Do Small Fiber Neuropathies Cause Fibromyalgia?

Nerve fibersFibromyalgia syndrome (FM) is a chronic pain condition that is associated with abnormal pain sensitivity, mood disturbances, and fatigue. Despite everything we know about FM, its cause and pathophysiology are not fully understood. However, we do know that individuals with FM have dysfunctional pain modulation, specifically decreased pain inhibition. With this in mind, several research teams sought to determine whether FM participants had peripheral neuropathies that may contribute to their chronic pain.

First, a research group in Germany wanted to see if peripheral neuropathology did indeed exist in FM participants. They recruited 25 FM participants for neurophysiological assessments and quantitative sensory testing. The skin of participants’ lower legs and upper thighs were biopsied to determine the density of nerve fibers in these regions. Participants with FM were found to have impaired small fiber function with abnormally increased cold and warm detection thresholds, when compared to control subjects. Furthermore, the skin biopsies showed that FM participants had fewer nerve fibers in both biopsied regions.1 Thus, this study supports the idea that some individuals with FM have impaired small fiber function and potential neuropathic origins to their pain.

Another research team (from Harvard University) compared symptoms of FM to those of small-fiber polyneuropathy (SFPN). SFPN causes similar symptoms as FMS, but is caused by degeneration of peripheral small fiber neurons. Because of the similarity in symptoms of FM and SFNP patients, this research team wanted to see if some patients diagnosed with FM have unrecognized SFPN. Thus, the researchers analyzed pathological and phyisiological markers in 27 FM participants. Skin biopsies were also taken of the leg. It was found that 41% of skin biopsies of FM participants were consistent with SFPN.2 These restults indicate that some patients with FM may have undiagnosed SFPN, which has objective testing methods and can be treated definitively.                                                                        
In conclusion, while these finding point to an important role of the peripheral nervous system for FM symptoms, more research needs to be done to determine the relationship between small fiber neuropathies and FM. At the Center for Musculoskeletal Pain Research, we are also evaluating the role of peripheral tissues for FM pain. We think that more insight into the role of small fiber neuropathies in FM could lead to better treatment and diagnostic techniques in the future.

Meriem Mokhtech, BS
Senior Laboratory Technician
UF Center for Musculoskeletal Pain Research

1. Uceyler N, Zeller D, Kahn AK, Kewenig S, Kittel-Schneider S, Schmid A, Casanova-Molla J,Reiners K, Sommer K. Small fibre pathology in patients with fibromyalgia syndrome. Brain 2013; 136; 1857–1867.
2. Oaklander AL, Herzog ZD, Downs H, Klein MM. Objective evidence that small-fiber polyneuropathy underlies some illnesses currently labeled as fibromyalgia. Pain 2013;