Towards a comprehensive assessment of chronic pain patients

33.00 + 0.00 C@O5-7967/87

Behw. Res. Ther. Vol. 25, No. 4, pp. 237-249, 1987 F’rintcdin Great Britain

Pcrgamon Journals Ltd

TOWARDS A COMPREHENSIVE ASSESSMENT OF CHRONIC PAIN PATIENTS DENNIS C. TURK’ and THOMAS E. RUDY* ‘Department of Psychiatry and Center for Pain Evaluation and Treatment, *Department of Anesthesiology and Center for Pain Evaluation and Treatment, University of Pittsburgh School of Medicine, 230 Lothrop Street, Pittsburgh, PA 15213, U.S.A.

Summary-The evaluation and treatment of individuals suffering from chronic pain is frequently aligned with how pain is conceptualized. Unidimensional models of pain are reviewed and the inadequacies of conducting assessments from these perspectives are highlighted. Several preliminary attempts at integrating medical and psychoiogical data are discussed. A triarchic, Multiaxial Assessment of Pain (MAP) approach, based on sound taxometric and multivariate classification procedures, is proposed. It is concluded that a comprehensive evaluation of chronic pain patients should include the assessment and integration of physical, psychosocial, and behavioral information.

INTRODUCTION

Advances in the assessment and diagnosis of chronic pain patients have not kept pace with theories of pain and the development of therapeutic modalities. Systematic efforts to evaluate and treat pain patients traditionally have been closely aligned with how pain is conceptualized. Historically, pain has been viewed as either a sensory-physiological event or the result of a psychological process. Consequently, assessment approaches used in the evaluation of chronic pain patients have tended to parallel one of these conceptualizations of pain at the expense of missing relevant information that may have been obtained by the adoption of a more comprehensive perspective. In this article we will (a) briefly review both the sensory and psychological conceptualizations of pain, especially as they relate to assessment; (b) highlight the inadequacies involved in evaluating pain patients from such unidimensional perspectives; (c) review several preliminary attempts to integrate medical and psychological assessment data; and (d) propose a Multiaxial Assessment of Pain (MAP) system that integrates medical, psychosocial, and behavioral findings. Additionally, we will describe how such a MAP system can lead to a more comprehensive evaluation of chronic pain patients, improve clinical decision-making, and advance research effort to evaluate the efficacy of different treatment modalities with diverse groups of patients and different pain syndromes. UNIDIMENSIONAL

The sensory-physiological

CONCEPTUALIZATIONS

view

Traditionally, the biomedical assessment of the chronic pain patient has adhered to the sensory-physiological perspective of pain, whereby pain is viewed as the consequence of biological perturbations. In other words, pain is viewed as sensory phenomena directly linked to the extent of tissue damage or organ pathology. The sensory conceptualization of pain has led to the development and use of assessment procedures designed for two related yet quite distinct purposes. First, because reports of pain are believed to be indicative of tissue damage, medical assessment procedures are conducted in order to establish the nature and extent of the pathology that ‘causes’ the pain. Secondly, in the case of chronic pain, traditional medical assessment methods are used to determine the patient’s degree of physical impairment and disability, both for purposes of rehabilitation and decisions regarding disability compensation. Diagnostic procedures such as X-rays, electromyography, and laboratory tests have been employed for the first purpose and a number of functional evaluation systems have been established for the latter (e.g. American Medical Association, 1971; Brand and Lehmann, 1983). 237

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Interpretation of medical-physical findings have tended to rely on clinical judgments based on the physician’s experience and, occasionally, quasi-standardized criteria (e.g. American Medical Association, 1971; Fairbankl Mbaot, Davies and O’Brien, 1980; Waddell, McCulloch, Kummel and Venner, 1980). Many of these approaches, however, have not been adequately normed, focus on a limited class of pain (e.g. low back pain), or the adequacy of their biometric properties (e.g. reliability, validity, utility) have not been established. Moreover, there remains a good deal of subjectivity both in the manner in which the assessment is conducted and how function is established (possible solutions to this problem are discussed later in this paper). For example, functional assessment of a back pain patient may include items such as ‘straight leg raising’ without specific instructions regarding how this task should be conducted, how the patient’s performance should be scored, or how to maximize motivation. Assessment of pain severity. Attempts to assess the subjective quantity, severity, or intensity of pain per se have also been developed in order to study pain in the laboratory and to evaluate the efficacy of clinical interventions. Perhaps the earliest attempts and still the most frequently used method to measure pain involves the informal use of categorical scales, for example, ‘is your pain mild, moderate, or severe?’ One problem with the use of this type of categorical scale is the frequent application of statistical procedures that assume that the scale consists of equal interval measures. That is, that the difference between mild and moderate is the same as between moderate and severe or that severe is twice as intense as mild. These assumptions are, of course, unwarranted. Another difficulty with this type of scale is that it has a restricted range and thus is not very sensitive to changes that may result from treatment or time. Attempts to resolve the difficulties noted above include the use of visual analog scales that attempt to assess, more precisely, pain severity measurements (e.g. Carlsson, 1983; Reading, 1980). Visual analog scales consist of lines of a specific length, frequently 100 mm with verbal descriptors as anchors (e.g. ‘none’ to ‘worst ever experienced’). Nonetheless, regardless of the technique used to quantify a patient’s level of pain, these assessment methods are based implicitly on the assumption that pain is a unidimensional phenomenon that can be adequately described along a single dimension, namely, intensity. Psychiatric or trait approach

The inability to identify organic pathology for many chronic pain patients and the continued reports of pain following correction of the pathological condition or following the expected period of resolution of an injury, has led to two quite different approaches to conceptualizing chronic pain patients: a psychiatric approach and a behavioral approach. The traditional psychiatric or trait approach to chronic pain suggests that the differences in reports of pain and treatment outcome can be explained by personality characteristics of the patient or the presence of a psychiatric disorder. Attempts to identify subgroups of patients based on personality assessments or the diagnosis of psychopathology have followed from this perspective. Consideration of these findings along with the results of at least some medical assessment procedures frequently are used to classify patients as ‘organic’ or ‘functional’.* In other words, pain patients are treated in a dichotomous fashion, either there is a physical basis for the pain and thus the pain is ‘real’ or, if organic findings are absent or the patient’s pain complaints are ‘disproportionate’ to the amount of tissue damage, the patient is categorized as ‘psychogenic’, that is, the pain is ‘unreal’ and, therefore, emotionally based. The third edition of the American Psychiatric Association Diagnostic and Statistical Manual (1980) epitomizes this approach in its classification of Psychogenic Pain Disorder as a Somatoform Disorder. The diagnostic criteria for this disorder include: (a) no organic pathology or pathophysiological mechanism can be found to account for the pain, (b) the pain complaint is grossly in excess of what would be expected from the physical findings, (c) psychological factors are judged *Unfortunately, many writers in the area of chronic pain have incorrectly, even from a psychiatric dctinition (Hinsie and Campbell, 1976) equated functional with ‘psychogenic’ or emotional. The medical usage of the word functional relates to physical performance or execution (Bennington, 1984). Thus, functional pathology relates to a disturbance in the operation or performance of an organ or organ-system and can occur with or without associated changes in structure (Stedman, 1982). Throughout this article we will adhere to the medical definition of functional pathology and reserve the term ‘psychogenic’ to reflect emotional etiology.

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to be etiologically involved in the pain, and (d) the pain enables the individual to avoid some activity that is noxious to him or her. The dichotomous organic-psychogenic distinction makes several questionable and unwarranted assumptions. First, it assumes that there are adequate means for reliably measuring the amount of pain and normative data are available for various pain syndromes against which to compare an individual’s reports of pain in order to determine whether they are ‘excessive’. In addition to not specifying that medical evidence has to be present in order to determine that there is an organic basis for the pain, there is also an assumption that current medical and diagnostic procedures are capable of identifying all sources of pathology likely to cause the pain reported by the patient (Turk and Rudy, 1986). It is further assumed that there are no individual differences other than psychopathological ones that influence perceptions of noxious sensations. Finally, it is assumed that a psychiatric problem and a pain disorder cannot co-occur in the same individual or that a psychiatric problem cannot result from a chronic physical disorder. More recently, there has been an attempt to create yet another category within the psychiatric nomenclature, ‘pain-prone personality’, and to include it within the depressive-spectrum disorders (see Blumer and Heilbronn, 1982; Kane, 1977). According to this approach, based on historical factors (e.g. familial alcoholism, child or spouse abuse), chronic pain patients without sufficient, identifiable organic pathology were predisposed to develop ‘psychogenic pain’ as a form of masked depression. Empirical data to support the contention of a ‘pain-prone’ individual are inadequate and largely non-existent (Turk and Salovey, 1984) and recent research seriously challenges this conceptualization of chronic pain (e.g. France and Krishnan, 1985; Large, 1986). Traditional psychiatric instruments (e.g. Minnesota Multiphasic Personality Inventory (MMPI), Rorschach Inkblot Test, Szondi Test, Symptom Checklist-90) as well as psychiatrically-oriented assessment procedures specifically developed for chronic pain patients (e.g. Pain Apperception Test, Petrovich, 1958; Low Back Cognitive Distortion Scale, Lefebvre, 1981; Lb [low back] scale derived from the MMPI, Hanvik, 1951; Back Pain Classification Scale, based on the McGill Pain Questionnaire, Leavitt, 1983) have been employed in an attempt to identify subgroups of pain ‘low-back losers’, the ‘Conversion-V’ profile, ‘depatients (e.g. hysteroid-depressed-somatizers, niers’, ‘malingerers’). These patient classifications are then used to compare patient groups on medical findings and treatment outcome. Needless to say, because of the vagueness of some of these patient profiles and the difficulty in empirically operationalizing these constructs, their relationship to medical findings and outcome have been equivocal, at best. By far the most commonly employed psychopathologically-oriented standardized assessment instrument is the MMPI and its use in the assessment of chronic pain patients is no exception. Nearly 90 papers have been published identifying ‘profiles’ of pain patients that are then related to differential responses to treatments such as surgery (e.g. Pheasant, Gilbert, Goldfarb and Herron, 1979; Wilfling and Klonoff, 1973; Wiltse and Rocchio, 1975). The use of the MMPI for these purposes has been strongly criticized because of the dated original norms, the overlap of physical symptoms that are part of chronic pain with some of the MMPI scales, and the logic of this approach per se (e.g. Main, 1985; Naliboff, Cohen and Yellen, 1982; Rook, Pesch and Keeler, 1981). The debate on the utility of the MMPI in prediction of treatment outcome for chronic pain patients continues despite the variability and instability of profiles identified and contradictory and inconsistent findings (e.g. Hoon, Feuerstein and Papciak, 1985). This has led Naliboff et al. (1982) to conclude that the data do not support attempts at defining a low back pain or chronic pain personality profile apart from the emotional disturbance associated with chronic limitation and disruption of activity. Although personality instruments specifically developed for use in assessing individual differences among chronic pain patients may be more appropriate and useful than general psychiatric screening instruments, some of these instruments, although displaying promising psychometric properties, have not been cross-validated on additional pain populations (e.g. The Lb scale, Leavitt, 1982; Pain Apperception Test, Ziesat and Gentry 1978). Others remain preliminary and need basic psychometric work before their utility can be determined (e.g. Back pain Classification Scale, Leavitt, 1983; Mensana Clinic Test for Chronic Back Pain, originally the Hendler lo-minute Back Pain Screening Test, Hendler, Viemstein, Gucer and Long, 1979).

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assessment

Based on the observation that chronic pain patients display large individual differences in response to injury and treatment, behaviorally-oriented psychologists have suggested that pain is a subjective phenomenon and, consequently, all that can be observed are behaviors emitted in response to the subjective experience of pain. Thus, behavioral manifestations are viewed as the means by which patients communicate pain and suffering and it is these behaviors that should be assessed. According to Fordyce (1976) ‘pain behaviors’ include: (a) verbal complaints of pain and suffering, (b) nonlanguage sounds (e.g. moans, sighs), (c) body posturing and gesturing (e.g. limping, rubbing a painful body part or area), and (d) display of functional limitations or disability (e.g. reclining for excessive periods of time, i.e. ‘downtime’). The formulation of pain behaviors emphasizes that these behaviors are, by definition, observable and consequently measurable, It has been suggested that pain behaviors may provide a more objective means of assessing pain than patients’ self-reports that may be purposely distorted. Thus, systematic assessment of pain behaviors should contribute to the understanding of the pain experience and might be used as objective dependent measures in evaluating the efficacy of treatment interventions. In addition, the pain behavior construct has had useful heuristic value in the investigation of social learning factors in the development and maintenance of chronic pain problems. Based on Fordyce’s (1976) operant conditioning formulation of pain behaviors, several attempts have been made to develop assessment procedures to assess these behaviors. Somewhat paradoxically, the earliest attempts to assess behavior associated with chronic pain were based on the self-reports of patients. For example, patients were asked to keep diaries of the number of hours that they spent sitting, standing, reclining, and moving and to report on the quantity and frequency of medication use. Alternatively, pain behaviors have been determined based on information gathered during structured interviews regarding activity and medication use (e.g. Block, Kremer and Gaylor, 1980). Recently, more sophisticated approaches to the assessment of pain behaviors have been developed. One approach consists of the observation of a range of behaviors (Keefe and Block, 1982) or predetermined specific behaviors (e.g. facial expressions, Craig and Prkachin, 1983) that are measured during a structured set of activities (e.g. Keefe and Block, 1982). Alternately, these behaviors may be observed during a brief, unobtrusive time interval (e.g. Richards, Nepomuceno, Riles and Suer, 1982). A somewhat different approach has emphasized the use of electromechanical recording apparatus to directly monitor physical activity (e.g. Follick, Ahem and Laser-Wolston, 1984; Sanders, 1980). Although these newer approaches to pain behaviors assessment are advance:, over reliance on self-reports, limitations remain. Six common problems characterize all of the recent attempts to assess pain behaviors. (1) Investigators do not pay adequate attention to the specific characteristics of the pain behavior construct. In other words, identification of consensually agreed upon examples of the construct are not provided. (2) Specific measurement techniques to reduce assessment reactivity, increase assessment reliability, and insure assessment comprehensiveness are usually not provided. For example, who makes the observations (e.g. psychologist during an interview, nurse during rounds, or a physician following a physical examination that may exacerbate symptoms) can have a strong influence on the behaviors observed. (3) Some behavioral assessment procedures have limited content validity, that is, they are restricted in terms of what is observable. For example, mechanical recorders cannot record audible and facial indications of distress and observation procedures cannot sample activities during long periods of time (see Turk, Wack and Kerns, 1985a). (4) For a behavioral assessment procedure to be of clinical utility it must have some degree of generalizability. Thus, unless behavioral assessment is used clinically for specific patient needs, a behavioral assessment procedure that, for example, only discriminates pain behaviors in a specific environment, at a specific time of day, and so forth, may be of limited utility in establishing assessment norms that can be applied across a range of pain patients and clinical settings.

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(5) The touting of pain behavior assessment methods as ‘objective’ is somewhat misleading because pain behaviors, like self-reports, are under voluntary control and thus similarly susceptible to presentation bias. (6) Pain behaviors often are considered to represent a unidimensional construct. Recent research that employed advanced multivariate approaches indicates that this is not the case (e.g. Philips and Jahanshahi, 1986; Turk et al., 1985a). Although the development of more objective assessment of pain behaviors is an important advance and should enhance the pain assessment armamentarium, it is important to acknowledge that the evaluation of pain behaviors is, like measures of pain intensity, psychopathology, or traits, unidimensional. Assessment of pain behaviors should be viewed within the broader context of the evaluation of chronic pain patients that also includes examination of cognitive, affective, psychosocial, and other behavioral factors (e.g. activities of daily living), as well as physiological factors, all of which contribute to the total experience of chronic pain.

ASSESSMENT

OF

PSYCHOSOCIAL

FACTORS

If we accept that chronic pain is a complex, subjective phenomenon that is uniquely experienced by each patient, then knowledge about patients’ idiosyncratic appraisals of their plight, their unique experience of pain, and their coping resources (e.g. personal, financial, social support) become critical for optimal assessment and subsequent treatment planning. For example, patients’ subjective evaluations of the impact of pain on their lives are likely to be important factors in determining motivation for treatment and treatment adherence (Turk, Meichenbaum and Genest, 1983). Additionally, patients’ perceptions of their life circumstances are likely to influence their communications with significant others and health-care professionals. These sources of communication will influence how others respond to them and potentially the therapeutic modalities to which people with pain are exposed. Comprehensive assessment instruments specifically designed to evaluate the psychosocial dimension of chronic pain have begun to appear (e.g. Sickness Impact Profile, Bergner, Bobbit, Carter and Gilson, 1981; Illness Behavior Questionnaire, Pilowsky and Spence, 1975, 1976; West Haven-Yale Multidimensional Pain Inventory [MPI], Kerns, Turk and Rudy, 1985), as have more specific instruments that can be used to assess specific psychosocial factors such as coping repertoire (Rosensteil and Keefe, 1983). Detailed description of each of these instruments is beyond the scope of this paper (see Turk and Kerns, 1985; Turk and Rudy, 1986), however, we will describe one assessment instrument, the MPI, to illustrate recent attempts to assess, comprehensively, psychosocial factors related to the chronic pain experience. The MPI (Kerns et al., 1985) is comprised of three parts. The first two parts are related to patients appraisals of pain and the impact of pain on different domains of their lives and perceptions of the responses of significant others to their distress and suffering. The last part relates to the frequency that patients indicate specific behaviors are performed or not performed because of their pain. The first two parts are directly related to psychosocial variables. Part I was specifically designed to assess: (a) chronic pain patients’ reports of pain severity and suffering; (b) their perceptions of how pain interferes with their lives, including interference with family and marital functioning, work, and social-recreational activities; (c) dissatisfaction with their present levels of functioning in each of the areas listed in (b); (d) appraisal of the support provided by spouses, family, and significant others; (e) perceived life control, incorporating the perceived ability to solve problems and feelings of personal mastery and competence; and (f) affective distress, including ratings of depressed mood, irritability, and tension. Part II consists of ratings by patients of the frequency with which significant others respond to their expression of pain by (a) punishment (e.g. irritability, ignoring), (b) solicitousness (e.g. takes over their chores), and (c) distraction (e.g. encourages them to work on a hobby). Instruments such as the MPI, that have satisfactory psychometric properties and provide norms that have been specifically established for pain patients, are an important advance (Kerns et al., 1985). Used alone, however, they still address only one general aspect of pain. Thus, they can contribute but are not adequate by themselves for the comprehensive assessment of pain patients.

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PRELIMINARY

ATTEMPTS

AT INTEGRATING

ASSESSMENT

FINDINGS

An important first step, the McGill Pain Questionnaire The advent of multidimensional views of pain, most notably contained within the Gate Control model (Melzack and Wall, 1965), has led to efforts to quantify pain along several separate yet related dimensions. For example, Melzack and Casey (1968) suggest that pain is more than a simple sensation but rather pain is a complex perceptual process comprised of cognitive and affective components in addition to a sensory factor. The distinction between perception and sensation has been endorsed by the International Association for the Study of Pain (IASP, Committee on Taxonomy, 1979, 1986), who suggest the term pain be reserved for the perception of pain and the term nociception be used for sensory stimuli capable of being perceived as pain. Assessment of the perception of pain, then, would require assessment of each of the relevant components or dimensions of the pain experience. Based on the Gate Control model, Melzack (Melzack, 1975; Melzack and Torgerson, 1971) developed the McGill Pain Questionnaire (MPQ) as an attempt to operational& a threedimensional assessment approach. The most relevant section of this instrument focuses on the quantification of sensory-discriminative, motivational-affective, and cognitive-evaluative components of the pain experience by examining the specific verbal pain descriptors endorsed by patients. Turk, Rudy and Salovey (1985b) found that the three separate scales, however, did not demonstrate discriminative validity and suggested that this instrument was actually only measuring one primary construct, pain intensity. Other verbal descriptor approaches have been developed in an attempt to quantify the multidimensional aspects of the pain experience (e.g. Gracely, McGrath and Dubner, 1978; Tursky, Jamner and Friedman, 1983). These alternate assessment methods have not received widespread clinical use as has the MPQ, possibly because they are more cumbersome and have their greatest utility in the laboratory (see Chapman, Casey, Dubner, Foley, Gracely and Reading, 1985). The advent of multi-instrument

assessment

With increasing recognition that chronic pain can impact on the patient in many ways (e.g. emotionally, socially, physically, vocationally), investigators and clinicians have begun to assess the chronic pain patient with a plethora of measures. Although this is a step in the right direction and leads to a more comprehensive evaluation of the pain patient, the difficult task is to integrate such large quantities of data in meaningful ways. One solution is for the investigator to conduct a data reduction strategy to achieve some general understanding of the factors that are of special importance or unique to the chronic pain patient. A number of data reduction approaches have been proposed. These include (a) dividing scales at their median point to create 2-by-2-type table arrangements (e.g. Brena and Koch, 1975), (b) creation of aggregate scores by summing scale scores (e.g. Bergner et al., 1981; Waddell et al., 1980), and (c) computing factor scores based on the interdependencies of the scales (e.g. Naliboff et al., 1985). Multidimensional versus multiaxial. Despite the growing awareness of the importance of conducting multidimensional assessments, a multidimensional assessment may be viewed as uniaxial if it only considers medical, psychosocial, or behavioral information separately. For example, the use of the MMPI in evaluation represents a multidimensional assessment in that it considers multiple measures of psychopathology but remains uniaxial because it only focuses on psychopathology. To date, there have been few attempts to develop a comprehensive, empiricallybased integration of physical, psychosocial, and behavioral evaluation findings, that is, a multiaxial approach to assessment. Although some investigators have begun to utilize evaluation and assessment approaches that can be considered multiaxial, these authors, however, have not combined or used data analytic approaches that simultaneously take into consideration their multiaxial findings. We will describe three separate approaches in order to contrast the most commonly used integration strategies. The Emory Pain Estimate Model Perhaps the first attempt at integration was initiated by Steven Brena and his colleagues (Brena and Koch, 1975; Brena, Koch and Moss, 1976). Brena developed a two-dimensional strategy that

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is referred to as the Emory Pain Estimate Model (EPEM). The dimensions are somewhat arbitrarily labelled ‘pathology’ and ‘behavior’. The pathology dimension includes the quantification of physical examination procedures (e.g. ratings of joint mobility and muscle strength) as well as assigning numerical indices to reflect the extent -of abnormalities determined from diagnostic procedures such as radiographic studies. The behavioral dimension is a composite of activity levels, pain verbalizations, drug use, and measures of psychopathology based on elevated MMPI scales. Using median divisions on the pathology and behavior dimensions, the EPEM defines four ‘classes’ of chronic pain patients. Class I patients are characterized by higher scores on the behavior dimension and lower scores on the pathology dimension. These patients are described as displaying low activity levels, high verbalizations of pain, prominent social and psychological malfunctions, and frequent misuse of medications (Brena, 1984). Class II patients are those who display lower scores on both dimensions. These patients are described as displaying highly dramatized pain complaints with ill-defined anatomical patterns who, however, do not display significant behavioral malfunctions. Class III is comprised of patients with higher scores on both the pathology and behavioral dimensions. Brena characterizes these patients as those pain patients who show clear evidence of a pathological disorder and high intensity illness behavior. Finally, Class IV patients are those who have higher scores on the pathology dimension and lower scores on the behavior dimension. These patients are described as those demonstrating competent coping in the presence of a demonstrable pathological condition. Although Brena and his colleagues have appropriately emphasized the importance of integrating physical and psychological assessment data in order to develop a classification system for chronic pain patients, some of the basic characteristics of the EPEM are problematic. From a conceptual and theoretical standpoint, the inclusion of activity levels, pain verbalizations, and measures of psychopathology under a single dimension labelled ‘behavioral’ is conceptually problematic. Additionally, neither of the dimensions incorporate psychosocial information likely to play an important role in chronic pain (Turk et al., 1983; Turk, Rudy and Boucek, 1987). For example, patients’ appraisals of the impact of pain on various domains of their lives, levels of social support, and how that support relates to their ability to cope with chronic pain is not addressed. Examination of the scoring and classification system employed in the EPEM highlights additional problems. For example, the weights assigned to specific medical-physical findings were based on an a priori weighting system and were not empirically derived. Also, applying median divisions to the two dimensions, although intuitively appealing, artificially creates four clusters of patients. That is, there is no statistical demonstration that four non-overlapping groups of pain patients ‘naturally exist’ in these data or that, in fact, the pathology and behavioral dimensions are independent. Visualization of the 2-by-2 grid presented by Brena and his colleagues (Brena and Koch, 1975; Brena and Chapman, 1982) reveals that extreme scores are treated the same as scores near the medians. This method of establishing a taxonomy of pain may lead to erroneous or non-independent patient classifications because it is derived from artificial and external criteria rather than from divisions or clustering that occur naturally within patients’ scores. In sum, Brena and his colleagues are conceptually correct and have been ahead of their time by advocating a multiaxial approach to the assessment of pain patients. However, the measures used to operationalize the EPEM and the quantitative methods used in its development preclude its aceptance as a viable multiaxial and taxometric system for chronic pain assessment. The Waddell approach

Although not intended to be a patient classification system as in the EPEM approach, research by Waddell and his colleagues (Waddell and Main, 1984; Waddell, Main, Morris, Paola and Gray, 1984; Waddell et al., 1980) have addressed the interdependencies among physical and psychological assessment findings in chronic low back pain patients as well as how these findings relate to illness behavior. A central theme of this research has been to evaluate the association between ‘objective’ physical impairment and ‘subjective’ disability. Waddell and Main (1984) utilizing factor analytic procedures, identified nine basic physical activities in daily living frequently restricted by low back pain (e.g. lifting, sitting, walking, sleeping). Patients’ reports of their loss of ability or limitations on these activities are recorded in an interview format and are used to form a chronic disability index. This index is then related to clinical findings of physical impairment, which is comprised

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of physician ratings related to the appropriateness or inappropriateness of patients’ descriptions of their pain pattern, evaluation of patients’ degree of lumbar flexion, straight leg raising, root compresion signs, and previous lumbar surgeries. It is interesting to note that other physical characteristics, for example, pattern of injury, physical signs of deformity, muscle tenderness, other spinal movements, and radiological findings of degeneration, did not improve upon their physical impairment index. Regression analyses designed to address the association between physical impairment and disability indicated that the physical impairment index accounted for less than half of the variance in the disability index, which also can be substantialy influenced by psychosocial and behavioral factors. These findings were confirmed in a related study (Waddell et al., 1984) that indicated 40.3% of the disability index was accounted for by the physical impairment index, psychological distress (i.e. depression and increased bodily awareness) accounted for an additional 22.5% of the variance in disability, and magnified illness behavior (i.e. inappropriate symptoms and signs) accounted for an additional 8.4% of the variance. In sum, although in its present form the work of Waddell and his colleagues does not lend itself to an integrated, multiaxial taxonomy of chronic pain patients, it does highlight that multiaxial findings can be studied in systematic ways. The Pittsburgh multiaxial approach

Although the data reduction methods described earlier are appealing, they can create arbitrary, biased, or artificial patient groupings and thus are not acceptable taxometric methods (Meehl and Golden, 1982). Recently, at the Center for Pain Evaluation and Treatment at the University of Pittsburgh we have begun to examine the utility of quantitative taxometric and empirically-derived classification procedures to integrate psychosocial, behavioral, and physical findings. The primary purposes of our investigations have been to find efficient methods to summarize and organize multiaxial pain assessment data, to elucidate patterns within these assessment data, and to assess the reliability and validity of an empiricaly-derived taxonomy of chronic pain patients. We will summarize below the development of the Pittsburgh Multiaxial Assessment of Pain (MAP). Before describing the MAP approach, however, it should be emphasized at the present time this assessment approach is exploratory and descriptive in nature. Although eventually this approach may lead to a more objective and complete diagnosis of chronic pain patients and subsequent prognostic predictions and differential treatment planning, as with any taxometric system, extensive clinical and empirical evaluation of the utility of the MAP system will need to be conducted before it can fill this role. The taxometric evaluation of the Multidimensional Pain Inventory. The Multidimensional Pain Inventory (MPI; Kerns et al., 1985), described earlier, was used in the initial phase of taxometric development. This instrument was selected because it is a comprehensive, psychometrically-sound inventory that adheres to the perspective that chronic pain is a complex, subjective phenomenon that is uniquely experienced by each patient. It was felt that the MPI was particularly suited to the development of an accurate and reliable patient classification/taxometric system because, in addition to measuring reports of pain severity, dysphoric mood, and daily activity levels, the MPI also contains measures of patients’ subjective evaluations of the impact of pain on their lives. Additional strengths of the MPI include its content validity (it was developed on and for chronic pain patients), its economy of administration and scoring, and its sensitivity to treatments effects (e.g. Barrios, Niehaus and Henke, 1986; Kerns, Turk, Holzman and Rudy, 1986). Utilizing recent statistical advances in clustering techniques that increase the accuracy of these methods (e.g. Milligan and Cooper, 1985; Scheibler and Schneider, 1985), cluster analyses were conducted on the MPI scales from a heterogeneous group of 122 patients to determine whether there were different response patterns that classified patients into unique groups. The k-means clustering approach was used to discover more about the similarities and difference among chronic pain patients in order to identify subgroups or ‘homogeneous’ samples of pain patients and to guard against our superimposing an a priori but potentially invalid structure to the data. Three distinct patient profiles were identified by means of this analysis. These group profiles were labelled (1) ‘Inadequate Social Support’, patients with a common perception that significant others were not very understanding or supportive of their problems; (2) ‘Globally Dysfunctional’, patients who perceived the severity of their pain to be high, reported that pain interfered with much of their

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lives, reported a higher degree of psychological distress due to pain, and reported low levels of activity; and (3) ‘Adaptive Responders’, patients who reported high levels of social support, relatively low levels of pain and perceived interference, and greater amounts of activity. The external validity of these clusters was assessed by testing whether these three groups of patients scored differently on measures other than the MPI (e.g. McGill Pain Questionaire, Melzack, 1975; Beck Depression Inventory, Beck et al., 1961). Multivariate and univariate analyses of variance of over 10 reliable, external scales supported the uniqueness of each of the three clusters of patients. Discriminant function analyses were used to assess the distinctiveness of the three clusters and classification power of the MPI. Two highly significant functions resulted (P < 0.0001). Using multivariate classification procedures that adjusted for the intercorrelations of the MPI scales indicated that only four of the 122 cases (3.3%) were misclassified. Computation of the tau coefficient (Klecka, 1980) indicated that the MPI scales made 95% fewer errors in cluster classification than would be expected by random assignment. As a further test of the validity and uniqueness of the three patient profiles, the MPI scale scores from a second population of 79 chronic pain patients were used to test the generalizability of these findings. The group means and covariance matrices on the MPI from the first pain population were used to compute generalized multivariate distance functions for each of these 79 patients. Using a >0.70 posterior probability of group membership rule (0.33 would be expected by chance alone), this empirically-based classification procedure indicated that only five of the 79 patients in the second population could not reliably be assigned to one of the three patient profiles. The average probability of group membership for cases classified into the three patient clusters, Inadequate Social Support, Globally Dysfunctional, Adaptive Responders, was 0.91, 0.87, 0.93 respectively, Additionally, the percentage of patients classified into each of the three patient profiles (28, 43, and 29%, respectively) was virtually identical to the percentages observed in the first patient population. Medical procedures used to evaluate chronic pain patients. To this point, we have only considered two of the three relevant dimensions that we believe should form the basis of a multiaxial system for the assessment of chronic pain patients, namely, psychosocial and behavioral. As noted earlier, a frequent source of confusion in the medical evaluation of chronic pain patients relates to what clinical and laboratory findings are useful and appropriate for chronic pain patients, how much importance should be given to each result, and how to reliably assess physical pathology. A common difficulty in comparing research across multiple studies is that investigators often make determinations of the degree of medical pathology based on different assessment procedures and criteria. For example, is determination of the clinical pathology based on plain radiographic and electromyographic findings equivalent to determining pathology based on physical examination? Should computed axial tomography (CT scans) be given more importance than physical examination in the medical evaluation of pain patients? Should a structurally-oriented finding be given more weight than a funcitonally-oriented finding even though the structural finding may be less reliable than the functional finding?

Table 1. Average rank-ordering of 18 common medical-physical procedures used in pain assessment 1.

2. 3. 4. 5. 6. 7. 8. 9. 10. II. 12. 13. 14. 15. 16. 17. 18.

Neurological examination Observation of gait and posture Examination of muscular function (tone, mass, strength) Assessment of spinal mobility Examination of soft tissues Assessment of mobility of weight-bearing joints Plain radiography Assessment of mobility of joints other than spine or weight-bearing crscan Electromyography Contrast radiography Examination of internal organs (inspection, palpation, auscultation, percussion) Nuclear medicine Laboratory tests (other than blood count) Thermography Blood count Electrocncephalography Electrocardiography

246

DENNLYC. TURKand THOMAS E. RUDY

To begin to address these questions we recently conducted a pilot study to establish the differential utility of the most commonly employed diagnostic procedures used by algologists (physicians specializing in the assessement and treatment of pain patients). Eighty members of the American Academy of Algology were surveyed to establish the differential utility of 18 frequently used diagnostic tests and examination procedures (e.g. electromyography, spinal mobilty-see Table 1). These physicians displayed a high degree of agreement (Kendall’s coefficient of concordance = 0.65, P
Multiaxial assessment of pain PS

35 ’

PS I

247

I

LC

AD

S

PR

SR

DR

GA

PF

I I

LC I

AD I

S I

PR I

SR I

DR I

GA I

PF I

Fig. 1. Mean T-scores for patient protiles on the MPI and physical findings. PS = pain I = interference, LC = life control, AD = affective distress, S = support, PR = punishing responses, SR = solicitious responses, DR = distracting responses, GA = general activity, and PF = physical findings

Cluster IV. The resulting four-profile solution did not produce a significant loss in classification accuracy. New classification functions that included medical-physical findings indicated only three of the 46 patients were classified into an incorrect cluster and the tau index was computed to be 0.94, indicating that 94% fewer errors in profile classification occurred than would be expected by random assignment. The mean scores on the MPI and medical-physical index for each of the four patient clusters are plotted in Fig. 1 as T-scores (Mean = 50, SD = 10). These four patient profiles resulted in 30.4% of patients being classified into Cluster I, and 23.9, 21.8, and 23.9% being assigned to Clusters II, III, and IV, respectively. In sum, these findings indicate that a reliable, valid, and objective multiaxial classification procedure, based on sound taxometric methodology, can be developed for chronic pain patients. Additional research is required to examine the incremental validity of behavioral observation of pain behaviors, coping resources (Rosentsteil and Keefe, 1983), idosyncratic cognitive styles (Lefebvre, 198 1) and more mathematically-sound weighted scoring systems for medical-physical findings. The goal should be the development of a triarchic, Multiaxial Assessment of Pain (MAP) that will enhance our understanding of pain, assist in evaluation and the prescription of specific therapeutic interventions, and further our ability to predict treatment outcome. Information based on a MAP-type system should be incorporated within the taxonomy of chronic pain syndromes recently proposed by the International Association for the Study of Pain (IASP Subcommittee on Taxonomy, 1986). The days of scales without acceptable biometric or psychometric properties, evaluation instruments that have not been normed on chronic pain patients, as well as assessment methods based on unidimensional conceptalizations of chronic pain patients seem numbered if the field hopes to make significant advances. It seems to us that health care professionals will be abrogating their responsibilities if they attempt to provide treatment for chronic pain patients without appropriate consideration and integration of the medical-physical, psychosocial, and behavioral dimensions in their treatment planning. in

Correspondence-Requests

for reprints should be addressed to Dr Dennis C. Turk.

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