Quantitative sensory testing in nociplastic pain: what should we be looking for and what does it tell us?

The Perspectives manuscript by Clark and Yang1 hypothesizes that some individuals with primary nociplastic pain present with (nondermatomal) sensory loss, rather than exclusively sensory gains, and that this feature should be included in the new definition(s) for nociplastic pain. They posit that this would reduce the number of individuals with chronic pain that are unclassified using current nociplastic pain criteria. The manuscript is very well written and makes many points that should be considered and further studied. Although quantitative sensory testing (QST) has a long history of use in the pain field, the authors must acknowledge the significant limitations of this method in light of the accumulated data. Even in the prototypical nociplastic pain condition fibromyalgia (FM), QST measures are often normal. Between 30% and 70% of individuals with the clinical diagnosis of FM lack evidence of central sensitization on QST (decreased mechanical or thermal threshold).2,3,6 Dynamic QST measures such as those assessing temporal summation or conditioned pain modulation perform are even less discriminative, with recent studies suggesting that these are often not significantly different in FM patients compared with healthy controls.5,8 In light of this, it is clear that the new definition(s) for nociplastic pain must acknowledge that identifying hyperalgesia or allodynia on QST is helpful, but should not be required to make this diagnosis. It is possible that newer QST measures that probe for multisensory sensitivity to light or noises may be more discriminative than legacy QST measures,4,7 but more studies need to incorporate these measures to better understand their utility. Clark and Yang cite many studies showing that subsets of individuals with nociplastic pain condition such as fibromyalgia have decreases in sensation, both by self-report and with QST testing. Thus it is likely true that if this feature was added to the diagnostic criteria for nociplastic pain, far fewer individuals would be “unclassifiable,” as now occurs when QST evidence of central sensitization is required. However, they also point out that similar sensory deficits have been identified in many nonpain conditions, so it is unlikely that the finding of sensory deficits would be specific for nociplastic pain. Because there is no gold standard for nociplastic pain, the authors simply do not know whether this approach of adding loss of sensation makes scientific sense. Where do the authors go from here? The authors conclude that we simply need more research in this area can be agreed to by all. Quantitative sensory testing is not simple to perform well, and when incorporated into research or practice, it adds significant participant/patient burden and expense. Is the juice worth the squeeze or can some of these measures be eliminated in some new pain studies, now that we better understand what the measures do—and do not—tell us? Conflict of interest statement D.J. Clauw has served as a Consultant for Pfizer, Lilly, Tonix, Lundbeck, Virios, Swing, Neurometrix, Merck, Axsome and has testified against opioid manufacturers in State of Oklahoma, Florida, and has testified in litigation in defense of breast implant manufacturers and vaccine manufacturers.