• Yi Zhang, Shihab Ahmed, Trang Vo, Kristin St Hilaire, Mary Houghton, Abigail S Cohen, Jianren Mao, and Lucy Chen.
• MGH Center for Translational Pain Research, Department of Anesthesia, Critical Care and Pain Medicine, Massachusetts General Hospital, Harvard Medical School, Boston, Massachusetts, USA.
• Pain Med. 2015 May 1;16(5):911-22.

ObjectiveThe aim of this study was to compare the sensitivity to experimental pain of chronic pain patients on opioid therapy vs chronic pain patients on non-opioid therapy and healthy subjects by quantitative sensory testing (QST).SettingThere is a growing body of evidence demonstrating that chronic use of opioid drugs may alter pain sensitivity. Identifying the characteristic changes in thermal pain sensitivity in chronic opioid users will be helpful in diagnosing pain sensitivity alterations associated with chronic opioid use.MethodsUtilizing an office-based QST technique, we examined thermal pain threshold, tolerance, and temporal summation in 172 chronic pain subjects receiving opioid therapy, 121 chronic pain subjects receiving non-opioid therapy, and 129 healthy subjects.ResultsIn chronic pain subjects receiving opioid therapy, there were detectable differences in QST characteristics compared with both chronic pain subjects receiving non-opioid therapy and healthy subjects. Specifically, in chronic pain subjects receiving opioid therapy, 1) sensitivity to heat pain was increased; threshold to heat pain was significantly lower; 2) tolerance to supra-threshold heat pain was significantly decreased; and 3) temporal pain summation was exacerbated, as compared with chronic pain subjects receiving non-opioid therapy. In a subgroup of chronic pain subjects receiving opioid therapy with increased heat pain sensitivity, their average opioid medication dosage was significantly higher than those who had an above-average heat pain threshold. Moreover, a subset of chronic pain subjects on opioid therapy exhibited a significant decrease in diffuse noxious inhibitory control (DNIC) compared with chronic pain subjects on non-opioid therapy.ConclusionThese findings suggest that a subset of QST parameters can reflect opioid-associated thermal pain sensitivity alteration, including decreased heat pain threshold, decreased cold and heat pain tolerance, diminished DNIC, and/or exacerbated temporal summation.© 2014 American Academy of Pain Medicine.

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