Pain Measurement and Brain Activity: Will Neuroimages Replace Pain Ratings?

Abstract

Arguments made for the advantages of replacing pain ratings with brain imaging data include assumptions that pain ratings are less reliable and objective and that brain image data would greatly benefit the measurement of treatment efficacy. None of these assumptions are supported by available evidence. Self-report of pain is predictable and does not necessarily reflect unreliability or error. Since pain is defined as an experience, magnitudes of its dimensions can be estimated by well established methods, including those used to validate brain imaging of pain. Brain imaging helps to study pain mechanisms and might be used as proxy measures of pain in persons unable to provide verbal reports. Yet eliminating pain ratings or replacing them with neuroimaging data is misguided because brain images only help explain pain if they are used in conjunction with self-report. There is no ‘objective readout’ mechanism of pain (“pain thermometer”) that is unaffected by psychological factors. Benefits from including neuroimaging data might include increased understanding of underlying neural mechanisms of treatment efficacy, discovery of new treatment vectors, and support of conclusions derived from self-report. However, neither brain imaging nor self-report data are privileged over the other. The assumption that treatment efficacy is hampered by self-report has not been shown; there are a plethora of treatment studies showing that self-report is sensitive to treatment. Dismissal of patients’ self-reports (pain ratings) by brain imaging data is potentially harmful. The aim of replacing self-report with brain imaging data is misguided and has no scientific or philosophical foundation.

Test-Retest Reliability of Pain-Related Brain Activity in Healthy Controls Undergoing Experimental Thermal Pain

“…As emphasized by several authors, pain is a subjective experience, and its diagnosis should continue to rely on the patient’s report. 11,12,23,28,31,34 …”

“…However, studies have found high test-retest reliability of subjective pain ratings for both acute 4 and chronic 17 pain, whereas this information is lacking for pain neuroimaging. 28 The reliability of fMRI findings in the study of pain is essential to determine before potential translation of this technology to clinical practice, as reliability establishes the upper bound for validity.…”

“…19 It is important to note that an individual’s pain experience is not static over time, and pain intensity or unpleasantness can fluctuate. 28 However, the degree to which these pain ratings vary is predictable, and therefore does not represent error. 30 Although the experience of pain can vacillate over time, subjective pain measures have been shown to reliably capture an individual’s pain experience.…”

Test-retest reliability of pain-related functional brain connectivity compared with pain self-report

“…If a neural marker of pain is not altered with an individual’s change in pain ratings, the neural marker is not likely explaining all of the variance associated with the individual’s subjective experience of pain. Further, neural pain markers are typically validated against self-reported pain, which in turn acts as an upper limit for the psychometric properties of neuroimaging results [27]. …”

Multivariate decoding of cerebral blood flow measures in a clinical model of on‐going postsurgical pain

“…This reliance on self-report to record individuals' pain experiences is understandable given the absence of a known biological index of pain. Improving pain phenotyping and developing more sensitive measurement techniques should add value to self-report [Robinson et al, 2013]. Ideally such new methods would also provide robust, individualized predictions of treatment response [Rosa and Seymour, 2014; Woodcock et al, 2007].…”