Pain assessment measures

The third important aspect of all pain evaluation proto cols is the assessment of the intensity and quality of pain. Verbal, numerical, and visual analog scales are commonly used to assess the intensity of pain. Verbal rating scales consist of a list of adjectives that describe different levels of pain intensity. The patient is asked to choose the adjective, from as few as four to over ten depending on the scale used, that best describes his or her pain. Verbal rating scales are easy to administer, score, and understand, but are less sensitive than visual analog scales because of fewer response categories which may miss small changes in pain intensity.14 They assume fluency in communicating in a particular language and are not appropriate for preverbal patients or patients with cognitive impairments.

Numerical rating scales are based on asking pain patients to rate their pain from 0 to 10 or 0 to 100, with the anchor descriptors of "no pain'' and "worst imaginable pain.'' Numerical rating scales are easy to administer, score, and understand, and have demonstrated their validity as pain intensity measures.15

Visual analog scales usually are 10-cm lines, with defined anchors at the ends of the line ranging from "no pain'' to "worst pain imaginable.'' The patient is required to make a mark along the line that best reflects their pain intensity. Scoring is accomplished by measuring the distance from the left end of the scale to the mark. Although there is demonstrated validity with this technique, both very young and older patients have difficulty with this method,15 and photocopied versions change the length of the line.14 Visual analog scales are effective, however, with an older pediatric population.16[III]

In the pediatric setting, age-appropriate pain intensity measures have been devised for the different developmental stages of the child. The Poker Chip Tool17 requires that the four- to eight-year-old chooses one to four poker chips, representing the "pieces of hurt'' experienced. Various faces scales have also been devised for young children, with each face being assigned a numerical value reflecting its order within a series of facial expressions. Excellent psychometric properties have been demonstrated.18

One of the most commonly used pain assessment measures is the McGill Pain Questionnaire (MPQ).19 When it first appeared, it differed significantly from standard pain intensity measures, in that it offered, for the first time, a multidimensional assessment of pain -evaluating the sensory, affective, and evaluative dimensions of pain. Patients are asked to choose an adjective from each of 20 subclasses of adjective groupings. Each word is associated with a specific score. Pain-rating indices are calculated for the total score, as well as for each dimension. The MPQ is useful in differentiating psychiatric patients from those who do not have a psychiatric disturbance, and particularly in its ability to discriminate between patients who have different kinds of pain. For example, postherpetic neuralgia (PHN) is often described using the adjectives "tender, burning, throbbing, stabbing, shooting, sharp,'' which correlate with the three different types of pain experienced with PHN:

1. steady throbbing or burning pain;

2. an intermittent sharp or shooting pain;

3. allodynia (tender), (pain in response to a stimulus that does not normally provoke pain).

Confirmatory factor analyses of the MPQ have shed some doubt on the original three subscales of the test.20 Holroyd et al.,21 conducting a multicenter evaluation of the MPQ with 1700 chronic pain patients, showed that a factor analysis revealed a four-factor model instead of three factors: one affective, one evaluative, and two sensory factors. Furthermore, examination of the relationships between the MPQ and the Minnesota Multi-phasic Personality Inventory (MMPI) failed to provide evidence of the discriminant validity of the MPQ subscales. They concluded that the utility of the three scale scores in clinical decision-making remains unstan-dardized and the value in diagnosis or in forming useful subgroups of patients remains unclear.

Administration of the test needs to be carefully monitored, to make sure that no more than one word is selected from each subclass and to ensure that the patient understands each word. Patients for whom English is not their first language have particular difficulty with this test, although foreign language versions are available. The short form (SF-MPQ) has gained in popularity due to its brevity and good reliability.22 The SF-MPQ consists of 15 representative words from the sensory and affective categories of the original MPQ as well as an additional word "splitting'' because it is a discriminant word for dental pain. The SF-MPQ is sensitive to clinical changes from therapeutic interventions.23[II]

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