Is It Time To Change the Way We Report Pain?
“Although we all know that pain is multidimensional, we still often measure it on a 0 to 10 scale because that is quick and simple for both the patient and the doctor. This oversimplification doesn’t seem to match our understanding of pain and doesn’t seem to address a patient’s true quality of life. What other options exist for measuring pain, especially if we are documenting reductions for clinical studies and future reimbursement changes?”
– Measured in Manhattan
image You have voiced a concern that is shared by almost all pain physicians. All of us have seen patients who had dramatic improvements in their quality of life from an intervention, but fail to report a dramatic change in the numerical rating scale (NRS). I can think of an elderly patient with 9/10 pain who was bound to her home for much of the day. She underwent a series of epidurals and on follow-up was excited to report, “I have a life again.” She has been able to walk her dog every night, go to her church’s small group and is now planning a trip to see her grandchildren. She also was excited to report that her pain had decreased to 6/10, “the lowest it’s been in years.” If one were to track only her NRS, the intervention would appear to be a failure or to have provided minimal success (a 30% reduction in pain); clearly, however, the intervention has had a dramatic effect on her activities of daily living (ADLs) and her overall quality of life.
The way physicians and social scientists have measured pain has changed over the years, as our understanding about pain has grown. Melzack and Wall’s 1965 gate control theory of pain demonstrated the interaction between psychological and physiologic factors in the pain process.1 Gate control theory made it clear that a purely biomedical model was inadequate: Pain is more than just its physical neurologic aspects. Over time, our understanding became more complex. Today, the biopsychosocial model is the dominant approach to understanding pain. It considers the dynamic ways that physiologic, psychological and social factors interact in a patient’s experience of chronic pain.2 There are several physiologic aspects of pain that can be measured, including the regions of the body affected, systems affected, range of motion, pathophysiology, temporal characteristics, intensity and onset. It has been well documented that concurrent psychological variables affecting pain perception also are important to assess.3 Empirical support exists for three types of psychological variables that contribute to a patient’s experience of pain. These include affective factors, such as depression, anxiety and anger; cognitive factors, such as beliefs about pain, beliefs about controllability, self-efficacy, cognitive errors and coping; and sociocultural factors, such as social learning mechanisms, operant learning mechanisms and respondent learning mechanisms.4 The multifaceted nature of pain makes the reliable and valid assessment of it a daunting task.
Types of Measures for Clinical Use
Some scales focus specifically on pain intensity. Some commonly used scales are the verbal rating scale (VRS), visual analog scale (VAS) and the aforementioned NRS. Originated by Melzack, the VRS is a simple, commonly used categorical pain rating scale.5 Patients select one of multiple descriptors that represent pain of progressive intensity. Some common descriptors include none, mild, discomforting, distressing, horrible or excruciating. On the VAS, patients are asked to place a vertical mark, indicating their current pain intensity, on a 10-cm horizontal line anchored by no pain on one end and worst pain imaginable on the other. Pain severity is measured as the distance in centimeters between the zero position and the marked spot.6-8 On the NRS, patients are asked to provide their pain level using an 11-point scale, where 0 represents no pain and 10 represents worst possible pain.9 Studies have found that participants given the same stimulus of pain sometimes rate the severity of the pain differently.10 Additionally, the same participants’ responses on the VAS sometimes varied when presented with the same level of a painful stimulus at different times.10 This suggests that not all ways of measuring pain are reliable, and the VAS in particular may lend itself to less reliable results.
Some scales focus on aspects in addition to pain intensity, such as the short form McGill Pain Questionaire (SF-MPQ) and the West Haven-Yale (WHY) multidimensional pain inventory, both of which include affective and sensory descriptors associated with pain. The SF-MPQ and the WHY measure the patient’s pain experience, other’s reactions to the patient’s pain and ADLs.11,12 Although these scales offer a valuable integrative approach to pain assessment, they individually do not encompass all aspects of pain (e.g., sociocultural, cognitive and affective factors). Many pain medicine physicians use the simple NRS scale, given that tools such as the WHY and SF-MPQ are time-consuming and can be difficult to interpret.
A study by the Initiative on Methods, Measurement, and Pain Assessment in Clinical Trials (IMMPACT) found that, in addition to the importance of assessing pain relief and improvement in physical and emotional functioning, a comprehensive outcome measure must also consider changes in “fatigue, sleep, home and family care, social and recreational activities, interpersonal relationships, and sexual activities.”13 In 2005, IMMPACT recommended several core outcome measures to be used in clinical trials14; however, few of these measures were designed specifically to evaluate the efficacy of pain management treatments, or were normed on a pain population (e.g., Beck Depression Inventory, Profile of Mood States, etc.). Casarett et al15 found that in addition to the reduction of pain, patients commonly cited improvement in sleep and increased ability to function as meaningful clinical end points. Moreover, Robinson et al16 found patients considered decreased fatigue, distress and interference as indicators of treatment success.
In response to these concerns, the global pain scale (GPS) was created. The GPS was designed to capture the multidimensionality of pain but also to provide a single score that could be used to track changes (e.g., as the result of a clinical intervention).17 Rooted in the biopsychosocial model, the GPS assesses physical pain, affective effects of pain, specific clinical outcomes, and the degree to which the pain interferes with ADLs. Because the scale can provide one number encompassing each of these aspects, this allows clinicians to see the effects of interventions (e.g., a procedure might not initially reduce pain per se but increase mobility or reduce the need for medications—both clinically important outcomes that would not normally be measured in a pain assessment).
Although clinicians understand that pain and its effects are multidimensional, they also desire a single measurement to work with, which is why the simple NRS question, “What is your pain on a scale of 0 to 10?” is still the most-used scale, despite its shortcomings. It measures pain intensity but lacks psychological variables proven to be part of the patient’s pain experience4 as well as clinical outcome measures and ADLs.
Although we use several different approaches depending on a particular case, we tend to use the 20-item short form of the GPS most often. The scale was designed to provide answers to clinical questions, such as whether an intervention really makes a difference beyond a reduction in pain scores. Additionally, it seems to present the best balance between comprehensiveness, simplicity and speed of measurement. We frequently use it as a bedside assessment of baseline functioning, and as a repeated outcome measure for assessing change over time in both acute and chronic pain states (although most of our work focuses on chronic pain). The scale possesses great value in this circumstance, because it was designed to provide answers to clinical questions, such as whether an intervention really makes a difference beyond a reduction in pain scores.
In assessing physical pain states, the GPS addresses the ceiling, floor and average pain over the past week, as well as current pain state. In assessing the psychological effect of pain on the patient, the GPS screens for fear, depression, tiredness, anxiety and stress. The GPS explores several specific clinical outcomes, including the effect of pain on the patient’s quality of sleep, comfort, medication consumption, independence and work (or daily task) interference. Finally, the GPS assesses the patient’s perception on how the pain affects ability to complete several daily activities, including shopping at the grocery store, completing chores, enjoying the company of friends and family, exercising (including walking) and participating in hobbies.
In the interest of full disclosure, we must admit that several of the authors of this article were involved in creating the GPS, but it has been tested at Iowa State University and the results published in Pain Physician.17 This article presents the first reliability, construct validity and criterion validity tests from a sample of adults reporting chronic pain. The GPS demonstrated high criterion validity and high construct validity (including both convergent and discriminant validity). The criterion validity of the GPS was established by comparing it to two pain scales that have been previously validated for clinical work, the MPQ and the WHY. High correlations between similar subscales showed evidence of convergent validity for those scales, and lower correlations between dissimilar subscales showed evidence of discriminant validity. Additionally, construct validity was demonstrated by correlating the GPS with the Perceived Stress Scale, as high pain should predict higher life stress.
We believe the GPS can be used as a standardized measure of treatment efficacy. It uniquely tracks clinical outcomes after a pain-relieving treatment has been initiated. The GPS can be administered to the patient in the waiting room and scored by the support staff, thus resulting in a robust assessment of pain in one numerical score that the physician can employ to formulate treatment plans. For research, the GPS can be used to measure pain scores and to follow pain treatment efficacy. The GPS is available free for physicians’ use in their practices or research studies, at http://www.paindoctor.com/global-pain-scale.
Drs. Lynch and McJunkin own and operate Arizona Pain Specialists, a comprehensive pain management practice that provides minimally invasive, clinically proven treatments, with three locations in the greater Phoenix area. Drs. Lynch and McJunkin also provide consulting services to other pain doctors around the country through their partner company, Boost Medical. For more information, visit ArizonaPain.com and BoostMedical.com.
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