The evidence for central nervous system dysfunction in fibromyalgia is clear: the ascending pain producing pathways are overly activated, while the descending pain inhibitory pathways are under-activated. This results is people with fibromyalgia experiencing pain where no injury or sign of damage exists.
Problems with the peripheral nervous system in the body also exist. The nerve fibers that carry pain signals to the brain are overly activated, and some of the small, unmyelinated nerves in the skin and the eyes that carry sensory information to the spinal cord and brain are damaged in some patients.
The question researchers have been grappling with is whether these damaged nerves are contributing to the pain in fibromyalgia or if they are some sort of side process. The small nerve fiber damage in fibromyalgia is occurring in two ways; first, the small nerve fibers are disappearing, and those that are left are smaller in diameter than usual. The second issue is unusual, and has led researchers to call the small nerve problems in fibromyalgia “small nerve pathology” instead of “small fiber neuropathy”.