Clinimetric evaluations of patients with chronic widespread pain

Assessing chronic widespread pain (CWP) and its impact on physical, emotional and social function requires multidimensional qualitative and health-related quality of life (HRQL) instruments. The recommendations of the Initiative on Methods, Measurement, and Pain Assessment in Clinical Trials (IMMPACT) concerning outcome measurements for pain trials are useful for making routine assessments, the most significant of which include pain, fatigue, disturbed sleep, physical functioning, emotional functioning, patient global ratings of satisfaction and HRQL. However, despite the growing spread of instruments and theoretical publications devoted to measuring the various aspects of chronic pain, there is little widespread agreement, and no unified approach has yet been devised. There is therefore still considerable scope for the development of consensus around a core set of measures and response criteria, as well as for the development and refinement of the related instruments, standardised assessor training, the cross-cultural adaptation of health status questionnaires, electronic data capture and the introduction of valid, reliable and responsive standardised quantitative measurements into routine clinical care. Clinicians need to be aware of the psychometric properties of the instruments used, including their levels of imprecision and minimum clinically important differences (those indicating a meaningful change in clinical status). This article reviews a selection of the instruments used to assess CWP patients, including validated newly developed and well-established screening instruments, and discusses their advantages and limitations.

Chronic widespread pain (CWP) is prevalent and co-occurs with numerous symptom-based conditions, including chronic fatigue syndrome, musculoskeletal disorders, headache, irritable bowel syndrome and psychiatric disorders . The symptoms are persistent and the people suffering from them are long-term, frequent seekers of medical advice, thus leading to high direct and indirect health-care costs . The American College of Rheumatology (ACR) criteria for CWP are met if all of the following symptoms persist for at least 3 months: pain in the left side of the body, pain in the right side of the body, pain above the waist and pain below the waist; in addition, the presence of axial skeletal pain affecting the cervical spine, anterior chest, thoracic spine or lower back is also required .

Patients with CWP are frequently encountered in clinical practice, but their assessment can be a formidable challenge because of the wide range of possible rheumatological, endocrine/metabolic, neurological, infectious, malignant or psychiatric diagnoses . CWP has always been an important factor for rheumatologists, as it occurs in a significant percentage of their patients. The findings of population-based studies in the USA and UK suggest that approximately 10–11% of the population experiences CWP at any given time .

An extreme form of CWP is fibromyalgia (FM) , a complex multifactorial disorder characterised by persistent widespread pain with mechanical hyperalgesia at >11 tender points, often accompanied by associated symptoms such as fatigue, sleep disturbances, psychological and cognitive alterations, headache, migraine, variable bowel habits, diffuse abdominal pain and urinary frequency . It affects at least 2% of the general population in Italy, and more than 90% of the patients are female .

There is a consensus that CWP clinical trials should assess outcomes representing four core chronic pain outcome domains: (1) pain intensity; (2) physical functioning; (3) emotional functioning; and (4) trial participant ratings of overall improvement . These core outcome domains specified in the Initiative on Methods, Measurement, and Pain Assessment in Clinical Trials (IMMPACT) consensus recommendations are generally consistent with the recommendations of the Consolidated Standards of Reporting Trials (CONSORT) guidelines , the Outcome Measurement in Rheumatoid Arthritis Clinical Trials (OMERACT) and the World Health Organization/International League of Associations for Rheumatology (WHO/ILAR) .

Given the multifaceted nature of CWP and the new therapies currently being tested , there is a need to refine these domains further to develop a reliable and valid composite patient-reported outcome (PRO) response measure that more accurately assesses treatment effects. The validity, reliability and responsiveness of PRO data in evaluating and monitoring patients with rheumatic conditions have been clearly documented .

This review considers the methodological issues concerning the clinimetric properties of a number of instruments currently used to assess patients with CWP that are dimension specific and symptom specific, and include measurements of widespread pain, fatigue, sleep disturbance, mood and overall well-being. It is not exhaustive, but is based on an extensive search of the literature and the knowledge and experience of a multidisciplinary group of authors, and is intended to provide recommendations for daily clinical practice.

Pain assessment

Assessing chronic pain is important in both clinical research and practice , and involves determining the mechanisms of pain by documenting pain intensity, location, quality and onset/duration, functional ability and psychological/social factors such as depression or anxiety by means of individually appropriate pain assessment instruments. Self-reporting is the primary source, and facilitates regular reassessment and follow-up .

Single-dimension assessment pain scales

In busy clinical settings, the instruments for measuring pain must be simple, quick to administer and easily understood by patients. Unidimensional scales provide rapid measures and can be administered multiple times with minimal administrative effort ( Table 1 ).

Table 1

Single-dimension assessment instruments.

Scale	Administration	Indications	Characteristics
Visual analogue scales (VAS)	Visual	Chronic pain, rheumatic disease in children aged >7 yrs	Poor reproducibility postoperatively or in patients with cognitive dysfunction or dementia
Numeric rating scales (NRS)	Verbal or visual	Chronic pain, rheumatic disease, trauma, cancer, illiteracy	Detect treatment effects. Less reliable at extremes of age, in pre-verbal patients or those with visual, auditory or cognitive dysfunction
Visual numeric scales (VNS)	Visual	Chronic pain, rheumatic disease, trauma, cancer, illiteracy	Easier for older adults
Graphic rating scales (GRS)	Visual	Chronic pain, rheumatic disease in children aged >7 yrs	Less reliable in illiterate patients
Descriptive verbal scales (DVS)	Verbal or visual	Adults	Easier for older adults
Faces pain scale (FPS)	Visual	Adults, children	Easier than NRS or VAS, not affected by culture, gender or ethnicity

One commonly used unidimensional instrument is the visual analogue scale (VAS) . Although variations exist, this typically consists of scores from 0 to 10 (or from 0 to 100), with the far left being described as “no pain” and the far right as “worst pain imaginable” ( Fig. 1 ). VASs provide a high degree of resolution and are probably the most widely used single-item measure in clinical pain research . However, they are sometimes criticised as being difficult to understand, leading to 7–16% higher failure rates than those reported for verbal rating scales (VRS) or numerical rating scales (NRS) , a problem that is exacerbated in subjects with physical or cognitive impairment and in the elderly . Evidence shows that the visuospatial abilities required for the use of VAS are more affected by age than the lexical abilities required for use of a VRS or NRS . VASs are also less reliable in illiterate patients.

Understanding may be improved by the addition of markers to form a graphic rating scale (GRS; Fig. 1 ). These scales include a horizontal line that is anchored at both ends (“no pain” and “worst pain imaginable”) and graded 0–10 (or 0–100), and has vertical bars of increasing height. Studies in other fields of medicine indicate that the anchors improve reliability and sensitivity, and do not necessarily lead to excessive marker bias (i.e., the tendency to be “drawn” towards the markers when completing the scale).

Another alternative is an NRS ( Fig. 1 ) numbered 0–10, which may be more practical, easier to understand for most people and does not need clear vision, dexterity or paper and pen . It is also possible to determine the intensity of pain accurately using a normal or computerised telephone interview (in the latter case, patients record the data directly into a database via their telephone keyboard). Pincus et al. found that a circle with 21 numbers and an arithmetic scale offers an optimal alternative to a 10-cm horizontal line, over which it has at least three advantages: (1) it can be scored without a ruler, thus saving about half the time; (2) it eliminates the need to reproduce an exact 10-cm line when printing or photocopying questionnaires, thus averting the problem of the minor distortions; and (3) patients seem to understand how to respond better (some patients write words or even sentences on a line). The measurement properties of a 21-number circle have also been evaluated in terms of physician and parent subjective ratings in children with juvenile idiopathic arthritis .

A further alternative is a descriptive verbal scale (DVS), which consists of a list of adjectives describing different levels of pain intensity, and is sometimes used for subjects, who have difficulty in translating their pain experience into a number ( Fig. 1 ). It includes adjectives that reflect the extremes (e.g., “no pain” to “severe pain”) and sufficient adjectives to capture gradations in between. A DVS is usually a 4- or 5-point scale, and patients are asked to select (in a questionnaire or verbally) the adjective that best describes the intensity of their pain. However, this type of measure has a number of statistical drawbacks and is usually used only as a coarse screening instrument .

The VAS and NRS agree well and are equally sensitive in assessing pain, and they are both superior to a 4-point DVS, but clinical trials have shown that NRSs are more reliable, especially with less educated patients . The simplicity and ease of obtaining pain ratings is an overriding criterion for pain assessment in clinical settings, as shown by the prevalence of the use of a simple 0–10-cm NRS .

A number of other single-item scales have been developed and tested. The Faces Pain Scale (FPS), which was originally developed for use in children, incorporates schematic faces depicting increasing pain severity, each of which is associated with a number between 0 and 5 or 6 . This scale also seems to be a valid and reliable instrument for use in the elderly, although it is not necessarily preferable to a VRS or NRS .

Other scales put numbers, descriptive words and colours along a VAS, and include the Visual Numeric Scale (VNS), the Anchored Logarithmic Scale, the Analogue Chromatic Continuous Scale (ACCS) and ‘pain thermometers’ or ‘pain rulers’ ( Figs. 2 and 3 ) . The VNS was developed to take advantage of the features of numeric scales, while providing multiple visual cues, including the height and shading of the bars associated with each number ( Fig. 2 ), and can thus be considered a combined visual and numeric scale .