Imagined Examples of Painful Experiences Provided by Chronic Low Back Pain Patients and Attributed a Pain Numerical Rating Score.

OBJECTIVE: The pain numerical rating scale (NRS) is widely used in pain research and clinical settings to represent pain intensity. For an individual with chronic pain, NRS reporting requires representation of a complex subjective state as a numeral. To evaluate the process of NRS reporting, this study examined the relationship between reported pain NRS levels and imagined painful events reported by study subjects. DESIGN: A total of 149 subjects with chronic low back pain characterized by the NIH Research Task Force Recommended Minimal Dataset reported current pain NRS and provided imagined examples of painful experiences also attributing to these an NRS. We present a quantitative and qualitative analysis of the 797 pain examples provided by the study subjects. RESULTS: Study subjects tended to be able to imagine both highly painful 10/10 events and non-painful events with relative agreement across subjects. While NRS for the pain examples tended to increase with example severity, for many types of examples there was wide dispersion around the mean pain level. Examination of pain examples indicated unexpected relationships between current pain and the intensity and nature of the imagined painful events. CONCLUSIONS: Our results indicate that the pain NRS does not provide a reliably interpretable assessment of current physical pain intensity for an individual with chronic pain at a specific moment.

Methadone-induced hypoglycemia.

To determine if recent observations of hypoglycemia in patients receiving high-dose methadone extended to an animal model, we explored the effects of methadone and other mu-opioids on blood glucose levels in mice. Methadone lowered blood glucose in a dose-dependent manner with 20 mg/kg yielding a nadir in average glucose levels to 55 ± 6 mg/dL from a baseline of 172 ± 7 mg/dL, an effect that was antagonized by naloxone and mu selective antagonists ß-funaltrexamine and naloxonazine. The effect was stereoselective and limited to only the l-isomer, while the d-isomer was ineffective. Despite the robust decrease in blood glucose produced by methadone, a series of other mu-opioids, including morphine, fentanyl, levorphanol, oxycodone or morphine-6ß-glucuronide failed to lower blood glucose levels. Similar differences among mu-opioid agonists have been observed in other systems, suggesting the possible role of selected splice variants of the mu-opioid receptor gene Oprm1. This mouse model recapitulates our clinical observations and emphasizes the need to carefully monitor glucose levels when using high methadone doses, particularly intravenously, and the need for controlled clinical trials.