Outcomes in pain medicine: a brief review

Pain, and particularly chronic pain, is a difficult outcome to measure due to its subjective and multidimensional nature. The Institute of Medicine estimates that 100 million Americans have chronic pain with a cost exceeding half a trillion dollars per year. There is a pressing need to identify appropriate outcome measures to better select and evaluate treatment modalities for these patients. It is also important that we demonstrate an evidence basis for these decisions given the current practice standard. Appropriate selection and implementation of these outcome measures can help accomplish both goals. The purpose of this review is to explore the difficulties and opportunities unique to pain outcome measures. The scope of the problem and impetus for implementation of appropriate measures is initially discussed, followed by requisite evaluation criteria for any measurement instrument. The authors then review frequently employed tools for measuring pain outcomes ranging from univariable and single domain scales to multidimensional instruments. A discussion of possible behavioral and objective measures is pursued, as well as measures of statistical and treatment efficacy. The article closes with a review of recent and ongoing efforts to validate and standardize pain outcome measures and suggests directions for future clinical and research assessment.