Small Fiber Function May Be Linked to Fibromyalgia

Although fibromyalgia is clinically well characterized, the specific pathology has not yet been clarified. A recent study from Germany, appearing in the March 9 issue of Brain, suggests that impaired small fiber function may be related to the pain of fibromyalgia syndrome (FMS).¹

“In the last few years, there were hints of a possible involvement of the small nerve fibers in the pathology of FMS,” says lead author Nurcan Üçeyler, MD, from the department of neurology at the University of Würzburg. “Our group is specialized on small fiber assessment and we set out to systematically investigate this hypothesis.”

The researchers prospectively enrolled 25 patients with FMS into their case-control study. They examined small fiber function by quantitative sensory testing and pain-related evoked potentials. They obtained intraepidermal nerve fiber density and regenerating intraepidermal nerve fibers from skin-punch biopsies that were obtained from the lower leg and upper thigh. These were compared with age- and gender-matched controls with a diagnosis of unipolar depression without pain (n=10) and a group of healthy individuals.

Results Show Differences

Those with a diagnosis of FMS had increased scores in neuropathic pain questionnaires compared with both depression and control subjects (P<0.001 each). When compared to controls, FMS patients, but not those who were depressed, had impaired small fiber function with increased warm and cold detection thresholds (P<0.001). Pain-related evoked-potential testing found increased N1 latencies when the feet were stimulated (P<0.001) and reduced amplitudes of pain-related evoked potentials at the face, hands, and feet (P<0.001) versus both control and depressed participants.

Skin biopsy results told a similar tale. Total (P<0.001) and regenerating intraepidermal nerve fibers (P<0.01) at the lower leg and upper thigh were reduced in those with FMS compared to controls. There was also a reduction noted in unmyelinated nerve fiber bundles when compared to both healthy controls and those with a diagnosis of depression.

“Using three different but complementary methods, we showed for the first time that small fiber function and morphology is impaired in patients with FMS compared to patients with depression and healthy controls,” says Dr. Üçeyler. “In light of our findings, a new discussion is needed to see if FMS can now be classified as a neuropathic pain syndrome and accepted as a disease. Researchers now have a trace to follow in order to find the reason for small fiber damage and hopefully new ways to treat pain in FMS.”

The research was supported by intramural funds from the University of Würzburg.