6 Assessment of Pain
The Massachusetts General Hospital Handbook of Pain Management
Assessment of Pain
Alyssa A. LeBel
When you can measure what you are speaking about, and express it in numbers, you know something about it; but when you cannot express it in numbers, your knowledge is of a meager and unsatisfactory kind: it may be the beginning of knowledge, but you have scarcely, in your thoughts, advanced to the stage of science.
—William Thompson Lord Kelvin, 1824–1907
I. Pain history
1. Pain assessment tools
2. Pain location
3. Pain etiology
II. Physical examination
1. General physical examination
2. Specific pain evaluation
3. Neurologic examination
4. Musculoskeletal system examination
5. Assessment of psychological factors
III. Diagnostic studies
Pain is a complex multidimensional symptom determined not only by tissue injury and nociception but also by previous pain experience, personal beliefs, effect, motivation, environment, and, at times, pending litigation. There is no objective measurement of pain. Self-report is the most valid measure of the individual experience of pain. The pain history is key to the assessment of pain and includes the patient’s description of pain intensity, quality, location, timing, and duration, as well as ameliorating and exacerbating conditions.
Frequently, pain cannot be seen, defined, or felt by the examiner, and the physician must assess the pain from a combination of factors. The most important of these is the patient’s report of pain, but other factors such as personality and culture, psychological status, the potential of secondary gain, and the possibility of drug-seeking behavior also deserve consideration. Reports of pain may not correlate with the degree of disability or findings on physical examination. It is important to remember, however, that to our patients and their families, distress, suffering, and pain behaviors are often not distinguished from the pain itself.
Acute pain diagnosis and measurement require frequent and consistent assessment as part of daily clinical care to ensure rapid titration of therapy and preemptive interventions. Chronic pain is often more diagnostically challenging than acute pain, but it is no less compelling. Application of a structured history and comprehensive physical examination will define treatable problems and identify complicating factors. Somatic, visceral, or neuropathic pain, or a combination of these problems, suggests specific diagnoses and interventions. An understanding of pain pathophysiology guides rational and appropriate treatment.
I. PAIN HISTORY
The general medical history may contribute significantly, and it is always included as part of the pain assessment (see Chapter 4). The specific pain history includes three main issues—intensity, location, and pathophysiology. The following questions help define them:
What is the time course of the pain?
Where is the pain?
What is the intensity of the pain?
What factors relieve or exacerbate the pain?
What are the possible generators of the pain?
1. Pain assessment tools
Pain cannot be objectively measured, and its intensity is very difficult and often frustrating to try to pinpoint. Several tests and scales are available. Some of the more commonly used are discussed here.
Unidimensional self-report scales
In practice, self-report scales serve as very simple, useful, and valid methods for assessing and monitoring patients’ pain.
VERBAL DESCRIPTOR SCALES. The patient is asked to describe his or her pain by choosing from a list of adjectives that reflect gradations of pain intensity. The five-word scale consists of mild, discomforting, distressing, horrible, and excruciating. Disadvantages of this scale include the limited selection of descriptors and the fact that patients tend to select moderate descriptors rather than the extremes.
VERBAL NUMERIC RATING SCALES. These are the simplest and most frequently used scales. On a numeric scale (most commonly 0 to 10, with 0 being “no pain” and 10 being “the worst pain imaginable”), the patient picks a number to describe the pain. Advantages of numeric scales are their simplicity, reproducibility, easy comprehensibility, and sensitivity to small changes in pain. Children as young as 5 years who are able to count and have some concept of numbers (e.g., “8 is larger than 4”) may use this scale.
VISUAL ANALOG SCALES. These are similar to the verbal numeric rating scales, except that the patient marks on a measured line, one end of which is labeled “no pain” and the other end, “worst pain imaginable,” where the pain falls. Visual scales are more valid for research purposes, but they are less used clinically because they are more time consuming to conduct than verbal scales.
“FACES” PAIN RATING SCALE. Evaluating pain in children can be very difficult because of the child’s inability to describe pain or understand pain assessment forms. This scale depicts six sketches of facial features, each with a numeric value, 0 to 5, ranging from a happy, smiling face to a sad, teary face (Fig. 1). To extrapolate this scale to the visual analog scale, multiply the chosen value by two. This scale may also be beneficial for mentally impaired patients. Children as young as 3 years may reliably use this scale.
Figure 1. Wong-Baker’s “faces” pain rating scale. Explain to the person that each face is for someone who feels happy because he has no pain (hurt) or sad because he has some or a lot of pain. Face 0 is very happy because he doesn’t hurt at all. Face 1 hurts just a little bit. Face 2 hurts a little more. Face 3 hurts even more. Face 4 hurts a whole lot. Face 5 hurts as much as you can imagine, although you don’t have to be crying to feel this bad.
Multidimensional instruments provide more complex information about the patient’s pain and are especially useful for assessment of chronic pain. As they are time consuming, they are most frequently used in outpatient and research settings.
McGill Pain Questionnaire (MPQ)
The MPQ is the most frequently used multidimensional test. Descriptive words from three major dimensions of pain (sensory, affective, and evaluative) are further subdivided into 20 subclasses, each containing words that represent varying degrees of pain. Three scores are obtained, one for each dimension, as well as a total score. Studies have shown the MPQ to be a reliable instrument in clinical research.
Brief Pain Inventory (BPI)
In the BPI, patients are asked to rate the severity of their pain at its “worst,” “least,” and “average” within the past 24 hours, as well as at the time the rating is made. It also asks patients to represent the location of their pain on a schematic diagram of the body. The BPI correlates with scores of activity, sleep, and social interactions. It is cross-cultural and a useful method for clinical studies (Fig. 2).
Figure 2. Brief pain inventory (see text). Reprinted with permission from the University of Wisconsin–Madison, Department of Neurology, Pain Research Group.
Massachusetts General Hospital (MGH)
Pain Center pain assessment form
The MGH form (Fig. 3) combines many of the preceding assessment instruments and is given to all patients on initial consultations at the MGH Pain Center. It elicits information about pain intensity, its location (via a body diagram), quality of pain, therapies tried, and past and present medications. It takes 10 to 15 minutes to complete and is an extremely valuable instrument. Its disadvantages are that it is time consuming to complete and it is not applicable if there are language constraints.
Figure 3. The Massachusetts General Hospital (MGH) Pain Center’s pain assessment form.
A diary of a patient’s pain is useful in evaluating the relationship between pain and daily activity. Pain can be described using the numeric rating scale, during activities such as walking, standing, sitting, and routine chores. Blocks of time are usually hourly. Medication use, alcohol use, emotional responses, and family responses may also be helpful information to record. Pain diaries may reflect a patient’s pain more accurately than a retrospective description that may significantly over- or underestimate pain.
2. Pain location
Knowing the location and distribution of pain is extremely important for understanding the pathophysiology of the pain complaint. Body diagrams, found in some of the assessment instruments, can prove very useful. Not only can the clinician view the patient’s perception of the topographic area of pain but the patient may demonstrate psychological distress by an inability to localize the pain or by magnifying it and projecting it to other areas of the body.
Is the pain localized or referred? Localized pain is pain that is confined to its site of origin without radiation or migration. Referred pain usually arises from visceral or deep structures and radiates to other areas of the body. A classic example of referred pain is shoulder pain from phrenic nerve irritation (causes include liver metastases from pancreatic cancer) (Table 1).
Table 1. Examples of referred pain
Is pain superficial/peripheral or visceral? Superficial pain, arising from tissues rich in nociceptors, such as skin, teeth, and mucous membranes, is easily localized and limited to the affected part of the body. Visceral pain arises from internal organs, which contain relatively few nociceptors. Visceral afferent information may converge with superficial afferent input at the spinal level, referring the perception of visceral pain to a distant dermatome. Visceral pain is diffuse and often poorly localized. In addition, it often has an associated autonomic component, such as diaphoresis, capillary vasodilation, hypertension, or tachycardia.
3. Pain etiology
By taking a complete history and answering the preceding two questions, the clinician can begin to formulate the causes of the pain. The rest of the history, as well as the physical examination, can be tailored to systematically explore aspects of pain, such as symptoms and physical signs, common to the particular type of pain in question.
It is possible to describe different types of pain, and they tend to present differently (e.g., nociceptive pain is associated with tissue injury caused by trauma, surgery, inflammation or tumor; neuropathic pain is invariably associated with sensory change; radicular pain is often associated with radiculopathy). The history and physical examination help to identify these differences. Because the different types of pain tend to respond to different treatments, the identification of pain type during pain assessment is important. The types can be categorized as follows:
Nociceptive pain arises from activation of nociceptors. Nociceptors are found in all tissues except the central nervous system (CNS); the pain is clinically proportional to the degree of activation of afferent pain fibers and can be acute or chronic (e.g., somatic pain, cancer pain, postoperative pain).
Neuropathic pain is caused by nerve injury or disease, or by involvement of nerves in other disease processes such as tumor or inflammation. Neuropathic pain may occur in the periphery or in the CNS.
Sympathetically mediated pain is accompanied (at some point) by evidence of edema, changes in skin blood flow, abnormal sudomotor activity in the regional of pain, allodynia, hyperalgesia, or hyperpathia.
Deafferentation pain is chronic and results from loss of afferent input to the CNS. The pain may arise in the periphery (e.g., peripheral nerve avulsion) or in the CNS (e.g., spinal cord lesions, multiple sclerosis).
Neuralgia pain is lancinating and associated with nerve damage or irritation along the distribution of a single nerve (e.g., trigeminal) or nerves.
Radicular pain is evoked by stimulation of nociceptive afferent fibers in spinal nerves, their roots, or ganglia, or by other neuropathic mechanisms. The symptom is caused by ectopic impulse generation. It is distinct from radiculopathy, but the two often arise together.
Central pain arises from a lesion in the CNS, usually involving the spinothalamic cortical pathways (i.e., thalamic infarct). The pain is usually constant, with a burning, electrical quality, and it is exacerbated by activity or changes in the weather. Hyperesthesia and hyperpathia and/or allodynia are invariably present, and the pain is highly resistant to treatment.
Psychogenic pain is inconsistent with the likely anatomic distribution of the presumed generator, or it exists with no apparent organic pathology despite extensive evaluation.
Referred pain often originates from a visceral organ (see Table 1). It may be felt in body regions remote from the site of pathology. The mechanism may be the spinal convergence of visceral and somatic afferent fibers on spinothalamic neurons. Common manifestations are cutaneous and deep hyperalgesia, autonomic hyperactivity, tenderness, and muscular contractions.
II. PHYSICAL EXAMINATION
A complete examination is required, including a general physical examination followed by a specific pain evaluation, and neurologic, musculoskeletal, and mental status assessments. It is important not to limit the examination to the painful location and surrounding tissues and structures.
1. General physical examination
This physical examination consists of the usual head-to-toe examination as described in Chapter 4. It is important to note the following points:
Appearance—obese, emaciated, histrionic, flat effect
Posture—splinting, scoliosis, kyphosis
Gait—antalgic, hemiparetic, using assistive devices
Expression—grimacing, tense, diaphoretic, anxious
Vital signs—sympathetic overactivity (tachycardia, hypertension), temperature asymmetries
It is also important to watch how a patient dresses and moves. Favoring an extremity or protecting a part of the body may not be appreciated unless the relevant movements are elicited. Some elements of the comprehensive examination may be missed if a clinician is fearful of invading the patient’s privacy.
2. Specific pain evaluation
After the general examination, the clinician evaluates the painful areas of the body. The history often directs the search for physical findings. Inspection of the skin may reveal changes in color, flushing, edema, hair loss, presence or absence of sweat, atrophy, or muscle spasm. Inspection of nails may show dystrophic changes. Nerve root injury may be manifest as goose flesh (cutis anserina) in the affected dermatome. Palpation allows mapping of the painful area and detection of any change in pain intensity within the area, as well as during the examination, and helps to define pain type and trigger points. Patient responses, both verbal and nonverbal, should be noted, as well as the appropriateness of the responses and their correlation with affect. Factors that reproduce, worsen, or decrease the pain are sought.
While conducting the physical examination, it is important to identify any changes in sensory and pain processing that may have occurred. These changes may be manifest as anesthesia, hypoesthesia, hyperesthesia, analgesia, hypoalgesia, allodynia, hyperalgesia, or hyperpathia.
3. Neurologic examination
Subtle physical findings are often found only during the neurologic examination. It is essential to conduct a comprehensive neurologic examination when first assessing a patient with pain, to identify associated, and possibly treatable, neurologic disease. The examination can be performed in 5 to 10 minutes. Later in the course of treatment, the neurologic examination can be more focused and briefer.
Mental function is assessed by evaluating the patient’s orientation to person, place, and time, short- and long-term memory, choice of words used to describe symptoms and answer questions, and educational background.
The cranial nerves should be examined, especially in patients complaining of head, neck, and shoulder pain symptoms. Table 2 lists the function of each cranial nerve.
Table 2. Neurologic examination of cranial nerves
A simple assessment of spinal nerve function should also be performed. Spinal nerve sensation is determined by the use of cotton or tissue paper for light touch, and pinprick for sharp pain and proprioception. Potentially painful peripheral neuropathies are listed in Table 3. Spinal nerve motor function is determined by deep tendon reflexes, the presence or absence of the Babinski reflex, and tests of muscle strength. Table 4 lists sensory and motor manifestations of common root syndromes.
Table 3. Painful sensory neuropathies
Table 4. Pain-induced disturbances of gait
Coordination is assessed by testing balance, rapid hand movement, finger-to-nose motion, toe-to-heel motion, gait, and Romberg’s test. Cerebellar dysfunction can often be detected during these maneuvers. Table 5 lists pain disturbances, caused by various disease processes, that can affect gait.
Table 5. Common painful root syndromes
Pain of psychogenic origin usually results in a neurologic examination whose findings are not typical of organic pathology. Abnormal pain distributions, such as glove or stocking patterns and exact hemianesthesia, are common in patients with psychogenic pain.
4. Musculoskeletal system examination
Abnormalities of the musculoskeletal system are often evident on inspection of the patient’s posture and muscular symmetry. Muscle atrophy usually indicates disuse. Flaccidity indicates extreme weakness, usually from paralysis, and abnormal movements indicate neurologic damage or impaired proprioception. Limited range of motion of a major joint can indicate pain, disc disease, or arthritis. Palpation of muscles helps in evaluating range of motion and in determining whether trigger points are present. Coordination and strength are also tested.
5. Assessment of psychological factors
Complete assessment of pain includes analysis of the psychological aspects of pain and the effects of pain on behavior and emotional stability. Such assessment is challenging, because many patients are unaware of or reluctant to present psychological issues. It is also more socially acceptable to seek medical than psychiatric care.
Initially, the use of a descriptive pain questionnaire, such as the MPQ, may provide some evidence of a patient’s affective responses to pain. For example, whereas words such as aching and tingling refer to sensory aspects of pain, words such as agonizing and dreadful suggest negative feelings and do not aid in characterizing the pain sensation. For a fuller description of psychological evaluation in pain management, see Chapter 15.
A patient’s personality greatly influences his or her response to pain and choice of coping strategies. Some patients may benefit from the use of strategies of control, such as distraction and relaxation. Patients who have an underlying anxiety disorder may be more likely to seek high doses of analgesics. Therefore, inquiry regarding a patient’s history of coping with stress is often useful.
As part of the pain history, the clinician should include questions about some of the common symptoms in patients with chronic pain: depressed mood, sleep disturbance, preoccupation with somatic symptoms, reduced activity, reduced libido, and fatigue. Standardized questionnaires, such as the Minnesota Multiphasic Personality Inventory (MMPI), may expand the assessment. On this inventory, patients with chronic pain characteristically score very high on the depression, hysteria, and hypochondriasis scales. However, the MMPI may reflect functional limitation secondary to pain as well as psychological abnormality associated with chronic pain, limiting its interpretation for some patients suspected of having psychogenic pain.
A number of psychological processes and syndromes predispose patients to chronic pain. Predisposing disorders include major depression, somatization disorder, conversion disorder, hypochondriasis, and psychogenic pain disorder. The diagnosis of somatization disorder is quite specific, although many patients with chronic pain may somatize (i.e., focus on somatic complaints). This diagnosis requires a history of physical symptoms of several years’ duration, beginning before the age of 30 years and including complaints of at least 14 specific symptoms for women and 12 for men. These symptoms are not adequately explained by physical disorder, injury, or toxic reaction.
Psychogenic pain may occur in susceptible individuals. In some patients, pain may ameliorate more unpleasant feelings, such as depression, guilt, or anxiety, and distract the patient from environmental stress factors. Features from the patient’s history that suggest a psychogenic component to chronic pain include the following:
Multiple locations of pain at different times
Pain problems dating since adolescence
Pain without obvious somatic cause (especially in the facial or perineal area)
Multiple, elective surgical procedures
Substance abuse (by patient and/or significant other)
Social or work failure
Psychogenic pain is clearly distinct from malingering. Malingerers have an obvious, identifiable environmental goal in producing symptoms, such as evading law enforcement, avoiding work, or obtaining financial compensation. Patients with psychogenic pain make illness and hospitalization their primary goals. Being a patient is their primary way of life. Such patients are unable to stop symptom production when it is no longer obviously beneficial.
The physical examination in patients with psychological factors exacerbating pain may be perplexing. Some findings may not correspond to known anatomic or physiologic information. Examples of such findings include the following:
Manual testing inconsistent with patient observation during sitting, turning, and dressing
Grasping with three fingers
Antagonist muscle contraction on attempted movement
Decreased tremor during mental arithmetic exercises
A positive Romberg’s sign with one eye closed
Vibration absent on one side of midline (skull, sternum)
Inconsistency of timed vibration when affected side is tested first
Patterned miscount of touches
Difficulty touching the good limb with the bad
A slight difference in sensation on one side of the body
Useful neurologic signs are deep tendon reflexes, motor tone and bulk, and the plantar response. Observation is critical. Pain drawings at multiple time intervals are also useful in evaluating a patient with chronic pain of unclear etiology.
III. DIAGNOSTIC STUDIES
The diagnosis and understanding of a patient’s pain complaint can usually be obtained after a thorough history and physical examination. Diagnostic and physiologic studies are used to support a clinician’s suspicion, as well as to assist in the diagnosis. Some of the more common studies used for pain assessment include the following.
Conventional radiography is used to diagnose bony abnormalities, such as pathologic fractures seen in bony metastases, spine pathology (including spondylolisthesis, stenosis, and osteophyte formation), and bone tumors. Some soft-tissue tumors and bowel abnormalities can also be seen. Radiographs of the painful area have usually been obtained by the referring physician.
A CT scan is most often used to define bony abnormalities, and MRI best shows soft-tissue pathology. Spinal stenosis, disc herniation or bulge, nerve root compression, and tumors in all tissues can be diagnosed, as well as some causes of central pain, such as CNS infarcts or plaques of demyelination.
Diagnostic blocks may differentiate somatic from visceral pain and confirm the anatomic location of peripheral nerve pain. They may help localize painful pathology or contribute to the diagnosis of complex regional pain syndrome (CRPS). They are also necessary precedents to neurolytic blocks for malignant pain or radiofrequency lesions. Diagnostic blocks are described in detail in Chapter 12.
Drug challenges are used to predict drug treatment utility and to help in the assessment of pain etiology. For example, brief intravenous infusions of opioids, lidocaine, and phentolamine are used to predict opioid sensitivity in nonmalignant chronic pain, to predict sensitivity to sodium channel blockade in neuropathic pain, and to assess the potential reversibility of the sympathetic component of pain in CRPS. The value of this type of testing in predicting treatment efficacy is debatable. In most reports, chronic treatment has been limited to responders, which precludes validation of the infusion as a predictive test.
Various neurophysiologic tests are used to help in the diagnosis of pain syndromes and related neurologic disease (see Chapter 7). The neurophysiologic tests most commonly used in pain clinics are categorized as quantitative sensory testing (QST), and these tests specifically evaluate patients’ responses to carefully quantified physical stimuli.
Thermography is a noninvasive way of displaying the body’s thermal patterns. A normal thermal pattern is relatively symmetric. Tissue pathology is associated with chemical and metabolic changes that may cause abnormal thermal patterns by altering vascularity, such as in CRPS. The differences in patterns of color are not specific for underlying central or peripheral pathology.
Myelography is the injection of radiopaque dye into the subarachnoid space to radiographically visualize spinal cord/column abnormalities, such as disc herniation, nerve root impingement, arachnoiditis, and spinal stenosis. Major disadvantages of this procedure are postdural-puncture headache and meningeal irritation.
Bone scanning is the use of a radioactive compound to detect bone lesions, including neoplastic, infectious, arthritic, and traumatic lesions; Paget’s disease; and the osteodystrophy of reflex sympathetic dystrophy. The radioactive compound accumulates in areas of increased bone growth or turnover. The test is very sensitive for subtle bone abnormalities that may not appear on conventional radiographs.
Small punch skin biopsy (immunolabeled to show the cutaneous sensory nerve endings) is a new tool with which to directly visualize the cutaneous endings of pain neurons. Although currently available at only a few centers, this technique is replacing sural nerve biopsy for the diagnosis of sensory neuropathies. The technique appears to be helpful for diagnosing focal painful nerve injuries. Research has shown that various painful neuropathic conditions are associated with loss of nociceptive innervation in painful skin. Skin biopsies are only minimally invasive, can be repeated, and can be performed in areas other than those innervated by the sural nerve.
Functional brain imaging , such as by positron emission tomography or functional MRI, is an investigative tool at present with provocative findings regarding the cortical and subcortical processing of pain information. Functional MRI shows pain to be a remarkably distributed system at the cortical level.
The assessment of pain can be challenging and intensive, but it is an essential component of pain management, and it allows the pain physician to devise optimal treatment for some of medicine’s most complex patients. The patient must be treated as a complete person and not just as a painful location. Believing the patient and establishing rapport are of the utmost importance. A systematic approach, grounded in a knowledge of anatomy and physiology, will assist the clinician in determining the pathophysiology of the patient’s pain complaint. Then, therapy can be formulated, promptly initiated, and easily reassessed.
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