Since 2002, a multidisciplinary group of international experts — called the Initiative on Methods, Measurement, and Pain Assessment in Clinical Trials (IMMPACT) — has been meeting and developing consensus reviews and recommendations for improving the design, execution, and interpretation of clinical trials of treatments for pain. An important focus has been on chronic pain and how effective treatment outcomes can be defined and measured in clinical trials, as well as how research results translate to clinically meaningful outcomes.
The latest publication from the IMMPACT group [Dworkin et al. in press] notes that change in pain intensity typically serves as a primary efficacy endpoint in clinical trials and is an important measure of treatment effectiveness in everyday clinical practice. Various approaches to quantifying changes in pain intensity have been developed, with measures of patient-reported differences from baseline on either a numerical rating scale (NRS) or visual analog scale (VAS) being widely accepted assessment tools. The NRS has patients rank their pain by number, from 0 (none) to 10 (worst pain imaginable); the VAS has patients mark their pain intensity along a line (usually 100 mm long, from 0 [no pain] to 100 [worst imaginable]). Multiple analyses have confirmed that patients view clinically relevant reductions in pain intensity as follows: [Dworkin et al. 2008]
- substantial improvement = 4 or more points reduction on NRS, or 50% or more reduction on VAS;
- moderately meaningful = 2 points reduction (NRS), or 30-36% reduction (VAS);
- minimally important = 1 point reduction (NRS), or 10-20% reduction (VAS).
Further research has demonstrated that there are additional dimensions of chronic pain and its treatment beyond pain relief that are of clinical importance to patients and worthy of consideration. In cooperation with the American Chronic Pain Association, the IMMPACT group conducted a survey to identify important outcome domains [Turk et al. 2008]. The first part of this investigation identified 19 aspects of life that patients believe are significantly and negatively impacted by chronic pain syndromes. In the second part, 959 respondents with chronic pain selected the following out of the 19 as being most problematic and, therefore, essential targets for improvement: (1) common physical activities (eg, walking, climbing stairs), (2) weakness, (3) fatigue (feeling tired), (4) difficulty concentrating, (5) staying asleep at night, (6) emotional well-being (eg, feeling sad, depressed, unmotivated), and (7) overall enjoyment of life. The high rankings of these areas in importance were remarkably consistent across all chronic pain conditions represented, including arthritis (OA and RA), migraine, low back pain, neck or shoulder pain, neuropathy, and fibromyalgia.
Turk and colleagues  note that it may be unrealistic to expect that a treatment targeting reductions in pain intensity (analgesic effects) should also have beneficial effects on other dimensions, such as fatigue, weakness, depression, etc. “Just because patients desire change in various pain-related aspects of their functioning does not mean that the efficacy or effectiveness of a pain treatment should be measured by its effects on these other outcomes,” they write. However, it seems reasonable that knowledge of the pain-related domains that patients themselves regard as important, and the degree of change considered as clinically meaningful to them, can help in developing treatment plans and assessing therapeutic success. In the final analysis, armed with an appreciation of what is most important to individual patients, healthcare providers are better able to tailor therapies that best meet patient expectations — with the understanding that, as statistician Darrell Huff suggested in 1954, “…a difference is a difference only if it makes a difference.” We would welcome comments from practitioners sharing their opinions or perspectives.
References: documents are available for free access at http://immpact.org/publications.html.
> Dworkin RH, Turk DC, McDermott MP, et al. Interpreting the clinical importance of group differences in chronic pain clinical trials: IMMPACT recommendations. Pain. 2009 (in press).
> Dworkin RH, Turk DC, Wyrwich KW, et al. Interpreting the clinical importance of treatment outcomes in chronic pain clinical trials: IMMPACT recommendations. J Pain. 2008;9:105-121.
> Turk DC, Dworkin RH, Revicki D, et al. Identifying important outcome domains for chronic pain clinical trials: an IMMPACT survey of people with pain. Pain. 2008;137:276-285.
For Additional Information See...
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