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A Review of the Evaluation of Pain Using a Variety of Pain Scales

Measurement of chronic pain is fraught with difficulty even under the most rigid research conditions. In an office setting designed to treat patients with chronic pain utilizing modern pain medicine interventional and non-interventional techniques, it is paramount that rapid patient driven assessment of pain is available to satisfy the medical legal and ethical aspects of treatment. There are many validated psychological tests available that include the assessment of chronic pain as subsets or scales; however the majority of these tests are too cumbersome and time-consuming for both the patient and physician in an office-based practice. It is important the physician understand the limitations of the rapid assessment tools that are commonly employed in an office setting.

Pain perception is a product of nociceptive input that is progressively modified at the spinal cord and brain levels to procedure a perception of pain, which may have little to do with the initial stimulus intensity. Pain is a high order conscious awareness of an unpleasant sensory perception after the nociceptive signals are processed. Most chronic or subacute pain is not a primitive impulse; however acute pain at the time of onset may more mirror a primitive unprocessed signal that serves as a warning for impending tissue injury, and evokes rapid behavior modification to remove the affected sensors from harm’s way. Other types of primitive pain may be those that travel in a diffuse, non-localizable pathway along the sympathetic fibers such as visceral pain. But most chronic pain is not primitive, and reflects a significant processing of the signal at multiple levels of the CNS.

Signal modulation and shaping can occur at many different levels including at the interneuron level of the spine, the thalamus, amygdyla, hippocampus, thereby engaging sensory, emotional, and cognitive processing areas of the brain. In turn, pain may cause changes in the affective, functional, and cognitive aspects of life.

Chronic pain is affected and modified by the following:

Culture (some societies express pain outwardly while some societies consider it rude to complain about pain) Environment (those having grown up with family members that focused on pain excessively or on a litany of treatments for pain accept such behavior as normal whereas forced stoicism during childhood may lead to unhealthy repression of any outwardly expression of pain) Emotional state/chronic psychological disease may affect the noradrenergic or serotonergic descending inhibitory pathways. Extreme anxiety and depression may significantly enhance pain perception. Anticipatory pain in patients that are depressed show activation of the amygdyla and decreased activation of the periaqueductal grey areas of the brain. [1] Sleep deprivation may produce a decrease in serotonin levels that act as a neurotransmitter in the monoaminergic descending inhibitory pathways. Impaired sleep due to pain or other reasons, may serve to amplify pain through serotonin depletion. Opiate effects that amplify pain causing a generalized perception of nearly constant pain in a dose dependent manner in a minority of patients. Gender has been found to be an inconsistent indicator of enhanced pain intensity for the same relative stimulus and the female population; however several studies have found this to be so. Patient related activities such as cigarette smoking or continued heavy labor with multiple re-injuries.

Defining pain is not something that is agreed upon by many patients. Numbness, weakness, elevated or decreased temperature in an area, focal dysesthesia, and anxiety may all be vehemently vocalized as pain since most patients lack the education to separate out the unusual but non-painful from the painful sensations. The IASP definition of chronic pain as any "unpleasant sensory or emotional experience associated with actual or potential tissue damage or described in terms of such damage unpleasant sensation" is equally nebulous. Under such a definition, a small area of numbness may be defined as painful by many people, emotional distress may be seen as pain, or even anticipating possible pain would be characterized as having pain. Therefore, intensity of perceived pain cannot exist in isolation of other descriptors that must accompany any such subjective description. The most extreme case of excessive simplification was adopted and codified by the JCAHO when they proclaimed "pain" as the "5th vital sign". The reduction of a multidimensional subjective perception that is shaded by all the factors defined above into a single scalar number by using a VAS or verbal description of pain in isolation of all other factors was a travesty. It required hospitals across the land to incorporate the totally subjective multidimensional perception into the matrix of objective vital signs used to ensure homeostasis, as though pain itself could somehow be accurately measured. To ascribe objective properties to pain would have the same effect as asking a person how they feel on a given day, and they reply with a number between one and 10. Pain clearly does not meet the definition of a "sign" since this requires objective independent verification, therefore at best the concept is a misnomer and at worst it is an intentional prevarication with an implied subtext of mandatory opiate treatment for anyone complaining of pain. So let’s look at some of the descriptor adjectives that help assess pain and are absolutely necessary as part of that description.

LOCATION

While it is obvious that the location of pain should be specified, many physicians assume the location of pain is static, and fail to recognize any new pain locations on subsequent office visits. Given a patient's limited understanding of anatomy and their erroneous interpretation of commonly used anatomical terms, it is prudent to not use descriptor adjectives alone in defining the location of pain. Pain maps or pain drawings may be useful in defining pain location in the commonly understood term between the physician and the patient. The anatomical term "hip" has various interpretations by patients from the top of the iliac crest to the inferior gluteal area to the lateral thigh to the inner groin and to the midline low back. Simply marking the location on an anatomical diagram is far more rapid and reduces the patient miscommunication.

Descriptions of relative intensities, radiation locations, and pain character can also be encoded in these diagrams. The usefulness of pain diagrams is compromised when patients have complaints of multiple pain locations simultaneously that are widespread, and are unable to focus on one or two locations of maximum pain intensity. Of course, there are widespread pain diagnoses that should be entertained when the patient so encodes the pain diagram. Pain patterns such as neuropathic pain are frequently identified using this type of diagram in addition to patients with global pain that will respond poorly to injection or interventional pain therapies.

INTENSITY

Perceived intensity is by far the most commonly used and misused measure of pain. What we ask the patients to do in rapidly defining a scalar distillation of a complex multidimensional array of continually and rapidly changing parameters is an impossible task. Frequently patients hesitate and are obviously confused regarding this request since the number generated on follow-up visits in those with dynamic pain varies widely from hour to hour or minute by minute, and vary with emotional state and current stress level.

Therefore asking patients to rate their pain intensity demands explanation by the physician on exactly what is meant. Frequently, patients lack the memory of what the perceived intensity was the day before, much less comparing it last month's pain with an ill defined scale of 1-10 or 1-100. Patients frequently are perfunctory about rating the intensity of the pain due to lack of specific explanation of this value as an instantaneous pain, average over the month (impossible for them to calculate or accurately estimate), peak, median, mode, or range. Some patients with high stress level or those suffering from weather related arthritic pain exacerbations will automatically rate their pain much higher as will those with secondary gain issues. Patients that consistently rate their pain at a 10 despite the use of interventions or medications they claim are helping definitely need evaluation for secondary gain or somatization disorders. Pain rated above the end of the defined scale suggest the patient feels they cannot communicate to the physician the extreme degree of pain with which they suffer resulting in amplification into the absurd.

Physicians typically view pain scales to help them document improvement in therapies but there is very little evidence that pain is perceived in a linear fashion by patients. Other sensory perception systems in the body, including hearing, frequently function over an extremely wide range with several orders of magnitude. Perception of varying degrees of neural activity in the systems is better characterized utilizing a logarithmic scale rather than a linear scale. If pain perception is indeed a logarithmic function, then the numeric scale values obtained via querying patients regarding their pain intensity cannot be added, averaged, nor can any assertions be made regarding pain reduction degree when measuring interventions to reduce pain. This can be seen in the following chart that illustrates the potential non-linearity and phase shifts that occur when plotting stimulus vs perceived VAS in different patient populations. The hypersensitive population (chronic pain NMDA receptor activation, opiate induced hyperalgesia, somatization disorders, moderate to severe anxiety or depression, sleep disturbance, etc) have a phase shift of the stimulus curve from the normal, and perceive far more pain at a lower stimulus level. They are unable to differentiate moderate from severe levels of perceived pain and amplify the VAS across the board. The opposite of the hypersensitive are the stoic or those trained to not react to pain. The World War II veterans frequently have little complaint of pain even during severely painful stimuli. Some major implications of the diversity of pain perception in different populations are:

It is not possible to average pain numbers across different populations. The pain perceived by one population for the same stimulus is not reflected in other populations. VAS scales may not be used within a given population or an individual to predict statistical or actual success of an intervention designed to reduce pain.

Asynchronous Pain Perception vs Stimulus Intensity

For instance, in the hypersensitive chronic pain population, a reduction in stimulus intensity of 50% by a given intervention (from 100 to 50) results in only a 1.5 point reduction in VAS [3]. Therefore, pain injections or opiates that significantly reduce nociception may only marginally reduce pain perception. The hyperbolic function of pain vs improvement has been studied using synthetic modeling compared to hip replacement surgery patients and it was found to be futile to determine pain improvement as a percentage so the most accurate assessment of pain intensity is not yet known [2] Another study (graphically displayed below) of VAS measured in normal and fibromyalgia (FMS) patients given pulses of painful heat at different temperatures revealed similar findings of non-linear pain perception in the hypersensitive FMS patients with approximately double the pain perception in FMS patients compared to normal patients [4]. Therefore production of pain and reduction of pain cannot be averaged due to non-linearity of the FMS data, and VAS scores from different populations cannot averaged together or arithmetically manipulated otherwise.

The most commonly employed pain scale is that of the verbal rating scale (VRS) pain perception on a scale of 0 to 10. It lacks any written patient derived assessment, takes little time, and may be encoded into the chart directly. The VAS or visual analogue scale requires the patient to physical mark or indicate on a printed scale, has a higher incomplete rate, and demonstrates no advantage over the VRS in a study [5].

No Pain_____________________________________________Worst Possible Pain

This VRS and VAS are commonly employed in hospitals, ASCs, and physician offices as a well accepted means of quantifying pain intensity perception, however if it is only used during follow-up office visits as a single number, the usefulness is highly questionable. The National Institutes of Health (NIH) use a numeric scale but also ask questions that bring a more reasonable albeit imperfect assessment.

The NIH asks the following questions regarding the 11 point Numeric Scale:

The patient is asked anyone of the following questions: What number would you give your pain right now? What number on a 0 to 10 scale would you give your pain when it is the worst that it gets and when it is the best that it gets? At what number is the pain at an acceptable level for you? When the explanation suggested in #1 above is not sufficient for the patient, it is sometimes helpful to further explain or conceptualize the Numeric Rating Scale in the following manner:

0= No Pain

1-3 = Mild Pain (nagging, annoying, interfering little with ADLs)

4-6 = Moderate Pain (interferes significantly with ADLs)

7-10 = Severe Pain (disabling; unable to perform ADLs)

Attempting to couple the scale directly to function or behavior is tempting and has been published previously by Hochman [6] but there are always shortcomings to directly linking function/pain because this may not be a linear link [7] nor assess the actual degree of physical activity outside the ADLs. However, the Hochman scale is a definite improvement over the VAS in chronic pain patient populations. The Hochman scale is as follows:

0 No pain

1 Occasional pain effectively managed by Aspirin, Tylenol, Ibuprofen, one tablet, three times a day or less - or by opioids with no limitations on activities of daily living

2 Frequent pain, managed only by 1 or more tablets of ASA, acetaminophen, ibuprofen, every four hours - or by opioids with slight impairments of activities of daily living

3 Frequent pain, not effectively managed by NSAIDs, requiring an opioid medication, with mild restrictions on activities of daily living

4 Frequent pain, moderately affecting activities of daily living, but still controlled by opioid medications

5 Frequent or almost constant pain. Contained by opioids, but still causing significant limitations on activities of daily living and occasionally causing the patient to be house or bed confined

6 Constant pain, moderately contained by opioids, but with frequent limitations of activities of daily living. Frequently causes confinement to bed or the house.

7 Constant pain. only partially contained by opioids at the doses prescribed. with continuous limitation of activities of daily living

8 Constant pain, frequently disabling, making most activities of daily living difficult if at all possible

9 Constant pain, uncontained by prescribed medications and doses, completely disabling of activities of daily living, requiring interventions or assistance by others, preventing any form of employment and fully qualifying the patient for Social Security Disability

10 Intolerable pain requiring emergency room treatment, generally with opioid injections

Jack Harich of the International Pudendal Neuropathy Association has published the following scale that may be useful to correlate behavior with a numeric assessment of pain intensity, thereby reducing histrionic responses or symptom amplification in pain scales lacking symptom correlation.

Comparative Pain Scale



Other Scales:

The Wong-Baker Faces Scale is useful in children's pain assessment but is rarely used in adult pain assessment, with the exception of the older adult.



Five Point Graphic Rating Scale is remarked as non-specific and not sensitive producing inconsistent feedback



Six-point Numeric Rating Scale (NRS 0-5) (Morrison et al., 1998)

Eleven-point Numeric Rating Scale (NRS 0-10) (Bergh et al., 2000, 2001; Closs et al., 2004; Gagliese et al., 2005; Kaasalainen & Crook, 2004; VHA/DoD, 2002)



Twenty-one point Numeric Rating Scale (NRS 0-20) (Chibnall & Tait, 2001; Herr et al., 2004; Taylor & Herr, 2003)

Verbal Descriptor Scale (VDS) appears to be easiest and most preferred by older adults and easiest for those with cognitive impairment (Bergh et aI., 2000, 2001; Closs et al., 2004; Gagliese & Katz, 2003; Herr et al., 2004; Manz et al., 2000; Taylor & Herr, 2003)

Four-point Verbal Rating Scale (VRS) (Closs et al., 2004)

Pain Thermometer (PT) (Herr & Mobily, 1993; Taylor & Herr, 2003)



Present Pain Inventory Scale (PPI) (Gagliese & Katz, 2003; Gagliese et al., 2005; Kaasalainen & Crook, 2004; Melzack & Katz, 1992; Pautex et al., 2005)

Seven-point Graphic Rating Scale (GRS) (Bergh et al., 2000, 2001)

IMPROVED PAIN ASSESSMENT WITH DESCRIPTORS

Adding further information regarding pain can help delineate new pain patterns, recognize potentially dangerous pain sources, and develop an understanding of contributing factors to pain. The McGill Questionnaire and later, the McGill Short Form (SF-MPQ) were developed to aid in this endeavor. The latter consists of 11 subjective and 4 affective questions in addition to a pain map and a VAS scale. The first 11 questions are the sensory or physical component of the test while the latter 4 questions are the affective (emotional) component of the test. Each question has 4 scores: 0 (not marked), mild=l, moderate=2, and severe=3 points for a highest possible score of 45. Sensory scores above 25 are termed severe, 16-25 are moderate, and 6-15 are mild. Affective total scores of >8 indicates a strong emotional component to the pain.

In a study of patients with chronic low back pain, there was a very strong test-retest coefficient for the pain rating index [8]. Patients with Minnesota Multiphasic Personality Inventory (MMPI) profiles of depression and hysteria were found to have high affective and pain intensity scores on the SF-MPQ (short form). Hypochondriasis on the MMPI gives high scores on the SF-MPQ in all scales. A pure affective score elevation suggests emotional disturbance separate from pain [9]. In patients undergoing surgical disc decompression for radiculopathy, SF-MPQ preop values of 17 or more sensory or 7 or more affective reduced acceptable outcome to less than 50% rate [10]. The sensory, affective, and total scores of the MPQ and SF-MPQ were found to be significantly correlated [11] which is important because the SF-MPQ requires 2-3 minutes to complete while the MPQ requires 10-15 minutes (not practical for repeat office visit assessments). A comparison of MPQ scores for acute pain and chronic pain revealed that patients with acute pain displayed a greater use of sensory word groups while chronic pain patients used affective and evaluative groups with greater frequency [11]. The shortcomings of the SF-MPQ include the lack of temporally related pain information, inadequate function and sleep disturbance assessment, and lack of use of ranges of pain intensity. The McGill Short Form Pain Questionnaire is shown below along with typical values seen (total score) for various types of pain.

The brief pain inventory (BPI) is an excellent tool to follow chronic pain patients receiving long term treatment with medications or interventions. The survey takes 5 min or less to fill out and assesses emotion and functionality in addition to pain intensity. BPI provides information on the intensity of pain (the sensory dimension) as well as the degree to which pain interferes with function (the reactive dimension). The BPI also asks questions about pain relief, pain qua1ity, and the patient's perception of the cause of pain. The tool incorporates a 0 to 10 numeric rating scales (NRS) for each item rating. The BPI asks patients to rate their pain at the time of responding to the questionnaire (pain now), and also at its worst, least, and average over the previous week due to the variability of pain. While it is necessary to 1imit the dimensions of assessment, it is critical to estimate the degree to which pain limits patient function. Interference of function can be thought of as a reactive dimension. An effective intervention for pain control should demonstrate its effectiveness on more than a reduction in pain intensity alone. Again, using numeric 0 to 10 scales, with 0 being "no interference" and 10 being "interferes completely," the BPI asks for ratings of the degree to which pain interferes with mood, walking and other physical activity, work, social activity, relations with others, and sleep. The mean of these scores can be used as a pain interference score. The BPI has demonstrated respectable test-retest item correlations (reliability), at least over short intervals. Evidence for the validity of the BPI comes from multiple studies of patients with different types of pain. Metastasis vs none produced expected differences in pain severity. Ratings of pain interference with various activities increased as ratings of pain severity were higher. The proportion of patients receiving opioid analgesics increased with increased severity rating. Finally, the correlations among the items differed in a logical way from one disease to another, suggesting that the BPI is sensitive to differences in pain characteristics associated with different diseases. A unique feature of the BPI is that it has been validated in many languages with similar results regardless of geographical location or culture. It has been shown the BPI rates cancer patient functional deficits greater than that of non-cancer chronic pain patients, however vice versa is true with emotional disturbances due to pain [12]. The BPI should be considered as a means of measurement of these multiple values within one simple instrument. There is no scoring algorithm, but "worst pain" or the arithmetic mean of the 4 severity items can be used as measures of pain severity and the arithmetic mean of the 7 interference items can be used a as a measure of pain interference. The quality of life measures in this type of scale can be useful in tracking over time. However chronic pain patients typically have more emotional disturbances, poorer function, and lower quality of life than patients with virtually any other chronic disease.

OTHER PAIN ASSESSMENT TOOLS

The P3 (Pain Patient Profile) pain assessment is a tool with 44 questions requiring approximately 15 minutes to complete: it’s too long for routine follow-up visits, but may be reasonable for an initial pain assessment. The tool is a Pearson assessment tool (fee based) with chronic pain normalized scales for somatization, depression, anxiety, and a validity scale. The average values in a chronic pain population were 28 (sd 6),27 (sd 7),23 (sd 6) using the Tollison and Langley data 1995. The SF36 is a standardized test question set that are readily available without paying a fee, however scoring the test requires a computer program since the questions are weighted. Therefore, one would pay a scoring fee for each test, making it impractical for routine office follow-up visits; although for initial screening the test may be useful. It contains the following subscales: Physical function, Role Physical, Bodily Pain, General Health, Mental Health, Role Emotional, Social Function, and Vitality. It is not a useful evaluation alone in the absence of other measures such as pain maps, but is validated and has a long history of use in pain measurement.

ASSOCIATED CONDITION MEASUREMENT

The Zung anxiety assessment is a useful tool when patients insist on being placed on benzodiazepines and an objective measurement of improvement is needed in order to continue such therapy.

The Roland Morris and Oswestry tests are useful for functional assessment.

All these tests may be found at: http://algosresearch.org/PracticeTools/PracticeTools.html.