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PART THREE  EVALUATION OF THE PAIN PATIENT

who do not have evidence of nervous system sensitization or psychological or social processes that might interfere with their recovery. We are skeptical of the value of discography in neck pain patients. CONCLUSION The previous discussion addresses the medical evaluation of chronic pain within the context of patients with cervical spi- nal pain. We have gone into some detail in order to make the point that medical decision making in relation to cervical spine pain is far from simple. It is our opinion that in order for pain patients to participate fully in evaluations of nonmedical fac- tors contributing to their pain, they need to be confident that their problem has been evaluated thoroughly from a medical perspective. Thus, it is important for physicians participating in a multidisciplinary team either to have a lot of expertise in medical aspects of the problems that afflict their patients or to consult with colleagues who have this expertise. During the past 35 years, CNSS has emerged as an import- ant phenomenon in chronic pain. 58,59 Early research on nonhu- mans demonstrated that they predictably developed CNSS in response to tissue injury and that the CNSS was manifested by characteristic changes in the behavior of dorsal horn neurons in the spinal cord, including a lowered response threshold and an expansion of receptive fields. 59 Expansion of receptive fields was postulated to correlate with referral of pain and lowered response threshold with hyperalgesia. 60,61 Several methods have been developed to assess CNSS in humans. Among them is quantitative sensory testing, which has shown that people with chronic pain demonstrate reduced thresholds to multiple modalities of sensory stimulation, in- cluding pressure, thermal, and electrical stimuli. 62,63 These abnormalities occur when stimuli are applied to the specific location of the reported pain and even to body regions where patients do not experience clinical pain. Another approach has been to study withdrawal reflexes in response to potentially noxious stimuli. Relevant studies have shown that these reflexes can be elicited among chronic pain patients at lower stimulus intensities than the ones required to elicit the reflexes in healthy people. 64,65 Still another promising method for assessing CNSS is func- tional MRI (fMRI). Several investigators have used fMRI methodology to identify brain areas associated with processing of noxious stimuli and have found that patients with chronic pain (e.g., FM, chronic low back pain, and chronic pelvic pain) demonstrate more dramatic activation of these areas than healthy controls. 66,67 Findings from the aforementioned lines of inquiry have been interpreted by several researchers as evidence of CNSS among people with persistent pain 60 and as a central feature in the development of neuropathic pain. 68 Although these proposals have not been conclusively proven, the widespread belief among many neuroscientists and pain specialists that CNSS is a major factor in chronic pain has implications for the evaluation of the condition. At a conceptual level, CNSS challenges the simple di- chotomy between organic pain and psychogenic pain that held sway in the orthopedic literature of a generation ago. 47 At the level of clinical evaluation of an individual patient, the absence of definitive tests to determine the presence of CNSS makes it difficult for a clinician to rule in or out the hypothesis that it is affecting symptoms. The ambiguity introduced by CNSS is increased by the fact that although it is usually identified during an examination by a physician, it is not a medical diagnosis in Assessment of Central Nervous System Sensitization

the usual sense. For example, the International Classification of Disease , 10th edition, does not include any codes that can be used to designate that a patient’s pain is a reflection of CNSS. Also, no clear delineation has been drawn between CNSS versus psychological factors as a cause of persistent symptoms. The evaluation of CNSS is given a separate section in this chapter because of its ambiguous middle ground status between tradi- tional medical processes and psychological processes. At a practical level, clinicians who treat chronic pain pa- tients need to be aware that CNSS may be playing a role in the reports of their patients. One reason for this is that in the pres- ence of CNSS, many of the inferential rules followed by clini- cians when they interpret reports of pain are invalid because the rules are based on a simple model of an isomorphic correspon- dence between symptoms and dysfunction of tissues (nerves, joints, periarticular tissues, muscles) in the region where the patient indicates pain. The inferential rules are simply not valid when CNSS has occurred. For example, stocking glove numb- ness has long been considered a nonphysiologic complaint, but it can logically be interpreted as a result of CNSS. 69 Another practical issue is that clinicians should not expect to find a one- to-one relation between symptoms and a definable structural lesion in a patient whose pain is mediated by CNSS rather than by ongoing nociceptive input from specific body locations. Fi- nally, clinicians need to be cautious about invasive therapies for patients whose pain is mediated by CNSS. The problem is that the pain of such patients may be generated primarily by spontaneous activity within the nervous system rather than by ongoing nociception from peripheral tissues, so that surgical alterations of tissues have little impact on it. Given the potential importance of CNSS in the symptoms and functional limitations of pain patients, it would be highly desirable to have sensitive and specific tests to determine whether it is occurring in individual patients. Unfortunately, although the methods described earlier and several others have been examined in research on CNSS, 63,67 no definitive test for its presence is available for clinical use. In clinical set- tings, practitioners usually rely on various indirect indices to decide whether CNSS is playing a major role in their patients’ symptoms. 70 Assessment of Psychosocial Factors A comprehensive psychological evaluation of a pain patient is a fundamental component of a multidisciplinary evaluation. It addresses the specific psychosocial, behavioral, cognitive, and contextual factors such as current mood (anxiety, depression, anger), interpretation of the symptoms, expectations about the meaning of symptoms, and the responses to the patient’s symp- toms by significant others (e.g., family members, coworkers), each of which contributes to the subjective experience of pain. This type of information should be included in the develop- ment of a comprehensive treatment plan. PSYCHOLOGICAL FACTORS AS CAUSES VERSUS CONSEQUENCES OF CHRONIC PAIN Psychological Factors as Causal Agents in Development of Chronic Pain Patients often resist psychological evaluations because they in- tuitively sense that the outcome of such evaluations might be the conclusion that their pain is a result of psychological dysfunction rather than the injury to which they attribute their symptoms. Indeed, early reports suggested that preexisting psychopathol- ogy or neurotic traits might be the underlying mechanisms for unremitting chronic pain. 71,72 As early as 1953, Gay and Abbot 71 mentioned “neurotic reactions,” noting that particular psycho- logical factors predisposed an individual to chronic problems after an injury. In 1982, Blumer and Heilbronn 72 postulated that