that knowledge of such patient subgroups may serve as a basis for matching patients to treatments based on their characteristics.

[Preparation of this manuscript was supported by grants from the National Institute of Child Health and Development (P01 HD33989) and the National Institute of Arthritis and Musculoskeletal and Skin Diseases (R01 AR 44724) awarded to the first author and the National Institutes of Health/Shannon Director’s Award (R55 AR44230) awarded to the second author.]

Historically, pain has been understood from the perspective of Cartesian dualism wherein pain was viewed as purely sensory, reflecting the degrees of incoming noxious sensory stimuli. This perspective assumes that there are two ends to a pain pathway. At the periphery are sensory receptors where noxious information is received; at the other end, regions located in the brain where information is registered passively. From this perspective, noxious stimulation inevitably results in the sensation of pain, as if pulling a string at the periphery activates a bell located in the brain. Variations of this model have been prominent since first proposed by Aristotle.

A central belief of sensory models is that the amount of pain experienced is a direct result of the amount, degree, or nature of sensory input or physical damage and is explained in terms of specific physiologic mechanisms. Clinically, it is expected that the report of pain will be directly proportional to the amount of pathology. This model dictates that assessment should focus on identifying the cause of the pain. Once identified, treatment should involve removal of the cause or severing the specific pain pathways by surgical or pharmacologic means.

Sensory models continued to maintain a prominent position in medicine despite the inability of this model to account for a number of observations. For example:

• Patients with equivalent degrees and types of objectively determined tissue pathology vary widely in their reports of pain severity.
• Patients with only minimal objectively determined pathology may report severe pain.
• Asymptomatic individuals often reveal significant amount of physical pathology on imaging procedures that might be expected to produce pain.
• Surgical procedures designed to inhibit pain transmission by severing neurologic pathways believed to be underlying the reported pain may fail to alleviate pain.
• Patients with equivalent degrees of tissue pathology who are treated with identical treatments respond in widely differently ways.
• There are only modest associations among impairment, pain, and disability.

Thus, we see a number of paradoxes in clinical practice: patients who report severe pain with limited physical pathology and, conversely, individuals who have significant physical pathology but no pain; pain pathway ablated but continued pain; and identical treatments provided for the same diagnosis with different outcomes.

Unfortunately, for many chronic pain sufferers, the underlying causes for their pain frequently remain unknown despite the development and use of sophisticated diagnostic imaging procedures such as computed tomography (CT) scan or magnetic resonance imaging (MRI). For example, objective evidence of physical pathology is only identified in about 15% of the cases of back pain.1 In some conditions, such as recurrent headaches, diagnostic procedures do not reveal any biologic problem that is sufficient to account for the pain reported. Obviously, something other than identifiable physical pathology is influencing patients’ reports.

How can such paradoxes be understood? As is frequently the case in medicine, when objective physical evidence and explanations prove inadequate to explain symptoms, psychological alternatives are proposed. If the pain reported by a patient is believed to be disproportionate to objectively determined physical pathology or if the complaint is recalcitrant to so-called appropriate treatment, then it is assumed that psychological factors must be involved, even if not causal. Thus, there appears to be a somatogenic-psychogenic dichotomy in how pain is construed.

It is important to realize that determination of whether the reported pain is disproportionate is subjective. There is no objective way to determine how much pain is proportionate. How much should a given amount of tissue pathology hurt? Similarly, determination of appropriate treatment is not totally objective. Different health care providers might recommend widely different treatments for patients with the same presenting symptoms. For example, treatments for patients with temporomandibular disorders range from surgery to psychotherapy.

The somatogenic-psychogenic dichotomy forms the basis for the distinction underlying attempts to identify “functional” versus “organic” pain, as well as references to a “functional overlay.” The American Psychiatric Association2 created two psychiatric diagnoses associated with pain in the 4th edition of the Diagnostic and Statistical Manual of Mental Disorders—pain associated with psychological factors either with or without a diagnosed medical condition. The specific diagnosis of “Pain Disorder Associated with Psychological Factors and a General Medical Condition” is characterized by the fact that both psychological and a general medical conditions have important roles in the onset, severity, exacerbation, and maintenance of pain. This set of diagnoses is so broadly defined, however, that virtually all patients who have persistent pain could be diagnosed as suffering from a psychiatric disorder.

A variation of the dichotomous somatic-psychogenic views is a conceptualization that is ascribed to by many insurance carriers and other third-party payers. They suggest that if physical pathology is insufficient to support the claim of pain, then the complaint is invalid. Instead, pain is assumed to result from symptom exaggeration or outright malingering. The assumption is that reports of pain without adequate biomedical evidence are motivated primarily by desire for financial gain. This belief has resulted in a number of attempts to catch malingerers using surreptitious observation methods and the use of sophisticated biomechanical machines geared toward identifying inconsistencies in functional performance. There is, however, very little empirical support for this belief. No studies, for example, have demonstrated dramatic improvement in pain reports subsequent to receiving disability awards (i.e., no further need to exaggerate symptoms).

The conceptualizations previously described view physical and psychological factors as if they are mutually exclusive. Next, we examine the nature of the psychological processes and factors that have been demonstrated to play an important role in pain perception, disability, and response to treatment.

A number of psychological principles based in leaning theory have been extended to pain. These principles provide helpful explanations for many clinical observations. Moreover, a number of cognitive and affective factors have been demonstrated to influence expressions of pain and participation in rehabilitation. We can consider the major psychological, sociocultural, and behavioral principles and factors studied and then consider how they can be integrated to create a comprehensive model of pain that can serve as a guide for assessment and, ultimately, treatment.

Operant Learning Mechanisms

As long ago as the early part of the twentieth century, the effects of environmental factors in shaping the experience of pain were acknowledged. A new era in thinking about pain began in 1976 when Fordyce3 extended the principles of operant conditioning to chronic pain and disability.

In the operant conditioning formulation, behavioral manifestations of pain rather than pain per se are central. When a person experiences noxious sensation, the initial response is a withdrawal or escape response. This may be accomplished by avoidance of activity believed to cause or exacerbate pain, help-seeking to reduce symptoms, and so forth. These behaviors are observable and, consequently, subject to the principles of operant conditioning, namely, reinforcement and avoidance learning.

The operant view proposes that pain behaviors, such as avoidance of activity to protect a wounded limb from producing additional noxious input, may come under the control of external contingencies of reinforcement (responses increase or decrease as a function of their reinforcing consequences). It is these reinforcement contingencies that contribute to the maintenance of the problems associated with chronic pain and disability. Pain behaviors (e.g., limping, grimacing, and inactivity) are conceptualized as overt expressions of pain, distress, and suffering. These behaviors may be positively reinforced directly, for example, by attention from a spouse or from health care providers. Pain behaviors also may be maintained by the escape from noxious stimulation through the use of drugs or rest, or the avoidance of undesirable activities such as work. In addition “well behaviors” (e.g., activity, working) may not be positively reinforcing, and the more rewarding pain behaviors may, therefore, be maintained.

We can illustrate the role of operant factors in a case of chronic back pain. When a woman with a painful back has a flare-up, she may lie down on the floor and hold her back. Her husband will notice these behaviors and infer that she is in pain. The husband’s behavioral response is influenced by his observation of her behavior. He typically responds to her pain complaints by spending extra time and massaging her back. In this case, her lying down has resulted in the pain sufferer receiving attention from her husband, a positive consequence. According to the laws of operant learning, behaviors that result in a positive consequence are more likely to recur.

Another powerful way the husband reinforces his wife’s pain behaviors is by permitting her to avoid undesirable activities. When observing his wife lying on the floor, the husband suggests that they cancel their plans to get together with his brother that evening. If the pain sufferer would prefer not to spend time with her husband’s brother, then the avoidance of the undesirable activity is reinforced and may contribute to reports of pain whenever activities with her husband’s brother are planned. In this situation, her pain reports and behaviors are rewarded both by her husband providing her with extra attention and support, and by the opportunity to avoid an undesirable social obligation.

It is important to clarify that the operant learning does not require the pain sufferer’s intentional and conscious efforts to elicit a desirable outcome. It results from a gradual learning process that neither the sufferer nor others recognize. One should not assume pain behaviors are synonymous with malingering. Malingering involves the patient consciously and purposely faking a symptom such as pain for some gain, usually financial. In the case of pain behaviors, there is no suggestion of conscious deception; rather, the unintended performance of pain behaviors results from laws of learning based on environmental reinforcement contingencies. Typically, there is little awareness that these behaviors are being displayed or that the patient is consciously motivated to obtain a positive reinforcement from the behaviors. The pain behavior in response to initial injury may encounter reinforcing events, thereby determining probability of that behavior recurring in the future. Once the behavior is learned, the presence of initial pain is no longer needed for that behavior to recur.

The operant conditioning formulation does not concern itself with the initial cause of pain. Rather, it considers pain an internal subjective experience that can only be indirectly assessed and may be maintained even after an initial physical basis of pain has resolved. Because of the consequences of specific behavioral responses, it is proposed that pain behaviors may persist long after the initial cause of the pain is resolved or greatly reduced. Thus, in one sense, the operant conditioning model can be viewed as analogous to the psychogenic models described earlier. That is, psychological factors are treated as secondary, reactions to sensory stimulation, rather than directly involved in the perception of pain per se.

The operant view has generated what has proven to be an effective treatment for select samples of patients with chronic pain.4 Treatment focuses on eliminating pain behaviors by withdrawal of attention and increasing “well behaviors” (e.g., activity) by positive reinforcement. Although operant factors undoubtedly play a role in the maintenance of disability, exclusive reliance on the operant conditioning model to explain the experience of pain may not be appropriate. It has been criticized for its exclusive focus on motor pain behaviors, failure to consider the emotional and cognitive aspects of pain, and failure to treat the subjective experience of pain.5

Respondent Learning Mechanisms

Factors contributing to chronicity that have previously been conceptualized in terms of operant learning may also be initiated and maintained by classical or so-called respondent conditioning.6,7 If an aversive stimulus is paired with a neutral stimulus several times, the neutral stimulus will come to elicit aversive experience in the individual. The patient leans to anticipate negative consequences even in the absence of the noxious stimulus. This process has been observed frequently in cancer patients receiving chemotherapy. Patients have been observed to report nausea, even before any cytotoxic medication has been administered, when they enter the room where they have received chemotherapy. Similarly, a patient with back pain who received a painful treatment from a physical therapist may become conditioned to experience a negative emotional response to the presence of the physical therapist, to the treatment room, and to any stimulus associated with the nociceptive stimulus (e.g., exercise equipment). The negative emotional reaction may lead to tensing of muscles and this, in turn, may exacerbate pain, thereby reinforcing the association between the presence of the physical therapist and pain.

The most relevant emotional conditioning in pain probably is anxiety. Anxiety is often the affect underlying avoidance of activities. Pain patients often experience temporary aggravation of pain following physical activities. Avoiding such activities leads to no pain exacerbation, thus reinforcing inactivity and maintaining anxiety for activity. In other words, the persistence of avoidance of specific activities reduces disconfirmations that could provide corrective feedback.8 Insofar as avoidance does not produce disconfirmation, the behaviors will persist.9 By contrast, when the anticipated consequence does not occur (disconfirmation), modification of learning also takes place. Thus, the physical therapist may have to encourage the patient to exercise to provide disconfirmation of the anticipation that exercise will hurt and lead to increased injury. The therapist has to emphasize that hurt and harm are not the same things. Both respondent conditioning and operant learning may contribute to the development and maintenance of dysfunctional behavioral patterns in patients with chronic pain. Over time, more and more activities, people, and physical locations may be seen as eliciting or exacerbating pain and will be avoided (stimulus generalization). Fear of pain and avoidance may become conditioned to an expanding number of situations (response generalization). In addition to the avoidance learning, pain may be exacerbated and maintained in these encounters with potentially pain-increasing situations because of the anxiety-related increases in sympathetic activation and muscle tension that may occur in anticipation of pain and, also, as a consequence of pain. Thus, as we emphasize later in this chapter, psychological factors may directly affect nociceptive stimulation and need not be viewed as only reactions to pain.

Social Learning Mechanisms

Social learning has received some attention in the study of acute pain and the development and maintenance of chronic pain states. From this perspective, how we experience pain is shaped and influenced by what we have observed, so-called observational learning. That is, individuals can acquire responses that were not previously in their behavioral repertoire by watching others perform these activities. Children acquire attitudes about health, health care, and the perceptive style for recognizing and understanding bodily symptoms from their parents and social environment. They also learn how injuries and diseases should be attended. As they grow older, the learning emerges as their tendency to ignore or over-respond to symptoms they experience. The culturally acquired interpretations of symptoms determine how people deal with illness.

There is ample experimental evidence of the role of social learning from controlled laboratory pain studies and some evidence based on observations of patients’ behaviors in field and clinical settings. Physiologic responses to pain stimuli may be conditioned during observation of others in pain. For example, patients on a burn unit have sufficient opportunity to observe the responses of other burn patients.10 Each patient’s response to his or her situation is affected by observations of other patients. In one study, children of chronic pain patients chose more pain-related responses to scenarios presented to them than did children of healthy or diabetic parents. Moreover, teachers rated the children of pain patients as displaying more illness behaviors (e.g., complaining, absences from school, visits to the school nurse) than the children of healthy controls.11 Expectancies as well as actual behavioral responses to noxious stimuli are based, at least partially, on prior social leaning history. This situation may contribute to the marked variability in response to objectively similar degrees of physical pathology noted by health care providers.

A great deal of research has been directed toward explicating the role of cognitive factors in pain. These studies have consistently demonstrated that patients’ attitudes, beliefs, and expectancies about their situation, themselves, their coping resources, and the health care system affect the reports of pain, activity, disability, and response to treatment.12,13

Beliefs About Pain

Clinicians working with patients who have chronic pain are aware that patients having similar pain histories and expressions of pain may differ greatly in their beliefs about their pain.14 Behavior and emotion are influenced by how one interprets events, rather than by objective characteristics of the events. Thus, pain, when interpreted as signifying ongoing tissue damage or a progressive disease, is likely to elicit considerably more suffering and behavioral dysfunction than when it is viewed as being the result of a transient problem that eventually will improve. Consider the case of an individual who wakes up one morning with a headache. Very different responses would be expected if he attributed the headache to excessive alcohol consumption the night before than would be the case if he interpreted the headache as a signal of a brain tumor. Thus, although the amount of nociceptive input in the two cases may be equivalent, the emotional and behavioral responses would vary in nature and intensity.

Certain beliefs may lead to maladaptive coping, increased suffering, and greater disability. Patients who believe that there is nothing they can do to control pain may be passive in their coping efforts and fail to make use of available resources to cope with pain. Patients who consider their pain to be an unexplainable mystery feel helpless and clueless as to how to cope with the situation. The sense of helplessness contributes to negative evaluations of one’s own abilities and coping strategies as effective in controlling and decreasing pain.15 Once beliefs and expectancies about a disease are formed, they become stable and are very difficult to modify. Patients tend to avoid experiences that could invalidate their beliefs (disconfirmation), and they guide their behavior in accordance with these beliefs (confirmation), even when the beliefs are no longer valid. Consequently, as noted earlier when the role of respondent conditioning was described, they do not obtain corrective feedback. For example, feeling muscular pain following activity may be caused by lack of muscle strength and general deconditioning and not by additional tissue damage.

Patients with chronic low back pain generally demonstrate poor behavioral persistence in various exercise tasks, and their performance on these tasks is independent of physical exertion or actual self-reports of pain, but rather is related to previous pain reports.16 These patients appear to have a negative view of their abilities and expect increased pain if they perform physical exercises. Thus, the rationale for their avoidance of exercise is not the presence of pain but their learned expectation of heightened pain and accompanying physical arousal that might exacerbate pain and reinforce their beliefs regarding the pervasiveness of their disability. If patients view disability as an expected consequence of their pain, that activity is dangerous, and the pain is an acceptable excuse for neglecting responsibilities, they are likely to experience prolonged disability. Patients’ negative perceptions of their capabilities for physical performance form a vicious circle, with the failure to perform activities reinforcing the perception of helplessness and incapacity. Once again, avoidance of activity prevents disconfirmation.

The strong influence by one’s belief system can also be associated with pain resulting from serious diseases. Spiegel and Bloom17 reported that the pain severity of cancer patients could be predicted by the use of analgesics, affective state, and assumed pathology of pain. Patients who attributed their pain to a progression of their underlying disease experienced more pain despite comparable levels of disease than did patients with more benign interpretations.

In addition to beliefs about capabilities to function despite pain, beliefs about pain per se appear to be of importance in understanding response to treatment, adherence to self-management activities, and disability.15 When successful rehabilitation occurs, there appears to be an important cognitive shift from beliefs about helplessness and passivity to resourcefulness and ability to function regardless of pain.12,13

Clearly, it is essential for patients with chronic and recurrent pain to develop adaptive beliefs and to emphasize the importance of maintaining functionality despite pain. In fact, changes in pain levels do not necessarily parallel changes in other variables of interest, including activity level, medication use, return to work, rated ability to cope with pain, and pursuit of further treatment.18

Self-Efficacy

Another important cognitive factor related to beliefs about pain is the belief about one’s ability to cope with pain, referred to as self-efficacy.19 A self-efficacy expectation is defined as a personal conviction that one can successfully execute a course of action (perform required behaviors) to produce a desired outcome in a given situation. This variable has been demonstrated as a major mediator of therapeutic change. Given sufficient motivation to engage in a behavior, it is a person’s self-efficacy beliefs that determine the choice of activities he or she will initiate, the amount of effort that will be expended, and how long the person will persist in the face of obstacles and aversive experiences. Efficacy judgments are based on four sources of information regarding one’s capabilities, listed in descending order of impact:

• One’s own past performance at the task or similar tasks
• The performance accomplishments of others who are perceived to be similar to oneself
• Verbal persuasion by others that one is capable
• Perception of one’s own state of physiologic arousal, which is in turn partly determined by prior efficacy estimation19

Experience of performance mastery is critical in developing adequate self-efficacy belief. It can be achieved by starting patients at a modest level with graded activities added gradually. From this perspective, the occurrence of coping behaviors is conceptualized as being mediated by people’s beliefs that situation demands do not exceed their coping resources. Council and colleagues20 asked patients to rate their self-efficacy as well as expected level of pain related to performing movement tasks. Patients’ performance levels were highly related to their self-efficacy expectations, which, in turn, appeared to be determined by their expectancy of pain levels.

Catastrophizing

So-called catastrophizing—extremely negative thoughts about one’s plight and interpretation of even minor problems as major catastrophes—appears to be a particularly potent way of thinking that greatly influences pain and disability. Several lines of research, including experimental laboratory studies of acute pain with normal volunteers and field studies with clinical patients suffering clinical pain, have indicated that catastrophizing and adaptive coping strategies are important in determining reactions to pain.21 Individuals who spontaneously use catastrophizing self-statements reported more pain than those who did not catastrophize in several acute and chronic pain studies. Turk and colleagues concluded that “what appears to distinguish low from high pain tolerant individuals is their cognitive processing, catastrophizing thoughts and feelings that precede, accompany, and follow aversive stimulation” (p. 197).22

Coping

Self-regulation of pain management depends on the individual’s specific ways of dealing with pain, adjusting to pain, and reducing or minimizing pain and distressed caused by pain—coping strategies. Coping is manifested spontaneously; coping action is employed purposefully and intentionally, and it can be assessed in terms of overt and covert behaviors.13 Overt behavioral coping strategies include rest, medication, and use of relaxation. Covert coping strategies include various means of distracting oneself from pain, reassuring oneself that the pain will diminish, seeking information, and problem solving. Coping strategies are thought to alter both the perceived pain intensity and one’s ability to manage or tolerate pain and to continue everyday activities.

Coping can be beneficial or detrimental in management of pain. Studies have found active coping strategies (e.g., efforts to function in spite of pain or to distract oneself from pain, such as engaging in activity, ignoring pain) to be associated with adaptive functioning. Passive coping strategies (e.g., depending on others for help in pain control and restriction on activities) were related to greater pain and depression.21 In a number of studies, it has been demonstrated that if participants are instructed in the use of adaptive coping strategies, the pain intensity decreases and tolerance of pain increases.14 The most prominent factor in poor coping appears to be the presence of catastrophizing rather than differences in the nature of specific strategies.

Cognitive factors may act indirectly on pain and disability by reducing physical activity, and, consequently reducing muscle flexibility, strength, and tone. Fear of re-injury, fear of losing disability compensation, and low level of job dissatisfaction can also adversely influence return to work.

Pain sufferers can develop ways of coping that in the short run seem adaptive but in the long run serve to maintain the chronic pain condition and result in greater disability. As noted earlier, one of these ways of coping is avoidance of activities because of the fear of pain or injury. For example, following an accident in which a man hurts his back, he learns that certain movements make his pain worse. In response, he may stop engaging in activities that exacerbate his pain and restrict his movements in an attempt to avoid pain. As a result, he may lose muscle strength, flexibility, and endurance. Here a vicious circle can begin, for as the muscles became weaker, more and more activities caused pain. As individuals with back pain remain inactive and become more physically deconditioned, they may not allow themselves the opportunity to be rehabilitated by identifying the activities that build flexibility, endurance, and strength without the risk of pain or injury. In addition, the distorted movements and postures that individuals use to protect themselves from pain may cause further pain unrelated to the initial injury. For example, when a woman who has hurt her leg limps, she protects muscles on one side of her back but the muscles on the other side of her back may become overactive and can develop into painful conditions of their own. Thus, avoidance of activity, although it is a seemingly rationale way to manage a pain problem, can actually play a large role in maintaining the chronic pain condition and increasing disability. In addition to contributing to the maintenance of the pain condition, the use of avoidant-coping strategies has other negative consequences.

After having limited success in controlling pain, the chronic pain sufferers may perceive pain and the factors that influence the pain to be outside of their personal control. Individuals who feel pain is uncontrollable are not likely to attempt new strategies to manage their pain. Instead, pain sufferers feel increasingly frustrated and demoralized when uncontrollable pain interferes with participation in rewarding recreational, occupational, and social activities. It is common for pain sufferers to resort to passive coping strategies, such as inactivity, self-medication, or alcohol, to reduce emotional distress and pain.

Pain sufferers who feel little personal control over their pain are also likely to catastrophize about the impact of situations that trigger or exacerbate their pain and about pain flare-ups. In contrast, individuals who believe in their own ability to control the situations contributing to flare-ups are more resourceful and are more likely to develop self-management strategies that are effective in limiting the impact of the pain episodes or flare-ups, and thus are able to limit the impact of the pain problem.

Whereas maladaptive cognition can worsen pain, adaptive cognition can have a positive effect. Individuals who feel they have a number of successful methods for coping with pain may suffer less then those who feel helpless and hopeless. Psychological interventions such as relaxation, contingency management, and coping skills training have been shown to be effective in helping people with persistent pain to either eliminate their pain or, if pain cannot be eliminated, reduce their pain, distress, and suffering. These interventions are designed not only to decrease pain, but also to improve physical and psychological functioning.

Several studies have suggested that psychological factors may actually have a direct effect on physiologic parameters associated more directly with the production or exacerbation of nociception.23 Cognitive interpretations and relevant arousal may have a direct effect on physiology by increasing sympathetic tones, endogenous opioid (endorphins) production, and levels of muscle tension.

Effects of Thoughts on Autonomic Arousal

Circumstances that are appraised as potentially threatening to safety or comfort are likely to generate strong physiologic reactions. In a sample of patients suffering from recurrent migraine headaches, Jamner and Tursky24 observed an increase in skin conductance, indicating autonomic arousal, in response to seeing words describing migraine headaches simply displayed on a screen. Prolonged autonomic arousal might contribute to headaches.

Chronic increases in sympathetic nervous system activation are known to decrease skeletal muscle tone and, thus, may set the stage for hyperactive muscle contraction and possibly for the persistence of a contraction following conscious muscle activation. Excessive sympathetic arousal is viewed as the immediate precursor of muscle hypertonicity, hyperactivity, and persistence. These responses, in turn, are the proximate causes of muscle spasm and pain. In is not usual for someone in pain to amplify the significance of the problem and needlessly turn on the sympathetic nervous system. In this way, thought processes may influence sympathetic arousal and predispose the individual to further pain or otherwise complicate the process of recovery.

The direct effect of thoughts on muscle tension response was demonstrated by Flor and colleagues.23 These investigators interviewed patients with back pain disorders, patients with other pain disorders, and healthy individuals. Muscle tension sensors were placed on the surface of the lower back, forearm, and forehead. During the monitoring of muscle activity, patients were asked to recall and describe in as much detail as possible the last time they experienced extreme pain and the last time they experienced severe stress. The study found that when discussing their pain or stress, the patients with back pain had significantly elevated muscle tension in their back, but not in their forehead or forearm. However, when these patients with back pain were resting and not discussing their pain or stress, their back muscle tension level was no higher than the non–back pain patients or the healthy individuals. Neither the non–back pain patients nor the healthy individuals showed elevations in muscle tension when discussing severe stresses. Thus, patients with back pain showed pain site–specific muscular arousal simply by talking about their pain and stress. Similar results have been observed in studies with patients who had chronic arm and shoulder pain25 and those with temporomandibular disorders.26

Effects of Thoughts on Biochemistry

Bandura and colleagues27 directly examined the role of central opioid activity in cognitive control of pain. They trained subjects to use various coping strategies for alleviating pain, including attention diversion from pain sensations to other matters, engaging imagery, imaginal separation (dissociation) of the limb in pain from the rest of the body, transformation of pain as nonpain sensations, and self-encouragement of coping efforts. They demonstrated that (1) self-efficacy increased with cognitive training, (2) self-efficacy predicted pain tolerance, and, importantly, (3) naloxone (an opioid antagonist) blocked the effects cognitive coping. The latter result specifically implicates the direct effects of thoughts on endogenous opioids. Bandura and colleagues concluded that the physical mechanism by which self-efficacy influences pain perception might at least be partially mediated by the endogenous opioid system.

O’Leary and colleagues28 provided stress management treatment to patients with rheumatoid arthritis. Degree of self-efficacy (expectations about the ability to control pain and disability) enhancement was correlated with treatment effectiveness. Patients with higher self-efficacy and greater self-efficacy enhancement displayed greater numbers of suppressor T cells. Significant effects were also obtained for self-efficacy, pain, and joint impairment. Increased self-efficacy for functioning was associated with decreased disability and joint impairment.

The International Association for the Study of Pain specifies that “[Pain] is unquestionably a sensation in a part or parts of the body but it is also always unpleasant and therefore also an emotional experience.”29 The affective factors associated with pain include many different emotions, but they are primarily negative in quality. Anxiety and depression have received the greatest amount of attention in patients with chronic pain; however, anger has recently received considerable interest as an important emotion in these patients.

Depression and Anxiety

Research suggests that from 40% to 50% of patients with chronic pain suffer from depression.30 There has been extensive debate concerning the causal relationship between depression and pain. In the majority of cases, depression appears to be patients’ reaction to their plight.31

Given the chronicity and impact, it should not surprise us that a large number of patients with chronic pain are depressed. It is interesting to ponder the other side of the coin. How is it that all such patients are not depressed? Turk and colleagues examined this question and determined that patients’ appraisals of the impact of the pain on their lives and of their ability to exert any control over the pain and their lives mediated the pain-depression relationship.31,32 We have also recently noted that pain severity and sensitivity do not differentiate depressed from nondepressed chronic pain patients.33

Anger

Anger has been widely observed in individuals with chronic pain. Pilowsky and Spence34 reported an incidence of “bottled-up anger” in 53% of patients with chronic pain. Kerns and colleagues35 noted that the internalization of angry feelings was strongly related to measures of pain intensity, perceived interference, and reported frequency of pain behaviors. Anger and hostility are closely associated with pain in persons with spinal cord injuries.36

Frustrations related to persistence of symptoms, limited information on etiology, and repeated treatment failures along with anger toward employers, the insurance carrier, the health care system, family members, and themselves, all contribute to the general dysphoric mood of these patients. The impact of anger and frustration on exacerbation of pain and treatment acceptance has not received adequate attention. It would be reasonable to expect that the presence of anger may serve as an aggravating factor, associated with increasing autonomic arousal and blocking motivation and acceptance of treatments oriented toward rehabilitation and disability management rather than cure, which are often the only treatments available for chronic pain.

The importance of psychological factors has been widely recognized and many pain treatment programs include interventions designed to address cognitive, affective, and behavioral components of the pain experience. One consistent finding seems to be that each treatment seems to work for some patients but no treatment works for everyone. Thus, clinicians must be careful not to be trapped in the “patient homogeneity myth.” Although characterization of patient populations may help classify patients and direct treatment plans, research has shown that any populations that are defined by pain diagnoses demonstrate heterogeneity in their cognitive-affective-behavioral dimensions.

To address the heterogeneity of pain patients, Kerns and colleagues37 developed a comprehensive inventory, the Multidimensional Pain Inventory (MPI). The MPI was designed to assess the cognitive, affective, and behavioral responses of patients with chronic pain to their symptoms. The MPI focuses on patients’ interpretation of their plight, effects of interpersonal relationships, and functional limitations. Using a statistical procedure (i.e., cluster analysis), Turk and colleagues38 identified three distinct profiles of patients with chronic pain. They were labeled as: (1) “dysfunctional” (DYS), characterized by high levels of pain, life interference, emotional distress, and functional limitations; (2) “interpersonally distressed” (ID), similar to the DYS but further characterized by low level of support from their significant others; and (3) “adaptive copers” (AC), characterized by low levels of pain, functional limitations, and emotional distress. The classification system has been replicated in several studies conducted in Finland,39 the Netherlands,40 and in a large, multi-centered study in the United States.41

Research using the MPI has demonstrated that the majority of patients with diverse chronic pain disorders (e.g., low back pain, temporomandibular disorder, headaches, fibromyalgia, and metastatic disease) can be classified into one of the three empirically derived profiles.38,42,43 Although the percentage of patients classified within each of the profiles varies across pain disorders, patients’ styles of adaptation to pain are very consistent within a profile regardless of their medical diagnosis, suggesting the relative independence of psychosocial dimension of chronic pain from biomedical factors (Fig. 12-1). The results from these studies suggest that a dual-diagnostic approach may be useful, whereby two diagnoses are assigned concurrently—physical and psychosocial-behavioral—and treatment plans can be developed within each of the diagnostic frames.44

Example of Treatments Matched to Psychosocial and Behavioral Characteristics

We would hypothesize that providing a treatment plan that specifically addresses psychosocial needs of each profile should show superior outcome to unmatched treatment. A basic cognitive-behavioral approach, including cognitive restructuring and behavioral skill training for pain management, is the most widely practiced method by pain psychologists.45 Our previous trials showed that although, as a group, patients with chronic pain show significant treatment gains from this approach, the three profile groups differentially responded to the treatment.46 Most notably, patients who fit into the interpersonally distressed profile did not show significant improvement.46

Instead of the “one-size-fits-all” method, we need to address the “what-treatment-works-for-whom” question. One example can be seen in Fig. 12-2. Three specific plans may be developed on the basis of the profile characteristics of the MPI classification. In this matrix, dysfunctional patients should benefit most from treatment 1, whereas interpersonally distressed patients should show improvement when they undergo treatment 2, over and beyond the improvement expected from the nonspecific effects of treatment. Treatment 3 can be considered as minimal psychological intervention, because adaptive copers are adjusting reasonably well, this minimal approach may be sufficient for these patients to achieve beneficial effects from the overall therapy. Elimination of inappropriate treatments should save cost as well as time, effort, and frustration for patients and treating clinicians.

Understanding of the role of psychological factors has greatly increased since the first edition of this volume was published. Research efforts have confirmed that pain is a multifactorial phenomenon. In particular, several psychological factors, learning principles, cognitive factors, and affective components have been found to significantly influence how people experience pain, cope with pain, and recover from pain. In this chapter, we described different perspectives on pain and suggested that the unidimensional models (biomedical, psychogenic, motivational, behavioral) are inadequate both to explain chronic pain and as the basis for treatment. We examined the range of psychological factors that play an intricate role in pain perception, disability, and response to treatment. We raised a concern about the patient homogeneity myth and described one effort to subdivide patients based on a set of psychosocial and behavioral factors. Finally, we provided some preliminary evidence demonstrating that patients with different characteristics respond quite differently to the same treatment. Additional studies are needed to confirm these results, and studies are needed to evaluate the potential of a specific treatment-matching strategy.

Although we focused in this chapter on the role of psychological factors in chronic pain, we believe that these same factors may play a role in acute pain states as well. We believe that physical, psychosocial, and behavioral factors are all important in the experience of pain, per se. The relative weight of these factors may vary, however, with physical factors making a larger contribution in acute pain states than chronic pain states and psychological factors making a more significant contribution in chronic pain than acute pain. In each of these instances, however, attention should be given to the range of factors that contribute to the total experience of pain.