Descending antinociception and fibromyalgia

The hypothesis is discussed that a dysfunction of the descending antinocice ptive system may underly the pain of fibromyalgia. Data from animal experim entation show that an interruption of the system by spinal cord cooling lea ds to (1) increase in ongoing activity, (2) lowering in stimulation thresho ld, and (3) increase in response magnitude in nociceptive dorsal horn neuro ns. The influence of the descending system was stronger on the responses to input from deep nociceptors than to input from cutaneous nociceptors. If s imilar changes occur also in patients, an impairment of the tonicly active descending system should be followed by (1) spontaneous pain (ongoing activ ity), (2) tenderness (lowering in mechanical threshold), and (3) hyperalges ia (increased responses to noxious stimuli). These changes should affect ma inly deep pain, because the antinociceptive system influences predominantly input from deep nociceptors.