Researchers Provide Insight into the Effects of Using Opioids to Treat Chronic Pain

A poster session at the 2013 AAPM annual meeting highlighted research on the role of central sensitization in chronic pain, the use of microwave ablation to treat refractory pain in patients with soft tissue tumors, a possible treatment for opioid-induced hyperalgesia, and the psychosocial effects of opioid treatment in patients with sickle-cell anemia.

Central sensitization as a contributing factor to many pain conditions, the use of microwave ablation to treat bone and soft tissue tumors, the impact of opioid use on biopsychosocial-spiritual function in sickle cell anemia, and the anti-hyperalgesic effects of dexmedetomidine on opioid-induced hyperalgesia (OIH) were the focus of a plenary session moderated by James C. Watson, MD, of the Mayo Clinic in Rochester, MN, during the 2013 American Academy of Pain Medicine annual meeting, being held April 12-14 in Fort Lauderdale, FL.

During the plenary session, Brittney R. Reyes, BA, of Stanford University School of Medicine in San Francisco, CA, discussed the results of a study that provided insight into central sensitization as a contributing factor to chronic pain conditions. In the study, the investigators used resting state functional magnetic resonance imaging (fMRI) to image central sensitization in the human spinal cord. The investigators evaluated 16 patients that were randomized into two groups: non-sensitized and sensitized. Sensitized patients had their left forearm sensitized using the heat capsaicin model for central sensitization. Non-sensitized patients had no capsaicin applied. The researchers used fMRI to take a heat pain scan (to functionally define the dorsal horn) and a resting state scan.

The investigators found increased functional connectivity in the spinal cord of sensitized patients with no pain compared to patients who did not undergo sensitization. These results suggest that central sensitization at the level of the spinal cord occurs, even in the absence of perceived of pain. Going forward, the investigators would like to translate these findings into a clinical population and use resting fMRI to detect locations of peripheral lesions.

Also, during the session,. Adrian Kastler, MD, of Centre Hospitalier Universitaire, Besançon, in Franche Comté, France, discussed the use of microwave ablation (MWA) under local anesthesia in patients with bone and soft tissue tumors. In this retrospective analysis of 15 patients, the investigators assessed the feasibility, safety, and efficacy of MWA for the management of refractory pain in patients with bone and soft tissue tumors. All MWA procedures were performed in combination with CT guidance under local anesthesia and nitrous oxide.

The investigators found that immediate pain relief was greater than or equal to 50 percent in most patients, lasting for an average of 4.36 months. However, one patient experienced a major complication associated with MWA, as this was the first case performed and the intensity and duration of MWA was too long and high. No additional cases have been identified to date, as that duration and intensity of treatment was not used.

Overall, Kastler noted that MWA is a safe and feasible approach that can be used under local anesthesia and appears to be simpler and faster than other ablative approaches such as radiofrequency ablation (RFA). In addition, the approach uses electromagnetic waves that can treat larger areas, and the ablation time seems shorter than RFA. In conclusion, MWA treatment appears to be a feasible and effective approach for the management of pain in patients with bone and soft-tissue tumors.

Another presentation given by Yeon-Dong Kim, MD, of Wonkwang University Hospital in Iksan, North Jeolla, South Korea, highlighted the anti-hyperalgesic effects of dexmedetomidine on high-dose remifentanil-induced hyperalgesia. It is understood that dexmedetomidine is a highly selective a2 adrenergic agonist that reduces the intensity of opioid-induced hyperalgesia (OIH). Ninety patients who underwent laparoscopically assisted vaginal hysterectomy (LAVH) were randomized to three groups that received dexmedetomidine, saline, and/or remifentanil. While the investigators found that high-dose remifentanil induced hyperalgesia, dexmedetomidine effectively reduced those symptoms.

Patients treated with dexmedetomidine reported less pain, used less post-surgical morphine, and went longer before requesting medication for pain relief than patients treated with placebo. They also reported fewer adverse opioid-related effects, including nausea. Kim concluded that dexmedetomidine might serve as a viable option for the treatment of OIH.

In the final presentation of the session, Abdulkhaliq J. Alsalman, MS, of Virginia Commonwealth University in Richmond, discussed the biopsychosocial and spiritual effects of prescription opioid use in patients with sickle cell anemia (SCA). In this multiphase, mixed-method study, the investigators evaluated 21 African-American patients with SCA and used a grounded theory approach to analyze the data.

Based on the responses patients gave during interviews, researchers classified opioid use as having a positive or negative effect on patients’ biological, psychological, social, spiritual, and “miscellaneous” life functions.

Positive effects included feeling good about a pain free life and avoidance of pity or sympathy. However, negative effects included guilt, isolation, dependency on others, decreased cognitive ability, fear of consequences, and resentment toward healthcare providers. Patients reported “divergent” effects (not uniformly positive or negative) on relationships, productivity in school or work, mood, social and spiritual commitments, outlook, and demeanor.

According to the study authors, analysis of the data revealed “divergent effects of prescribed opioids in various domains among SCD patients, which likely modulate subsequent opioid taking behavior… In all types of effects, biological effects appeared to be mediators of more indirect effects which led to alterations in subsequent opioid taking behavior.”

Based on these results, the research team is “the team is building and validating a quantitative survey that catalogs the above effects, with the goal of an adequate appreciation of the various consequences of prescribed opioids. The quantification of effects is expected to help guide prescribing decisions and rigorous testing of new hypotheses that may challenge current models of opioid-taking behavior,” according to a news release announcing the study results.