Measuring Clinically Meaningful Outcomes in Chronic Pain Clinical Trials

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Standardized and clinically meaningful outcome measures in clinical trials in chronic pain may enhance efforts to develop effective treatments for chronic pain patients.

ORLANDO — Standardized and clinically meaningful outcome measures in clinical trials in chronic pain may enhance efforts to develop effective treatments for chronic pain patients. Diane Flynn, MD, MPH, from Madigan Army Medical Center, outlined the current recommendations for outcome measures in clinical trials for chronic pain at the American Academy of Pain Medicine (AAPM) 33rd Annual Meeting in Orlando, Florida.1

Clinical trials for chronic pain often use different outcome measures, making it difficult to compare the efficacy of different interventions. The method of determining treatment benefit must also be considered, since a statistically significant benefit may be clinically meaningless. In area of chronic pain, whether a treatment response is clinically meaningful is best determined by the patient.2

To address the variability in chronic pain research, the Initiative on Methods, Measurement, and Pain Assessment in Clinical Trials (IMMPACT) proposed the following core chronic pain outcome domains to serve as standard outcome measures: pain intensity, health-related quality of life as defined by physical functioning and emotional functioning, and ratings of overall improvement.2 These domains also capture whether a treatment provides a clinically important benefit as experienced by the patient.2

Likewise, the National Institutes of Health (NIH) Task Force recommends evaluating the impact of interventions for low back pain using the following domains: pain intensity, pain interference, and physical function.3 These domains may be measured with the Patient Reported Outcomes Measurement Information System (PROMIS) methodology known as the Pain Impact Score.3 The Pain Impact Score is also useful for trials evaluating patients with chronic musculoskeletal pain.4

Whether an outcome measure is clinically meaningful may also be determined by establishing the minimal important difference (MID), which is defined as “the smallest difference in score in the domain of interest that patients perceive as important, either beneficial or harmful, and which would lead the clinician to consider a change in the patient’s management.”5

Clinical trial outcomes must also be relevant for the population studied for results to be clinically meaningful. Relevant outcomes may include return to play for athletes or return to work for the Workers’ Compensation population.

The way in which outcomes are measured also affects the applicability of clinical trial results.2 According to Dr Flynn, IMMPACT recommends determining the effectiveness of pain interventions by evaluating treatment differences before and after treatment in the same individual rather than between treatment groups. The impact of the intervention on a population level may then be quantified by calculating the number needed to treat.

“This approach is more easily interpreted by providers and patients,” Dr Flynn said.

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  1. Flynn D. FRP: Is the juice worth the squeeze? Selecting outcomes relevant to your population. Presented at: the American Academy of Pain Medicine 33rd Annual Meeting; March 16-19, 2017; Orlando, Florida.
  2. 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(2):105-121. doi: 10.1016/j.jpain.2007.09.005
  3. Deyo RA, Dworkin SF, Amtmann D, et al. Report of the NIH Task Force on research standards for chronic low back pain. J Pain. 2014;15(6):569-585. doi: 10.1016/j.jpain.2014.03.005
  4. Deyo RA, Katrina Ramsey, Buckley DI, et al. Performance of a Patient Reported Outcomes Measurement Information System (PROMIS) short form in older adults with chronic musculoskeletal pain. Pain Med. 2016;17(2):314-324. doi: 10.1093/pm/pnv046
  5. Guyatt GH, Osoba D, Wu AW, Wyrwich KW, Norman GR; Clinical Significance Consensus Meeting Group. Methods to explain the clinical significance of health status measures. Mayo Clin Proc. 2002;77(4):371-383. doi: 10.4065/77.4.371