Pain assessment in clinical trials: a narrative review

Pain is a symptom measured in many clinical trials. For pain as an outcome domain, trialists need to choose adequate outcome measure(s), as there are myriad outcome measures for pain to choose from. To ensure consistency and uniformity in clinical trials and systematic reviews, core outcome sets (COS) have been defined; COS includes a predefined minimal list of core outcomes that should be measured within a trial, to ensure their consistency and comparability. COS is defined via consensus procedure, which includes relevant stakeholders such as experts from a specific field and patients. Along with outcomes, outcome measures for each outcome need to be defined to make sure that the outcomes will be measured consistently and uniformly. Hereby we reviewed studies that have examined use of recommended core outcome domains and outcome measures in clinical trials that would be expected to measure pain. Despite the existence of COS and defined core outcome measures (COMs), multiple studies have shown that these are not necessarily used in clinical trials, or in the relevant systematic reviews, which further increases heterogeneity of existing evidence, hinders evidence synthesis and trial comparability, and assessment of comparative effectiveness of interventions. Trialists are encouraged to use COS and COMs when designing clinical trials. Research community is encouraged to design interventions that will help with identifying barriers for using COS and COMs and interventions to foster their uptake. Use of consistent pain outcomes and pain outcome measures is in the interest of patients, research community, healthcare workers and decision-makers. For clinical conditions for which there are no COS and COMs, efforts to design them would be beneficial.