Small fiber neuropathy detected among patients with fibromyalgia

WASHINGTON — A majority of patients with fibromyalgia and neuropathic pain were diagnosed with small fiber neuropathy based on reduced epidermal nerve fiber, according to research presented at the American College of Rheumatology Annual Meeting.

Researchers retrospectively examined 56 patients who met either the ACR criteria or the 2010 revised fibromyalgia criteria. Punch biopsies were performed at proximal and distal sites on patients’ lower limbs. Epidermal nerve fiber density was counted on 50 micron sections, and PGP 9.5 immunolabeling was performed.

“A significant percentage of patients with fibromyalgia will often have neuropathic complaints, so in addition to the kind of dull muscle, flu-like symptoms, they will get burning, stabbing, tingling [and] allodynia,” researcher Todd D. Levine, MD, assistant professor at the University of Arizona, told Healio.com. “Some of them will have autonomic systems. All of that is suggestive that there might be a neuropathic component to their disorder.

“Despite that, if you do traditional EMG/nerve conduction studies, those are normal. One of the reasons we think that it is normal is that the pain fibers … are very small fibers. They’re too small to be detected by the standard tests. So, this technique, which involves a small 3-mm punch biopsy, allows us to study these small unmyelinated nerve fibers in patients.”

A standard serologic evaluation searched for identifiable causes for neuropathy in patients with reduced epidermal nerve fiber density, resulting in 61% of patients being diagnosed with small fiber neuropathy. Five patients displayed evidence of neuropathy on EMG/nerve conduction studies that was inconclusive for diagnosis.

Of the patients with fibromyalgia and small fiber neuropathy, 71% had serologic evidence of underlying etiology for the neuropathy, which had been undetected previously and most of which was treatable. Identifiable causes of small fiber neuropathy among patients included glucose metabolism (n=11), vitamin D deficiency (n=5), Sjögren’s syndrome (n=2) and elevated erythrocyte sedimentation rate (n=2).

“This would argue that at least in some of the patients, the pain generator may be the small nerves, as opposed to being in the brain, where some people think the pain is,” Levine said. “Probably it’s going to be a combination of both, so that fibromyalgia is really, probably a combination of pathophysiologies.”

Disclosure: Levine and researcher David Saperstein, MD, reported ownership or partnership in Corinthian Reference Labs.

For more information:

Levine TD. P969: Presence of Small Fiber Neuropathy in a Cohort of Patients with Fibromyalgia. Presented at: American College of Rheumatology 2012 Annual Meeting; Nov. 10-14, Washington.