As technological advances in medicine have progressed from the measurement of temperature to the ability to test for genetic factors that can predispose to disease, physicians have sought objective measures for their patient’s problems. When it comes to pain, however— the most common complaint that drives patients to see doctors—we still rely on the subjective report of the individual patient as the primary measure.
We do have many instruments that help the patient quantify the sensation. They range from relatively simple measures of pain severity that can be administered in 1 or 2 minutes to the more complex, multidimensional scales that can take up to 20 minutes or longer to complete.
The Simplest Instruments
The most commonly used pain measurement scales of this type— which can be used to assess acute or chronic pain— are:
* The Numeric Pain Intensity (NPI) Scale: patients rate their pain from 0 (no pain) to 10 (worst possible pain)
* The Verbal Pain Intensity (VPI) Scale: patients are asked whether their pain is mild, moderate, or severe
* The Visual Analog Scale (VAS): patients make a mark on a 10-cm line to indicate pain intensity
* The Faces Pain Scale: patients are shown a continuum of cartoon faces with expressions that range from smiling to frowning and are asked choose the expression that best matches their pain. This scale was developed to measure pain in young children but has been found useful also to help assess pain in cognitively impaired geriatric patients.
The choice among the NPI, VPI, and the VAS is up to the individual practitioner. I recommend choosing the one that is easiest for you to administer and that you will use most often. I personally prefer the NPI; the 0-to-10 scale provides a little more detail than the 3-point VPI measure and doesn’t require me to carrry additional paper printed with the 10-cm VAS scale. Also, responses to the NPI can be easily charted, unlike the VAS.
More Complex Instruments
There are many complex instruments for measuring pain and virtually all are used to assess patients with chronic pain.
The most commonly employed are:
* McGill Pain Questionnaire (MPQ). A multifactorial instrument that assesses pain and its impact on patients’ lives in a variety of ways:
o Pain location – the patient marks the location of the pain on a figure drawing
o Pain quality – the patient selects words from 20 lists of words that are grouped to describe sensory, affective, evaluative, and miscellaneous qualities. There are 78 words to choose from.
o Temporal properties of pain – the patient selects words such as “continuous” or “transient”
o Pain intensity – the patient responds to both a 5-word descriptive scale and the NPI
An abbreviated form of the MPQ is available that includes a shorter word list and the pain intensity scales.
* Brief Pain Inventory (BPI). A 32-question instrument originally developed to assess pain in patients with cancer that has also been widely used for patients with chronic pain from other sources. It includes:
A section that inquires about demographics and medical history
o A figure drawing to note location of pain
o Numeric scales to assess pain at its best and worst during the past week and at the present time.
A section that asks about:
o What improves or exacerbates the pain
o Current treatments and their benefits
o Nature of the pain (a 15-word list of possible descriptors)
o Impact of pain on 7 areas of the patient’s life, such as general activity, mood, work, and enjoyment of life
A shorter form of the BPI is available that excludes the descriptive word sets and
most of the questions on response to treatment.
There are also instruments designed to assess specific forms of pain. Some examples are:
* Oswestry Low Back Pain Disability Questionnaire. This assesses the degree of impact this form of pain has on various aspects of patients’ lives, including walking, sitting, standing, sleeping, sex life, social life, travelling, personal care, and lifting; it also asks whether and to what extent “pain killers’ have an impact on the pain.
* Neuropathic Pain Questionnaire (NPQ). Multiple questions about various sensations believed to indicate this form of pain, such as “burning,” “electric shocks,” or “shooting pain.”
Do Complex Instruments Measure Pain More Accurately?
This is an unanswered question. More detailed instruments ask more questions, and they also provide more options for answering them. In many cases this includes more words to choose from to describe the pain. People with higher levels of education and broader vocabularies are likely to choose more words. This doesn’t imply, however, that their pain is greater or that they are suffering more than those whose vocabularies are more limited.
Use of the more complex instruments generally is limited to pain management programs and research. In other clinical settings the additional time required to administer and score them makes their use impractical. This is especially important since many of the questions they include—particularly those about the impact of pain on patients’ lives and on response to treatment—should already be a part of the initial clinical interview.
I believe it is far better to use the 0-to-10 NPI scale consistently than to use a more complex instrument intermittently.
An Important Final Issue
All of the instruments described and others that are available are useful for assessing individual patients and following them over time. However, it is important that they not be used to compare patients with each other in clinical practice. If one patient scores his or her pain as a “5” on the NPI and the next patient a “10,” it cannot be inferred that the former patient has half as much pain as the latter, or that the latter is exaggerating his pain. Unfortunately, I have often seen patients receive reduced amounts of pain medication because other patients with similar problems are reporting less pain.