Defining pain

The International Association for the Study of Pain (IASP) defines pain as “an unpleasant sensory and emotional experience associated with actual or potential tissue damage or described in such terms as damage.” The primary purpose of pain is to protect the body. It occurs whenever there is tissue damage, and it causes the individual to react to remove the painful stimulus. Pain is also a sensation with more than one dimension. To the individual, pain is both an objective and a subjective experience. The objective dimension is the physiological tissue damage causing the pain. The subjective dimensions include the following :

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  A perceptual component: the patient’s awareness of the location, quality, intensity, and duration of the pain stimulus

  
  
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  An affective component: the psychological factors surrounding the patient’s pain experience, including the patient’s personality and emotional state

  
  
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  A cognitive component: what the patient knows and believes about the pain resulting from his or her cultural background and past pain experiences (both personal pain experiences and those of others)

  
  
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  A behavioral component: how the patient expresses the pain to others through communication and behavior

All these components taken together constitute the patient’s pain experience. Thus all must be addressed for a successful pain management program. When the subjective components of the pain experience are ignored, it is entirely possible that the patient’s underlying tissue damage may be corrected without her or his pain perception being cured.

In addition, recognizing that pain is more than simply a physical injury or disease process helps clinicians explain some of the inconsistencies observed in patients with chronic pain. Why is a patient’s pain report out of proportion to the magnitude and duration of the injury? Why is pain intolerable to one person and merely uncomfortable to another? And why is pain tolerable in one instance but overwhelming to the same individual when experienced at a different time?

The answers lie in the interconnectedness of the nervous system and the fact that pain transmission involves several higher centers. To select the most appropriate intervention, it is important for clinicians to have at least a general idea of the pain pathways. An overview of pain anatomy and physiology is discussed next.

Pain anatomy

Pain arises from the stimulation of specialized peripheral free nerve endings called nociceptors. Injurious stimulation to the skin, muscle, joint, viscera, or tissue can trigger these peripheral terminals, whose cell bodies are in the dorsal root ganglia and trigeminal ganglia. The density of nociceptors varies between as well as within these tissues. Nociceptors are extremely heterogeneous, differing in the neurotransmitters they contain, the receptors and ion channels they express, their speed of conduction, their response properties to noxious stimuli, and their capacity to be sensitized during inflammation, injury, and disease.

Nociceptors found in interstitial tissues become excited with extreme mechanical, thermal, and chemical stimulation, whereas nociceptors found in vessel walls become excited with these stimuli plus marked constriction and dilation of the vessels. These receptors respond directly to some noxious stimuli and indirectly to others by means of one or more chemicals (histamine, potassium, bradykinin) released from cells in the traumatized tissues.

Thermal nociceptors are triggered by intense hot or cold temperatures (>45°C or <5°C). They have fibers that are of small diameter and thinly myelinated with moderately fast conduction signals of 5 to 30 m/s. Mechanical nociceptors are triggered by intense pressures applied to the skin, such as a pinch. They also have thinly myelinated, moderately conducting fibers with speeds of 5 to 30 m/s.

Polymodal nociceptors are triggered by more than one sensory modality (mechanical, chemical, or thermal). These nociceptors have small-diameter, nonmyelinated fibers that conduct more slowly, generally at velocities less than 1.0 m/s (see Table 30.1 ). Stimulation of these receptors causes sensations of diffuse burning or aching pain. The difference in the fibers’ size and myelination determines the speed at which impulses will travel to the brain.

These three types of nociceptors are broadly distributed in the skin and tissues and may work together. One example would be hitting one’s shin against a table: a sharp “first pain” is felt immediately, followed later by a more prolonged aching, sometimes burning, “second pain.” The fast, sharp pain is transmitted by A delta fibers that carry information from thermal and mechanical nociceptors. The slow, dull pain is transmitted by C fibers that are activated by polymodal nociceptors.

Nociceptive input travels on A delta and C fibers into the dorsal horn of the spinal cord, where the gray matter is laminated and organized by cytological features. The first-order A delta and C fibers synapse with second-order neurons in lamina I (marginal layer), II (the substantia gelatinosa [SG]), and V. The second-order neurons do one of three things. A small number synapse with motor neurons, causing reflex movements (e.g., withdrawing the hand from a hot object). Others synapse with autonomic fibers, causing responses such as changes in heart rate and blood pressure and localized vasodilation, piloerection, and sweating. Most, however, travel a multisynaptic route to the higher centers by means of the ascending tracts. ^,

There are four major classes of neurons responding to pain in the dorsal horn: low-threshold nociceptive-specific neurons designated class I; wide dynamic range (WDR) neurons designated class II; high-threshold nociceptive neurons designated class III; and a fourth, non-responder group of neurons that develop spontaneous activity with exposure to endogenous inflammatory cytokines, designated class IV. Nociceptive-specific neurons are most abundant in superficial lamina; their receptor fields are discrete and vary from one to several square centimeters. WDR neurons, in contrast, respond to a wide range of stimuli from A delta, A beta, and C fibers in a graded manner (i.e., the rate of firing escalates with increasing intensity of stimulation), can be found in all lamina, and are the most prevalent cells in the dorsal horn. Because of their unique response to innocuous or nociceptive input, as well as their larger receptor field, WDR neurons play an important role in the central sensitization and the plasticity of the spinal cord.

Nociceptive input crosses at the cord level to the anterolateral quadrant of the ascending contralateral spinothalamic tract ( Fig. 30.1 ). The axons of the anterolateral quadrant are arranged so that the sacral segments are most lateral, with the lumbar segments more medial and the cervical segments most central. This arrangement may be important clinically in that symptoms may be provoked according to dermatomal maps to some degree. Pain dermatomes overlap to several adjacent dorsal roots, so boundaries can be less distinct, requiring the clinician to distinguish the pain and dysfunction.

Pain Pathway.

(From Gould BE. Pathophysiology for the Health Professions . 2nd ed. Philadelphia: WB Saunders; 2002.)

The anterolateral tract is divided into three ascending pathways: the spinothalamic, spinoreticular, and spinomesencephalic. The spinothalamic tract conveys information about painful and thermal stimulation (location and intensity) directly to the ventral posterior lateral nucleus of the thalamus, as well as sending collaterals off at the brain stem to join the spinoreticular tract. Axons within the spinoreticular tract synapse on neurons of the reticular formation of the medulla and pons, which relay information to the intralaminar and posterior nuclei of the thalamus and to other structures in the diencephalon, such as the hypothalamus (emotional response to pain).

Axons in the spinomesencephalic tract relay information to the mesencephalic reticular formation and periaqueductal gray matter by way of the spinoparabrachial tract. It then projects to the limbic system, which is involved with the affective component of pain (central modulation of pain).

The thalamus processes and relays information to several higher centers. Each projection serves a specific purpose. Axons of the spinothalamic tract project information to both the lateral and medial nuclear groups of the thalamus. The lateral nuclear group of the thalamus is where information about the location of an injury is thought to be mediated. Injury to the spinothalamic tract and the lateral nuclear group of the thalamus causes central neuropathic pain, which is discussed in further detail later.

Projections from the spinoreticular tract to the medial nuclear group of the thalamus are concerned with processing information about nociception, and they also activate nonspecific arousal systems. These pathways project from the thalamus to the basal ganglia and many cortical areas.

Projections to the postcentral gyrus (sensory cortex) are responsible for pain perception. It is from this projection that pain can be localized and characterized. Projections from the thalamus to the frontal lobes and limbic system are concerned with pain interpretation. It is from all these projections that an individual perceives pain as hurting. Projections from the thalamus, as well as from the limbic system and sensory cortical areas, to the temporal lobes are responsible for pain memory; and projections from the thalamus to the hypothalamus are responsible for the autonomic response to pain.

Pain transmission

Ascending transmission of pain impulses is mediated by the action of the chemical excitatory neurotransmitter glutamate (A delta and C fibers) and tachykinins such as substance P (C fibers). Glutamate and neuropeptides have distinct actions on postsynaptic neurons, but they act together to regulate the firing properties postsynaptically. Tachykinins’ activity is thought to prolong the action of glutamate, as levels are increased in persistent pain conditions. The substrates of nociception that exist at the spinal level are complex in that more than 30 different neurotransmitters acting on more than 50 different receptors have been identified in the spinal cord and associated with some pain-related phenomenon. Modulation of these substrates will assist in the effectiveness of therapeutic interventions and will be discussed next.

Pain modulation

Nociceptive transmission is modulated at several points along the neural pathway by both ascending and descending systems.

The gate control theory

The SG contains an ascending gating mechanism to block nociceptive impulses from leaving the dorsal horn of the spinal cord. The first-order neurons for both nociceptive and non-nociceptive information synapse with second-order neurons in the SG. The second-order neurons for both types of information project to specialized neurons named T-cells (transmission cells) in lamina V. For pain transmission to occur, T-cells must be stimulated while the SG is inhibited. The input from A delta and C fibers stimulates the T-cells and inhibits the SG ( Fig. 30.2 ). Therefore A delta and C fiber input opens the gate, allowing pain transmission to the higher centers. On the other hand, when the SG and T-cells are both stimulated, the T-cells are inhibited, and the gate is closed to pain transmission. The input from non-nociceptive A beta fibers carrying information from pressoreceptors and mechanoreceptors stimulates both the T-cells and the SG. Therefore A beta fiber input closes the gate, blocking pain transmission.

Schematic Representation of Spinal Structures Involved in the Gate Control Theory of Pain Transmission.

Afferent input by means of both large- and small-diameter fibers is theorized to influence the transmission cell (T) directly and through small internuncial neurons located within the substantia gelatinosa (SG).

(From Nolan MF. Anatomic and physiologic organization of neural structures involved in pain transmission, modulation, and perception. In: Echternach JL, ed. Pain. New York: Churchill Livingstone.)

One example that illustrates the gate control theory is the use of transcutaneous electrical nerve stimulation (TENS) in an area that overlaps the injury. It works to reduce pain by activation of large-diameter A beta fibers that “closes the gate,” thereby preventing pain transmission to the higher centers of the brain. This is also why shaking (vibrating) your hand after hitting your thumb with a hammer temporarily relieves pain.

Categorizing pain

Pain is grouped into several categories: acute, chronic, referred, central neuropathic, autonomic, and peripheral.

Acute pain is the normal predicted physiological response and serves as a warning. It alerts the individual that tissues are exposed to damaging or potentially damaging noxious stimuli. Acute pain is localized, occurs in proportion to the intensity of the stimuli, and lasts only as long as the stimuli or the tissue damage exists (1 to 6 months). Although acute pain is associated with anxiety and increased autonomic activity (increased muscle tone, heart rate, and blood pressure), it is usually relieved by interventions directed at correcting the injury. The pain experience is usually limited to the individual.

Chronic pain is usually referred to as intractable pain if it persists for 6 or more months. It is defined as pain that continues after the stimulus has been removed or the tissue damage heals. Physiologically, chronic pain is believed to result from hypersensitization of the pain receptors and enlargement of the receptor field in response to the localized inflammation that follows tissue damage. Chronic pain is poorly localized, has an ill-defined time of onset, and is strongly associated with the subjective components outlined previously. It does not respond well to interventions directed solely at correcting the injury. Chronic pain patients frequently report other symptoms, such as depression, difficulty sleeping, poor mental and physical function, and fatigue. The effects of the pain experience extend beyond the individual and affect the family, the workplace, and the social sphere of the individual.

Referred pain is felt at a point other than its origin. Pain can be referred from an internal organ, a joint, a trigger point, or a peripheral nerve to a remote musculoskeletal structure. Referred pain usually follows a specific pattern. For example, cardiac pain is frequently referred to the left arm or jaw; the referral pattern for trigger points is exact enough to be used as a diagnostic tool and is often used by physicians to diagnose pathology. Referred pain is the result of a convergence of the primary afferent neurons from deep structures and muscles to secondary neurons that also have a cutaneous receptive field. ^,

Although it is now recognized that all neuropathic pain results in abnormal activity within the CNS, pain initiated or caused by a primary lesion or dysfunction of the CNS is referred to as central neuropathic pain. The involvement of the nervous system can be at many levels: nerves, nerve roots, and central pain pathways in the spinal cord and brain. In this circumstance, there is permanent damage to the nervous system (usually a peripheral nerve) and likely anatomical reorganization of spinal terminations of surviving axons or ectopic activity from a neuroma that contributes paroxysmal, persistent input to the spinal cord. In addition to anatomical reorganization in the spinal cord, there could be some reorganization in the rostroventral medulla (RVM) as well, but more likely there is prolonged input to the RVM that sustains facilitatory influences that descend to the spinal cord. Less appreciated, descending facilitatory influences on spinal sensory processing could also be important to maintenance of chronic pain conditions, particularly those that persist in the absence of obvious tissue pathology.

Central neuropathic pain is medically diagnosed by its defining neurological signs and symptoms; it is verified with neuroimaging tests that identify a CNS lesion and rule out other causes. It is important that the therapist be able to localize the level and differentiate between central and peripheral pain. Central neuropathic pain can be caused by vascular insult; traumatic, neoplastic, and demyelinating diseases; and surgery (including vascular compromise during surgery). Central neuropathic pain is distinct from nociceptive pain (nonneuronal tissue damage).

The onset of central neuropathic pain is usually delayed after the occurrence of the initial episode that results in damage to the CNS; onset of pain may occur during the phase of recovery from neurological deficits. Pain originating from a cerebrovascular incident and spinal cord injury usually begins weeks or months after the insult, whereas pain originating from tumors may take years to begin.

Individuals with central neuropathic pain may have difficulty describing their pain and report burning, aching, pricking, squeezing, or cutting pain after cutaneous stimulation, movement, heat, cold, or vibration. A normally non-noxious stimulus, such as moving clothing across skin, becomes agonizing. In some cases, pain begins spontaneously. Pain intensity varies, but it does seem to be associated to some degree with the location of the lesion. Allodynia (pain from normally non-noxious stimuli) and dysesthesia are common, and one of the characteristic features of central neuropathic pain is that the clinical symptoms persist long after the stimulus has been removed.

Central neuropathic pain is topographical. The site of the lesion determines the location of the symptoms. The pain may involve half the body, an entire extremity, or a small portion of one extremity. It is frequently migratory. Thalamic pain is the classic example of central neuropathic pain.

Central neuropathic pain is difficult to treat. Surgery is not helpful for most individuals with central neuropathic pain, and medications have not been effective in permanently relieving the symptoms. Therefore the treatment of patients with central neuropathic pain stresses coping strategies and prevention of loss of activity and participation. The ideal management of a chronic pain patient is by a multidisciplinary approach, including disciplines such as internal medicine, neurology, anesthesia, nursing, psychology, pharmacy, rehabilitation medicine, physical therapy, occupational therapy, and others. The limitation of this approach is that access to such a wide range of specialists is often available only at large medical centers and special pain clinics, which restricts access to a limited number of patients.

Under normal conditions there is a fine balance between the parasympathetic and sympathetic branches of the autonomic nervous system (ANS). Parasympathetic activity maintains homeostasis, whereas sympathetic activity functions to make “fight-or-flight” changes in response to stress. Stimulation of the autonomic efferent fibers is not normally painful. However, the balance between afferent input and the descending sympathetic nervous system (SNS) is disrupted when there is injury, resulting in exaggerated and prolonged sympathetic activity, allodynia, and hyperalgesia (increased response to normally painful stimuli)—hence, autonomic pain.

Allodynia is a product of the phenomenon of central sensitization. After injury, new axons sprout from the sympathetic efferent neurons. These fire spontaneously and, because they synapse on the cell bodies of the primary afferent neurons, cause them to fire as well. In addition, the dorsal horn neurons themselves become more excitable. They show an enlargement in their receptive field and become more sensitive to mechanical, thermal, and chemical stimulation. The result is an increase in the neuronal barrage into the CNS and the perception of pain with usually nonpainful stimuli.

Complex regional pain syndrome (CRPS) is an example of pain that arises from abnormal activity within the ANS. CRPS has been classified into two distinct types : CRPS type I (formerly reflex sympathetic dystrophy ) follows mild trauma without nerve injury, and CRPS type II (formerly causalgia ) follows trauma with nerve injury. CRPS type I generally begins within the month after the injury, whereas CRPS type II can occur any time after the injury.

The main features of CRPS type I are constant burning pain that fluctuates in intensity and increases with movement, constant stimulation, or stress. There are also allodynia and hyperalgesia, edema, abnormal sweating, abnormal blood flow and trophic changes in the area of pain, and impaired motor function. CRPS type I is relieved by blocking the SNS, indicating that the pain is sympathetically maintained.

CRPS type II occurs in the region of a limb innervated by an injured nerve. The nerves most commonly involved in CRPS type II are the median, sciatic, tibial, and ulnar; involvement of the radial nerve is rare. Pain is described as spontaneous, constant, and burning and is exacerbated by light touch, stress, temperature change, movement, visual and auditory stimuli, and emotional disturbances. Allodynia and hyperalgesia are common and may involve the distribution of more than one peripheral nerve. As with CRPS type I, edema, abnormal sweating, abnormal blood flow, trophic changes, and impaired motor function occur. The symptoms spread proximally and can involve other areas of the body. Evidence also points to sympathetic involvement in CRPS type II.

The treatment of CRPS is complex and must be carefully coordinated among members of an interdisciplinary team including the neurologist (medications), psychologist (behavior), anesthesiologist (injections), and therapist (functional recovery). The therapist provides the core treatment to improve function. Therapists need to pay close attention to the following aspects of the disorder: (1) the degree of motor abnormalities, including restricted active range of motion (ROM), abnormal posturing, spasm, tremor, and dystonia; (2) true passive range restriction; (3) hyperesthesia and allodynia; (4) swelling and vasomotor changes; and (5) evidence of osteoporosis by radiograph. Please refer to Case Study 30.1 for interventions for patients with CRPS.

Peripheral pain results from noxious irritation of the nociceptors. The character of peripheral pain depends on the location and intensity of the noxious stimulation, as well as which fibers carry the information into the dorsal gray matter. As noted previously, information carried on A delta fibers is sharp and well localized, begins rapidly, and lasts only if the stimulus is present, whereas information carried on C fibers is dull and diffuse, has a delayed onset, and lasts longer than the duration of the stimulus. The treatment of peripheral pain is covered in detail in Chapter 16 .

The management of central versus peripheral pain is determined by the type of pain—acute or chronic—and the clinical features present, including clinical localization; time of onset; laboratory study localization; response to analgesics, including narcotics; response to antidepressants; and response to nerve block or neurectomy. Differentiation among features will drive the treatment plan, but because some peripheral and central forms can coexist, diagnosis may be difficult.

The multidimensional aspects of chronic pain make it important to evaluate the causes as well as the emotional and cognitive sequelae. Persistent pain is now considered to have a psychogenic component. The longer an individual has pain, the more a psychological component may become dominant. Many emotional factors can strongly influence pain, such as pain thresholds, past experiences with pain, coping styles, and social roles. The emotional experience that we perceive with pain reflects the interaction of higher brain centers and subcortical regions, such as the amygdala and cingulate gyrus (limbic system). Positron emission tomography of patients with chronic neuropathic pain demonstrates a shift of acute pain activity in the sensory cortex to regions such as the anterior cingulate gyrus. Understanding the physical limitations imposed by chronic pain is an area that therapists commonly assess; it is the mind-body connection that is often less articulated by the patient and more difficult for the practitioner.

Treatment of chronic pain should include a patient-centered approach, given the unique manifestations that occur in an individual’s response to pain. Patient-centered models, such as the biopsychosocial and ICF model, provide a framework that embraces a multidisciplinary team approach practiced in pain clinics. In such models, chronic pain has been noted to include psychological factors such as feelings of fear, anxiety, and depression, which are known to have the ability to modulate and exacerbate the physical pain experience. For example, a patient with chronic pain who has the fear that movement will increase pain may alter his activity, causing muscular shortening, spasms, and a spiraling course of more pain and disability. The focus in treating patients with chronic pain should be on improving functional physical activity, decreasing peripheral nociception and central facilitation, and providing cognitive and behavioral strategies to help in resuming normal activities.

Examination of the patient with pain

The examination of a patient with pain can be challenging because the therapist must frequently weed through the individual’s emotions, behaviors, and secondary gains to identify the source of the symptoms. Many patients are not referred to therapy until they have participated in weeks, months, or even years of failed interventions, and their expectations and patience are at low levels. They often approach therapy anticipating more instructions, more frustration, and more pain. Despite these obstacles, therapists must strive to complete pain evaluations that include evidence-based measurable, reproducible information that identifies the source of pain and provides direction toward treatment that is both beneficial and cost-effective and that assists in establishing attainable goals. The time allotted for the examination may be dependent on the type of practice setting; many therapists send a comprehensive questionnaire to the patient or ask the patient to arrive early to complete important paperwork. It is essential to develop a trusting relationship, ensuring that the patient feels that the therapist has listened to his or her concerns and has acknowledged his or her fears, and will participate in a plan for improving his or her physical, mental, and functional abilities.

Pain outcome measurement

Outcome measures have become well established in pain research. Because of the variability in outcome measures across clinical trials hinders evaluation of efficacy and effectiveness of treatments, the Initiative on Methods, Measurement, and Pain Assessment in Clinical Trials (IMMPACT) has recommended that six core outcome domains should be considered when designing chronic pain clinical trials. These six core outcome domains were (1) pain; (2) physical functioning; (3) emotional functioning; (4) participant ratings of improvement and satisfaction with treatment; (5) symptoms and adverse events; and (6) participant disposition (e.g., adherence to the treatment regimen and reasons for premature withdrawal from the trial). These domains can assist in determination of outcome measures appropriate in clinical practice. Pain measurement tools are designed to provide information about the intensity, location, physical function, and character of a patient’s symptoms at the time of the evaluation. This information can then be merged with the pain history, the disease or pathology history, and the physical findings to identify the cause of the pain. The disease or pathology management and its pain measurement will be the responsibility of the physician, whereas the movement limitations caused by the pain are the responsibility of the therapist. A number of pain measurement tools are available. These tools are used by professionals whose focus is pathology, as well as professionals whose responsibility is helping the patient to regain functional activities and life participation. The applications and limitations of several are discussed.

Patient reported outcomes have been utilized in the treatment of pain. The National Institute of Health funds the Patient-Reported Outcomes Measurement Information System (PROMIS), which provides psychometrically sound and validated patient-reported outcome measures free of charge that can be used in a wide range of chronic conditions. PROMIS is comprised of calibrated item banks to measure diverse health concepts such as pain, physical function, and depression; these are presented for each domain as individual items and/or instruments of various lengths. In addition, PROMIS includes several collections of items, termed profiles, which measure multiple domains. For example, the PROMIS-29 profile assesses seven domains, each with four questions; depression, anxiety, physical function, pain interference, fatigue, sleep disturbance, and ability to participate in social roles and activities. There is also an additional numeric pain intensity 0 to 10 rating scale (NPRS).

Measuring pain intensity

Research has shown that pain memory does not provide an accurate measure of pain intensity.

Pain intensity rating tools are scales that have the patient rate the current level of pain by marking a continuum or assigning a numerical value to the pain intensity ( Fig. 30.3 ).

Rating Scales for Measuring Pain Intensity.

(A) Simple descriptive pain scale (SDPS). (B) Visual analog scale (VAS). (C) Pain estimate. (D) Faces pain scale.

(D Reprinted from Bieri D, Reeve DA, Champion GD, et al. The faces pain scale for the self-assessment of the severity of pain experienced by children: development, initial validation, and preliminary investigation for the ratio scale properties. Pain. 1990;41:139–150, with permission from Elsevier Science.)

Each of the first three tools described here has been found to be reliable over time when used to measure pain that is present at the time of the rating. In general, however, patients who are depressed or anxious tend to report higher levels of pain and patients who are not depressed or anxious tend to report lower levels of pain on all three of these scales.

Visual analog scale.

With the visual analog scale (VAS), the patient rates the pain on a continuum that begins with “no pain” and ends with “maximum pain tolerable.” This tool provides an infinite number of points between the extremes, making it sensitive to small changes in pain intensity. However, it has not been found reliable for individuals who have impaired abstract thinking skills and may be unable to translate their pain intensity into a corresponding point on a line.

Simple descriptive pain scale.

With a simple descriptive pain scale (SDPS), the patient rates the pain on a continuum that is subdivided using descriptors that gradually increase in intensity. Sample descriptors are “no pain,” “mild pain,” “moderate pain,” “severe pain,” and “maximum pain tolerable.” This tool is more useful than the VAS for patients with impaired abstract thinking because it is easier for them to identify with the pain descriptors than with the line found in the VAS. However, patients have been found to favor the points corresponding to each descriptor rather than points between, resulting in a less sensitive tool than the VAS.

Pain estimate.

With a pain estimate, the patient assigns a numerical rating to the pain, staying within defined limits (most commonly between 0 and 100, where 0 represents no pain and 100 represents maximum pain tolerable). Because it provides a numerical range of scores, this tool is valuable for statistical analysis purposes. However, whereas some patients find assigning a numerical rating to their pain intensity easy, patients with impaired abstract thinking may have difficulty similar to that encountered with the VAS.

Faces Pain Scale.

With the Faces Pain Scale, the patient selects one of seven schematic faces representing gradually increasing pain intensities. The scale begins with a face representing no pain and ends with a face representing the most pain possible. This tool is designed for use with young children who do not have the ability to use any of the three previous tools. The Faces Pain Scale has been found to be valid across cultural lines and to have a strong correlation with other pain measures. It is simple to use, does not require verbal skills, and requires little instruction. It has been used successfully with children as young as age 3 and with individuals who are limited in verbal expression.

Localizing pain symptoms

Pain drawings.

The patient is asked to draw his or her symptoms on a schematic of the human body using a provided list of symbols ( Fig. 30.4 ). The result is a diagram describing the nature and location of the patient’s pain, which can be compared with the patient’s verbal report. In addition to providing a database, the pain drawing has been found to be useful in identifying individuals who have a heavy psychological or emotional component to their pain, making it helpful also in identifying patients who would benefit from further psychological evaluation.

Pain Drawing for Describing the Nature and Location of a Patient’s Pain Symptoms.

(From Cameron MH, ed. Physical Agents in Rehabilitation. Philadelphia: WB Saunders; 1999.)

Describing pain quality

Mcgill Pain Questionnaire.

One of the most popular scales to rate pain quality is the McGill Pain Questionnaire (MPQ), which includes 20 categories of descriptive words covering the sensory (numbers 1 to 10), affective (numbers 11 to 15), and evaluative (number 16) properties of pain ( Fig. 30.5 ). Sensory properties are measured using temporal, thermal, spatial, and pressure descriptors. Affective properties are measured using fear, tension, and autonomic descriptors. Evaluative properties are measured using pain experience descriptors. Each word has a numerical value based on its position within its category.

The McGill Pain Questionnaire Used to Rate Pain Quality.

(Reprinted from Melzack R. The McGill Pain Questionnaire: major properties and scoring methods. Pain. 1975;1:277, with permission from Elsevier Science.)

The patient is instructed to “select the word in each category that best describes the pain you have now. If there is no word in the category that describes the pain, skip the category. If there is more than one word that describes the pain, select the word that best describes the pain.”

The MPQ can provide the following types of information :

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  A pain-rating index based on the sum of the values of all the words selected

  
  
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  A pain-rating index based on the sum of the values of all the words in a given category

  
  
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  The total number of words chosen

The MPQ has been studied extensively and found valid for adults with acute and chronic pain as well as for those with a variety of specific pathological states. It provides clues into the specific cause of pain because it describes the patient’s symptoms.

However, the MPQ does pose some disadvantages. It is time-consuming, requiring more time to complete than any of the previously described rating scales. Thus it is not appropriate for quick estimates of pain after treatment. Patients, especially children, are frequently unfamiliar with some of the descriptors and ask the evaluator to assist by defining words. However, reliability and validity of this test are based on examiner objectivity, and care must be taken to avoid the introduction of evaluator bias by helping the patient to select appropriate descriptors. This issue can be dealt with by telling the patient, “If you do not recognize a word, it probably does not apply to you.”

Pediatric verbal descriptor scale.

Because a child’s description of pain is limited by a smaller vocabulary, Wilkie and associates have developed a verbal descriptor scale specifically for use with children ( Table 30.2 ). Their list includes 56 words commonly used by children aged 8 to 17 to describe their pain experience. The word list is divided into the four categories found in the MPQ. The evaluators’ research has shown the list to be useful for children with a variety of diagnoses because it is relatively free of gender, ethnic, and developmental bias.

TABLE 30.2

Pediatric Verbal Descriptor Scale

Reprinted from Wilkie DJ, Holzemer WL, Tesler MD, et al. Measuring pain quality: validity and reliability of children’s and adolescents’ pain language. Pain . 1990;41:151–159, with permission from Elsevier Science.

Dimension	Word	Dimension	Word	Dimension	Word	Dimension	Word
A	Annoying Bad Horrible Miserable Terrible Uncomfortable	S	Biting Cutting Like a pin Like a sharp knife Pinlike Sharp Stabbing	S	Itching Like a scratch Like a sting Scratching Stinging	A	Crying Frightening Screaming Terrifying
E	Aching Hurting Like an ache Like a hurt Sore	S	Blistering Burning Hot	S	Shocking Shooting Splitting	A	Dizzy Sickening Suffocating
S	Beating Hitting Pounding Punching Throbbing	S	Cramping Crushing Like a pinch Pinching Pressure	S	Numb Stiff Swollen Tight	E	Never goes away Uncontrollable
A	Awful Deadly Dying Killing

 

A , Affective; E , evaluative; S , sensory.

Caregiver checklist.

Patients who are unable to communicate verbally because of neurological disabilities may be unable to use any of the just-described pain measurement scales. However, because of pain associated with their medical conditions, extensive and repeated surgery, and behavioral oddities that might limit pain expression, these individuals are at high risk for having their pain go unrecognized. McGrath and colleagues have attempted to develop and categorize a checklist of demonstrated pain behaviors identified by caregivers of severely handicapped individuals. Although their list did not pass validity criteria, the researchers propose that clinicians develop a patient-specific checklist that could be used to gauge changes in the patient’s pain from the information gained during the caregiver interview portion of the evaluation of nonverbal handicapped patients.

In addition to qualifying and quantifying the patient’s pain, pain measurement tools have an additional value. They can be used to identify inconsistencies between a patient’s pain report and the clinician’s objective findings. For example, a patient with normal objective findings would not be expected to give a high pain report or draw symptoms over the entire pain drawing. Conversely, a patient with a multitude of objective findings within the severe range would be expected to provide a high pain rating. In addition, as objective symptoms subside, it is expected that the patient will report a similar decline on the rating scales. Inconsistencies between the patient’s pain descriptions and the therapist’s findings should serve to alert the clinician that the patient might require cognitive or affective intervention in addition to physical treatment.