Translation of random painful stimuli into numerical responses in fibromyalgia and perioperative patients

Number-based assessment tools are used to evaluate pain perception in patients and determine the effect of pain management. The aim of this study was to determine the ability of chronic and acute pain patients to score their response to randomly applied noxious stimuli and assess the effect of opioid treatment. Thirty-seven healthy controls, 30 fibromyalgia patients, and 62 postoperative patients with acute pain received random heat pain (Hp) and electrical pain (Ep) stimuli. All subjects rated their pain on an 11-point numerical rating scale (NRS). The data were analyzed using a penalty score system, based on the assumption that stimuli of higher intensity are scored with a greater NRS, and stratified into cohorts corresponding to "good," "mediocre," and "poor" scoring. Healthy controls were well able to score pain with 73% (Hp) and 81% (Ep) of subjects classified into cohort "good." Fibromyalgia had a negative effect on scoring with 45% (Hp, P = 0.03 vs controls) and 67% (Ep) of patients in cohort "good." In controls, scoring deteriorated during opioid administration leaving just 40% (Hp, P = 0.015 vs baseline) and 70% (Ep) of subjects in the cohort "good." Similar observations were made in fibromyalgia patients (P = 0.02) but not in surgical patients with postoperative pain. Consistency to grade pain using an NRS is high in healthy volunteers but deteriorates in chronic pain and during opioid administration to volunteers and chronic pain patients but not to acute pain patients.