We frequently see national guidelines and insurance payer guidelines recommending the measurement of both pain and function in our patients with chronic pain. They want to see changes in both pain and function as a justification for approval or payment of our treatments – particularly in the case of prescribing opioids. In looking at many of the national guidelines, however, we find that the surveys recommended measuring “function” are actually measures that assess Pain Interference (the extent to which pain hinders engagement with physical, cognitive, emotional, cognitive, and recreational activities, as well as sleep and enjoyment in life). Physical Function, on the other hand, is defined as “a measure of the ability to carry out activities that require physical actions, ranging from self-care to more complex activities that require a combination of skills, often within a social context”.

Are these really measuring the same thing? This question grew out of many observations by the senior author (Mackey) in caring for his patients. He noted that there were frequently significant improvements across many domains of emotional functioning, fatigue, pain interference and sleep following his treatments. However, physical function would often not improve in a commensurate way unless it was specifically targeted. This led us to take on this project. We started with 3259 patients surveyed by CHOIR and took a subset of those that had at least three longitudinal follow-up points. We applied a parallel process latent growth curve model analysis that showed a weak, unidirectional relationship (beta=0.18) between average Physical Function scores and changes in Pain Interference over the course of 90 days of care, and no relationship between average Pain Interference scores and changes in PF across time. In summary, Pain Interference is a poor surrogate measure for Physical Function. From a national policy perspective, we are measuring the “right thing” in assessing physical function. It is also clear that we are measuring it the wrong way. Fortunately, there are relatively straightforward ways to fix this problem in future guideline revisions.

Karayannis NV, Sturgeon JA, Kao MC, Cooley C, Mackey S. Physical function and pain interference demonstrate poor longitudinal association in people living with chronic pain: A PROMIS investigation. Pain. 2017 Jun. DOI: 10.1097/j.pain.0000000000000881. PMID: 28221284