Pain intensity, muscle strength, static muscle endurance, pressure
pain threshold, and pain tolerance at tender points and
control points were assessed in 31 patients with fibromyalgia
(FM), before and after intravenous administration of morphine
(9 patients), lidocaine (11 patients), and ketamine (11
patients). The three different studies were double-blind and
placebo-controlled. The patients were classified as
placebo-responders, responders (decrease in pain intensity by
> 50%) and non-responders.
The morphine test did not show any significant changes.
The lidocaine test showed a pain decrease during and
after the infusion. The ketamine test showed a significant
reduction in pain intensity during and after the test period.
Tenderness at tender points decreased and endurance
increased significantly, while muscle strength remained
unchanged. The present results support the hypothesis
that the NMDA receptors are involved in pain mechanisms in
fibromyalgia. These findings also suggest that central
sensitization is present in FM and that tender points
represent secondary hyperalgesia.
Sorensen J, Bengtsson A, Backman E, Henriksson KG, Bengtsson M