The Clinical Importance of Changes in the 0 to 10 Numeric Rating Scale for Worst, Least, and Average Pain Intensity: Analyses of Data From Clinical Trials of Duloxetine in Pain Disorders

J Pain. 2010 Feb;11(2):109-18. doi: 10.1016/j.jpain.2009.06.007. Epub 2009 Aug 8.

Abstract

Data on 1,700 patients pooled from 5 randomized, placebo-controlled duloxetine studies (3 in diabetic peripheral neuropathic pain and 2 in fibromyalgia) were analyzed to determine clinically important differences (CIDs) in the 0 to 10 Numeric Rating Scale-Pain Intensity (NRS-PI) for patient-reported "worst" and "least" pain intensity while validating the previously published level for "average" pain. The correspondence between the baseline-to-endpoint raw and percentage change in the NRS-PI for the worst, least, and average pain were compared to patients' perceived improvements at endpoint as measured by the 7-point Patient Global Impression of Improvement (PGI-I) scales. Stratification by baseline pain separated the raw but not the percent change scores. The PGI-I category of "much better" or above was our a priori definition of a CID. Cutoff points for the NRS-PI change scores were determined using a receiver operator curve analysis. A consistent relationship between the worst and average NRS-PI percent change and the PGI-I was demonstrated regardless of the study, pain type, age, sex, or treatment group with a reduction of approximately 34%. The least pain item CID was slightly higher at 41%. Raw change CID cutoff points were approximately -2, -2.5 and -3 for least, average, and worst pain respectively.

Perspective: We determined an anchor-based value for the change in the worst, least, and average pain intensity items of the Brief Pain Inventory that best represents a clinically important difference. Our findings support a standard definition of a clinically important difference in clinical trials of chronic-pain therapies.

MeSH terms

  • Adrenergic Uptake Inhibitors / therapeutic use*
  • Aged
  • Disability Evaluation
  • Double-Blind Method
  • Duloxetine Hydrochloride
  • Female
  • Fibromyalgia / drug therapy
  • Humans
  • Male
  • Mathematics*
  • Middle Aged
  • Outcome Assessment, Health Care
  • Pain Measurement / methods*
  • ROC Curve
  • Randomized Controlled Trials as Topic
  • Severity of Illness Index
  • Somatoform Disorders / drug therapy*
  • Thiophenes / therapeutic use*
  • Treatment Outcome

Substances

  • Adrenergic Uptake Inhibitors
  • Thiophenes
  • Duloxetine Hydrochloride