TEC Assessment Index

Special Report: Measuring and Reporting Pain Outcomes in Randomized Controlled Trials

Assessment Program
Volume 21, No. 11
October 2006

Executive Summary

Background
The burden of chronic pain for individuals and the population is substantial. Defining the effectiveness of interventions designed to ameliorate pain and its functional consequences poses challenges in the design, conduct, analysis, and reporting of randomized controlled trials (RCTs). Appraising results from these RCTs presents important issues not encountered in other settings.

Objectives
The first objective of this report is to examine key methodological elements related to measuring and reporting chronic pain outcomes in RCTs. The second is to systematically review studies that attempt to estimate the minimal clinically important difference (MCID) in change in pain intensity among patients with chronic pain.

Study Selection
Methodological elements were identified through review of the "Initiative on Methods, Measurement, and Pain Assessment in Clinical Trials" publications, selective literature searches, review of relevant references from articles critically assessing methodologies, and the authors' experience appraising RCTs with chronic pain outcomes.

The systematic review selected studies for measuring longitudinal change in pain, measuring the MCID against an external criterion, and including patients with chronic pain. A total of 17 studies met selection criteria; 11 reported on the MCID using the numerical rating scale (NRS) to measure pain and 7 used the visual analog scale (VAS). Most studies selected patients with chronic musculoskeletal pain, and a few also included patients with postherpetic neuralgia and diabetic peripheral neuropathy.

Main Results
Eighteen important methodological elements (see Table) related to measuring and reporting chronic pain outcomes in RCTs were identified in five categories: 1) pain intensity scale and assessment of pain; 2) quality of life; 3) global patient assessment of improvement; 4) data analysis; 5) results and conclusions.

Overall in the systematic review of both NRS and VAS studies, there was a high degree of methodological heterogeneity precluding comparisons across studies. The pain states rated were either not described or varied in the activity, span of time and whether extreme or average intensity was of interest. More importantly, there was large variation in the manner external criterion scales were used to define clinically significant change in estimating the MCID. Therefore, it was not possible from this evidence to define an MCID for reporting trial results of chronic pain.

Table.  Methodological Elements Related to Measuring and Reporting Chronic Pain Outcomes in RCTs by Category

Author's Conclusions and Comments
Defining the effectiveness of interventions ameliorating pain and its consequences poses challenges in designing, conducting, analyzing, and reporting of RCTs. Critically appraising these RCTs presents similar challenges. Owing to some unique aspects of chronic pain outcomes, methodological issues are encountered that do not always allow straightforward interpretation. Furthermore, methods used to define the MCID in chronic pain and estimates derived vary considerably. Due to heterogeneity in methods, the body of evidence does not permit conclusions about the clinically significant magnitude of change in NRS- or VAS-assessed pain among chronic pain patients. A range of MCIDs for chronic pain may be more plausible than a single consistent value across severity and causes of pain.

Because of the unique characteristics of chronic pain, it is important to approach appraisal of evidence from a context not always encountered in other settings. Making assumptions explicit and addressing the potentially problematic aspects of RCTs having chronic pain outcomes, especially the MCID, can facilitate better critical appraisal of intervention effectiveness. 

TEC Assessment Index

KEYWORDS: Orthopedics/PainManagement (category); SpecialReports (category); acute; AMP; amputation; ankylosing spondylitis; assessment; change; chronic; chronic low back pain; CLBP; curve; diabetic peripheral neuropathy; disease-modifying antirheumatic drugs; DMARD; DPN; elements; fibromyalgia; global assessment; global patient assessment of improvement; heterogeneity;; IMMPACT group; Initiative on Methods, Measurement, and Pain Assessment in Clinical Trials; LBP; longitudinal; low back pain; MCID; mean; median; methodological; methods; minimal clinically important difference; musculoskeletal; neuralgia; NRS; numeric rating scale; osteoarthritis; pain; pain intensity scale; percent change; PHN; physical therapy; postherpetic; problematic; PT; QoL; quality of life; receiver operating characteristic; responder criteria; rheumatoid arthritis; ROC; SALBP; SCT; SDD; SEM; sensitivity; smallest detectable difference; specificity; standard error of the measurement; stratified central tendency; subacute low back pain; subjective; VAS; visual analog scale; visual analogue scale;