Chronic pain

Several important organizations in the United States have now developed new standards for the evaluation of pain. For example, the Joint Commission on Accreditation of Healthcare Organizations (JCAHO)16 requires that healthcare professionals consider pain to be a fifth vital sign (added to pulse, blood pressure, core temperature, and respiration) when evaluating patients. As reviewed by Gatchel and Oordt,2 the JCAHO guidelines require that pain severity be documented using a pain scale. Moreover, the following also need to be assessed:

• the patients' own words describing their pain;

• the location of the pain and its duration, as well as aggravating or alleviating factors;

• present pain management regimen and its effectiveness;

• a physical examination.

As noted by Gatchel,1 it is now recognized that the most comprehensive and heuristic approach to the assessment and treatment of chronic pain is the biopsychosocial perspective. This biopsychosocial model focuses on the complex interaction among biological, psychological, and medicolegal variables that patients encounter when dealing with a persisting, distressing, chronic pain condition. Such an interaction may perpetuate, and even worsen, the clinical presentation. It accounts for the likelihood that patients' lives are adversely affected in a variety of ways by their chronic pain condition, thus requiring a comprehensive assessment and treatment approach designed to address all aspects of required care, both biological as well as psychosocial. As noted earlier, this approach is in stark contrast with the outdated, overly simplistic biomedical reductionist approach which mistakenly assumed that most pain disorders could be broken down into distinct, independent physical and psychosocial components. There is often an absence of a documentable association between pain and a patho-physiologic process in the organ or body part from which the pain is perceived as emanating.

Each individual will experience a chronic pain condition uniquely. The complexity of such conditions is especially evident when it persists over time, as a range of psychological, social, and economic factors can interact with physical pathology to modulate a patient's report of discomfort and disability associated with the chronic pain. It is therefore essential to comprehensively evaluate all these major components for each individual in order to subsequently tailor a unique treatment program to account for his or her specific needs.

What are some of the commonly used measures of chronic pain? A visual analog scale (VAS) has traditionally been one of the most widely used self-report measures of pain. For example, the Million VAS (MVAS) is a 15-item measure designed to assess pain, disability, and physical functioning, and it is useful primarily for patients with chronic low back pain disorders.17 It provides a simple, easy-to-understand format for patients. In a recent study,18 MVAS scores were used to categorize patients into one of six groups: no reported pain/disability (score of 0); mild pain/disability (score of 1-40); moderate pain/ disability (score of 41-70); severe pain/disability (score of 71-100); very severe pain/disability (score of 101-130); and extreme pain/disability (score of 131-150). Using this categorical method, it was found that this measurement was related to several important outcomes, such as treatment dropout rate and level of depression, as well as one-year socioeconomic outcomes (such as return-to-work rate, work retention, post-rehabilitation surgeries, etc.). Such results indicate that the use of the MVAS scores as categorical indices is effective in predicting treatment outcomes in patients with chronically disabling spinal disorders. Of course, a more general VAS instrument can be used for types of pain other than low back pain.

In fact, a recent measure developed by Anagnostis et al.19 evaluates functional status due to pain and disability - the Pain Disability Questionnaire (PDQ). The PDQ yields a total functional pain and disability score ranging from 0 to 150. The focus of the PDQ, much like other health inventories, is primarily on pain, disability, and function. Unlike most other measures, though, the PDQ is also designed for the full array of chronic pain disorders, rather than purely one type of pain, such as low back pain. Psychosocial variables, which recent studies have shown play an integral part in the development and maintenance of chronic pain and disability, form an important core of the PDQ. The psychometric properties of the PDQ are excellent, demonstrating stronger reliability, responsiveness, and validity relative to many other existing measures of functional status, such as the Oswestry, the MVAS, and the SF-36 instruments. A factor analysis of the PDQ revealed two independent factors that can be evaluated: a functional status component and a psychosocial component. Analyses demonstrated each of these two components to be valid in assessing their theorized constructs.

Of course, one of the most widely used self-report measures is the Medical Outcomes Study 36-Item Short Form (SF-36), which was developed for various uses in clinical practice and research.20 It is a good global index of patient functioning and measures the functional status of the whole patient. The SF-36 has eight scales that measure health concepts: physical function, role limitation because of physical health problems, bodily pain, social functioning, general mental health, role limitation because of emotional problems, vitality, and general health perception. There are also two global summary or component scales: a physical component summary scale and a mental component summary scale. Lower scores on the mental component scale are usually a good index of potential emotional distress; low scores on the physical component scale are usually a good index of potential physical function limitations. The advantages of the SF-36 are that it is brief (taking approximately 10-20 minutes to complete), and it divides health into distinct physical, social, and mental components. An even shorter form, the SF-12, is now available. One shortcoming, though, is that the actual clinical usefulness of the SF-36 with individual patients is not well established because of these test's psychometric properties. However, it can be used to monitor overall group changes.

In addition to the above, there are many other measures of chronic pain that can be used. The reader is referred to Turk and Melzack10 and Gatchel1 for a comprehensive review of these various measures.

Many of the above measures used for assessing chronic pain are often also used to measure degree of self-reported disability (see below under Disability). Indeed, for example, the PDQ was developed specifically for evaluating self-reported pain, as well as disability. Such questionnaires were designed to assess a patient's degree of functional status, disability, as well as pain that would interfere in activities of daily living. There are also other self-report measures that evaluate more specific on-the-job disability limitations and work performance. For example, the Work Limitations Questionnaire (WLQ) scale developed by Lerner and colleagues21 assesses limitations in handling work-time demands, work-physical demands, mental-interpersonal demands at work, and output demands. The full instrument is 25 items, divided into four scales. Each WLQ scale score is interpreted as the percentage of time in the previous two weeks that a person was limited in performing a specific class of job demands. Scores are the means of nonmissing responses and converted to a range of 0 (no limitations) to 100 (limited all the time). An algorithm is available from the developer to convert these percentages to projected economic losses in a cross-sectional study of a general working population. The psychometric properties of this instrument are good.

Another instrument developed to measure human performance indices of disability is the Spinal Function Sort (SFS), which is a 50-item, paper-and-pencil, self-report questionnaire that assesses ability to perform physical tasks.22 This instrument is used to identify functional consequences of disability and medical intervention. On the SFS, the evaluee ranks ability to perform 50 common physical tasks depicted by drawings and text captions on a six-point scale. The "rating of perceived capacity'' is an estimate of work capacity in terms of the United States Department of Labor Physical Demands Characteristics System for people who have experienced soft tissue musculoskeletal injury. It is administered as a stand-alone evaluation or as part of a more comprehensive functional capacity evaluation. Again, the reader is referred to Turk and Melzack10 and Gatchel1 for fuller descriptions of a variety of other evaluations such as these.

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