Clinical Importance of Changes in Chronic Pain Intensity Measured on an 11-point Numerical Pain Rating Scale

Pain. 2001 Nov;94(2):149-58. doi: 10.1016/s0304-3959(01)00349-9.

Abstract

Pain intensity is frequently measured on an 11-point pain intensity numerical rating scale (PI-NRS), where 0=no pain and 10=worst possible pain. However, it is difficult to interpret the clinical importance of changes from baseline on this scale (such as a 1- or 2-point change). To date, there are no data driven estimates for clinically important differences in pain intensity scales used for chronic pain studies. We have estimated a clinically important difference on this scale by relating it to global assessments of change in multiple studies of chronic pain. Data on 2724 subjects from 10 recently completed placebo-controlled clinical trials of pregabalin in diabetic neuropathy, postherpetic neuralgia, chronic low back pain, fibromyalgia, and osteoarthritis were used. The studies had similar designs and measurement instruments, including the PI-NRS, collected in a daily diary, and the standard seven-point patient global impression of change (PGIC), collected at the endpoint. The changes in the PI-NRS from baseline to the endpoint were compared to the PGIC for each subject. Categories of "much improved" and "very much improved" were used as determinants of a clinically important difference and the relationship to the PI-NRS was explored using graphs, box plots, and sensitivity/specificity analyses. A consistent relationship between the change in PI-NRS and the PGIC was demonstrated regardless of study, disease type, age, sex, study result, or treatment group. On average, a reduction of approximately two points or a reduction of approximately 30% in the PI-NRS represented a clinically important difference. The relationship between percent change and the PGIC was also consistent regardless of baseline pain, while higher baseline scores required larger raw changes to represent a clinically important difference. The application of these results to future studies may provide a standard definition of clinically important improvement in clinical trials of chronic pain therapies. Use of a standard outcome across chronic pain studies would greatly enhance the comparability, validity, and clinical applicability of these studies.

Publication types

  • Clinical Trial
  • Controlled Clinical Trial
  • Multicenter Study

MeSH terms

  • Adult
  • Aged
  • Aged, 80 and over
  • Anticonvulsants / therapeutic use
  • Chronic Disease
  • Controlled Clinical Trials as Topic / methods
  • Controlled Clinical Trials as Topic / standards
  • Female
  • Fibromyalgia / diagnosis
  • Fibromyalgia / drug therapy
  • Humans
  • Low Back Pain / diagnosis
  • Low Back Pain / drug therapy*
  • Male
  • Middle Aged
  • Neuralgia / diagnosis
  • Neuralgia / drug therapy
  • Osteoarthritis / diagnosis
  • Osteoarthritis / drug therapy
  • Pain Measurement / standards*
  • Pregabalin
  • Treatment Outcome
  • gamma-Aminobutyric Acid / analogs & derivatives*
  • gamma-Aminobutyric Acid / therapeutic use*

Substances

  • Anticonvulsants
  • Pregabalin
  • gamma-Aminobutyric Acid