Diagnostic epidural opioid blockade in primary fibromyalgia at rest and during exercise

Nine patients with primary fibromyalgia participated. The patients were studied prior to, during and immediately after 4 identical periods of exercise (bicycle ergometer) each performed 30 min after injection with saline, repeated saline, an opioid and naloxone. All substances were given epidurally, except for naloxone which was given intravenously. Finally, with the patients resting in bed, lignocaine was injected epidurally. Physiological variables, general exertion, dyspnoea, lower extremity exhaustion, pain and tender points in the lower half of the body were examined. Resting pain and tender points diminished significantly after the opioid injection. Lignocaine completely abolished resting pain and tender points. Lower extremity exhaustion was reduced by the opioid. General exertion and dyspnoea were unaffected by the opioid. In conclusion the results support the hypothesis that the pain in fibromyalgia is of peripheral nociceptive or spinal origin. We raise the hypothesis that the fatigability is, at least partly, due to inhibition because of pain.