Assessment of Pain 1

By Prof. Tissa Wijeratne, Dr. Ranjith Pallegama

and Dr. Dilani Wijeratne

 

Introduction

     Pain is the most common symptom observed in a regular medical practice. According to epidemiological studies in the west, it is estimated that 20% of the adult population suffers from pain.

     Pain can be clinically classified as either nociceptive or neuropathic, although sometimes these may coexist. Nociceptive pain arises from mechanical, chemical or thermal irritation of peripheral sensory nerves (e.g. after surgery or trauma, or associated with degenerative processes such as osteoarthritis or inflammatory processes such as acute exacerbation of gout). Typically, the nociceptive pain is described as sharp and well localized.

     Nociceptive pain, especially when acute, serves an essential bio-protective function. It helps to localize and identify the nature of a painful stimulus which helps in avoidance of potentially tissue damaging events. Neurological disorders with severe reduction or absence of pain demonstrates the importance of this function. Significant tissue damage that may occur in peripheral disorders like diabetic neuropathy and leprosy may give rise to such perilous situations.

     Neuropathic pain has quite different clinical features with poor localization. Neuropathic pain is defined as pain initiated or caused by a primary lesion or a dysfunction in the nervous system. This is often associated with the appearance of abnormal sensory signs with clinical characteristics of allodynia (pain as a result of a stimulus which does not normally provoke pain) and/or hyperalgesia (an increased response to a stimulus which is normally painful).

     Pain is a subjective experience which is determined by tissue injury and nociception, previous pain experience, personal beliefs, affect, motivation, environment and other social factors such as work related /litigation related issues. There is no objective measurement of pain.

     There are several approaches to the measurement and assessment of pain. These include, self-rating scales such as verbal, numerical and visual analogue scales, physiological responses, and behavioral observation scales. Measurement of pain is important to determine the severity, duration and the quality of pain. Measurement of pain   is also important to uncover the underlying etiology of pain, and to determine the best available treatment and effectiveness of these available treatments.

     Pain is understood to be a multidimensional experience. Melzack and Casey (1968) described three major psychological dimensions of pain: sensory-discriminative, motivational-affective and cognitively-evaluative.

     The sensory discriminative dimension of pain was thought to be primarily influenced by rapidly conducting spinal systems. The motivational drive and unpleasant affect characteristics of pain are thought to be primarily influenced by reticular and limbic structures which are neocortical or higher central nervous system processes.  Evaluation of the input in terms of past experiences exerts control over activity   in both the discriminative and motivational system. Sensory-discriminative, motivational affective and cognitively-evaluative categories could influence motor mechanisms responsible for the complex pattern of overt responses that characterizes pain.

 

Pain History

     Taking a good, detailed, clinically relevant medical history is a fundamental and an important part of the pain assessment. Specific pain history addresses following seven key issues.

Where is the pain?

What is the temporal profile of pain (acute/ sub acute/ chronic)?

What is the severity of pain?

What factors exacerbate pain?

What factors relieve pain?

What are the other associated symptoms with the current pain?

What is the possible origin of pain?

 

Pain Rating Scales

     Verbal rating scales, numerical rating scales and visual analogue scales provide a simple and efficient measure of pain intensity (a unidimensional assessment of pain).

 

Verbal rating scales

     The patient is asked to describe his/her pain by choosing a verbal descriptor from the least to most intense on a Likert scale (e.g. no pain, mild pain, moderate pain and severe pain). Patient can choose the word that best describes his/her pain (Figure 1).

 

Numeric rating scales

     These are the most simple and frequently used scales. These scales consists of a series of numbers ranging typically from 0 to10 or 0 to 100, with 0 being no pain and 10 or 100 being “ the worst pain imaginable” respectively. Patients choose the number that best corresponds to the intensity of their pain at the time. Children as young as five years (provided the children have some sense and concept of numbers and able to count) can use this scale.   Numerical rating scales provide the advantage of simplicity, easy comprehensibility and sensitivity to pick up even small intensity changes in pain (Figure 2).

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Visual analogue scales

     The advantages associated with the visual analogue scales (VAS) make them the measurement of choice when a unidimensional measure of pain is needed in clinical practice or research. VAS are similar to numeric rating scales with the exception that the patient marks on a measured line (usually of 100 mm in length), of which, one end is labeled “no pain at all” and the other end as “worst pain imaginable”—these are called anchor words—to describe his/her pain.

     A major advantage of VAS as a measure of sensory pain intensity is its ratio scale properties. Ease, simplicity and brevity of administration and scoring, greater sensitivity to detect effects of treatment include other advantages. Gagliese and Melzack (1997) reported that elderly patients with chronic pain make fewer errors on a verbal rating scale in comparison to a VAS. Gagliese and Katz (2003) reported that the VAS may not be as sensitive in detecting age differences in post-operative pain as are other measures.

    Unfortunately the assumption that pain is unidimensional experience and that pain can be measured with a single item is the main disadvantage of all the scales described above. As previously described, the word “pain” refers to an endless variety of qualities and types in experience. Pain does not mean a specific, single sensation that change only in intensity. For example, pain of a myocardial infarction is uniquely different from that of an acute attack of migraine.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

     Further, in measuring pain in children, pictorial scales are commonly used (figure 4). The Faces Pain Scale - Revised developed by IASP has been a valid and reliable tool for assessing pain in child patients. It has shown close linear relationship with visual analog pain scales across the age range 4 through 16 years. This tool is freely available for use and downloadable from developer’s website. But assessing pain in  toddlers is a  daunting task. It   expected   that    their behavior can express their emotions although they are unable to communicate their feelings. They become verbally aggressive, cry and withdraw from activity and physically resist and perhaps guard the painful area of the body. Lack of sleep can also be indicative of presence of pain (Figure 4).

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Multidimensional Assessment of Pain

 

 

 

     A detailed assessment of psychological status will provide a rational basis for more appropriate multidisciplinary approach to the management of patients. A complete assessment, especially in patients with chronic pain, will include aspects such as cognitive functions, mood (depression and anxiety), affect, thought process and content judgment, cognitions and beliefs (e.g. self-efficacy, locus of control, acceptance of pain, catastrophizing, belief about the link between pain and injury), disability (interference in daily activities), pain behaviors (e.g. limping, and use of canes or crutches), and use of pain coping strategies (avoidance, taking drugs, resting and overexertion). There are specific tools available for assessment of many of these aspects. Given below are a few tools that are commonly used for a general multidimensional assessment of pain patients.

 

McGill pain questionnaire (MPQ)

     Melzack and Torgerson (1971) pioneered the procedures to address the qualities of pain in detail. They obtained 102 words from the clinical literature. Physicians and other university graduates were then asked to classify these 102 words in to smaller groups that describe different aspects of pain. Subsequently the words were categorized in to three major classes and 16 subclasses.

     These classes included words that describe the sensory qualities (in terms of temporal, spatial, punctuate pressure, incisive pressure, constrictive pressure, traction pressure, thermal, brightness), words that describe affective qualities (in terms of tension, fear etc.) and evaluative words (mild, annoying, discomforting, distressing, horrible, unbearable and excruciating etc.).

     Melzack and Torgerson then conducted further studies to determine the pain intensities implied by the words within each subclass. McGill pain questionnaire (MPQ) was developed as a result of these studies. MPQ is the most frequently used multidimensional tool in pain assessment. Descriptive words from  sensory, affective and evaluative  dimensions of pain are further subdivided in to 20 subclasses , each containing varying degrees from 0-5 ( 0= no pain, 1= mild , 2= discomforting, 3= distressing, 4= horrible, 5= excruciating). Scores are obtained for each of the subclasses and a total score is calculated.

     MPQ is a simple tool that can also be filled out by the patients. It has been translated into several other languages such as Arabic, Chinese, Danish, Finnish, Spanish, Slovak, Portuguese, Polish, Japanese, Italian, and French, to name a few.

 

Short- Form McGill pain questionnaire (SF-MPQ)

     Melzack (1987) came up with the SF-MPQ as a tool for use in specific research settings when the time to obtain information from the patients is short. SF-MPQ has 15 subclasses from sensory (11) and affective (4) categories of the standard MPQ.

 

Brief pain inventory

     Brief pain inventory (BPI) was originally developed by the pain research group of the World Health Organization Collaborating Centre for Symptom Evaluation in Cancer Care to measure pain severity and pain related interference in patients with cancer. In BPI, patients are asked to rate their pain from “least”, “average”, to “worst” within the past 24 hours. Patients will represent the location of their pain on a schematic diagram of their body. BPI is widely used in measurement of cancer pain.