Pain relief through expectation in Fibromyalgia Syndrome patients

A team of Canadian researchers have found that, although positive expectations can affect the pain signals of people with Fibromyalgia Syndrome, they does not do so by influencing spinal activity in the same way as in healthy individuals.

In healthy adults, expectations can modulate pain signals, with an expectation of analgesia or pain-relief triggering descending inhibition, a response that mediates pain signals.

Since descending inhibition is known to be deficient in Fibromyalgia Syndrome patients, the researchers tested the possibility that expectancy-mediated analgesia would improve, or even kick-start, the deficient inhibitory responses of Fibromyalgia Syndrome patients.

By measuring subjective pain ratings, spinal withdrawal reflexes, and somatosensory evoked potentials (SEP), it was possible to test whether or not expectancy-mediated analgesia involved descending inhibition in Fibromyalgia Syndrome patients.

The researchers found that expectations of analgesia reduced subjective pain ratings and decreased SEP amplitudes, confirming that expectations influence thalamocortical processes.

However, even when analgesia was experienced, the spinal activity of Fibromyalgia Syndrome patients was abnormal, showing heightened reflex responses.

This demonstrates that, unlike with healthy subjects, the modulation of pain by expectations in people with Fibromyalgia Syndrome fails to influence spinal activity.

These results indicate that people with Fibromyalgia Syndrome are capable of expectancy-induced analgesia but that, for them, this form of analgesia does not depend on the recruitment of descending inhibitory projections.

References:

1. Goffaux P, de Souza JB, Potvin S, Marchand S. Pain relief through expectation supersedes descending inhibitory deficits in fibromyalgia patients. Pain. 2009 Jun 11. [Epub ahead of print]