Descending antinociception and fibromyalgia.

The hypothesis is discussed that a dysfunction of the descending antinociceptive system may underly the pain of fibromyalgia. Data from animal experimentation show that an interruption of the system by spinal cord cooling leads to (1) increase in ongoing activity, (2) lowering in stimulation threshold, and (3) increase in response magnitude in nociceptive dorsal horn neurons. The influence of the descending system was stronger on the responses to input from deep nociceptors than to input from cutaneous nociceptors. If similar changes occur also in patients, an impairment of the tonicly active descending system should be followed by (1) spontaneous pain (ongoing activity), (2) tenderness (lowering in mechanical threshold), and (3) hyperalgesia (increased responses to noxious stimuli). These changes should affect mainly deep pain, because the antinociceptive system influences predominantly input from deep nociceptors.