A negative correlation between hyperalgesia and analgesia in patients with chronic radicular pain: Is hydromorphone therapy a double-edged sword?

Background: Opioids are the cornerstone therapy for the treatment of moderate to severe pain. Yet, unconfirmed evidence suggests that chronic exposure to opioids may cause hypersensitivity to pain, a phenomenon known as opioid-induced hyperalgesia (OIH). Objectives: The current preliminary prospective study was aimed to explore the relationship between experimental OIH and clinical opioid induced analgesia (OIA) in a model of experimental OIH in patients with chronic radicular pain using intermediate-term opioid therapy. Study Design: Prospective evaluation Setting: Interdisciplinary Pain Clinic at a referral Health Care Campus Methods: Thirty patients with chronic neuropathic (radicular) pain were assessed prior to and following 4 weeks of an individually titrated dose of oral hydromorphone treatment (4-20 mg/d). The assessments included an evaluation of experimental OIH by testing for heat pain intensity and cold pain tolerance and an assessment of OIA by completing pain and disability questionnaires. Results: Hydromorphone was found to induce hyperalgesia, as measured by an elevation of phasic heat pain intensity (P < 0.05). At the same time, hydromorphone caused significant clinical analgesic effects. There was a notable reduction in average daily pain scores (primary analgesic outcome) of 26 Visual Analog Scale (0-100) points. A significant negative correlation was found between OIH and all OIA measures (r = -0.389, P < 0.05 for the primary analgesic outcome). Hydromorphone dosage was positively correlated with OIH (P < 0.01, r = 0.467) and negatively correlated with OIA parameters (r = -0.592, P < 0.01 for the primary analgesia outcome). Limitations: The nonrandomized, open-label, prospective evaluation. Conclusion: A 4-week regimen of open-label hydromorphone therapy results in a dosedependent OIH, which negatively correlates with its analgesic effect. Future randomized, controlled, and blinded studies are needed to verify these preliminary results.