(HealthDay News) – Some patients diagnosed with fibromyalgia may actually have small-fiber polyneuropathy (SFPN), according to a study published online June 7 in PAIN.

Anne Louise Oaklander, MD, PhD, from Harvard Medical School in Boston, and colleagues analyzed SFPN-associated symptoms, signs, and pathological and physiological markers in 27 patients with fibromyalgia (who satisfied the American College of Rheumatology criteria and had documented evidence of a physician’s diagnosis) and in 30 normal matched controls.

The researchers found that 41% of distal-leg neurodiagnostic skin biopsies from subjects with fibromyalgia and 3% from controls were diagnostic for SFPN. Compared with controls, patients with fibromyalgia had significantly higher Michigan Neuropathy Screening Instrument and Utah Early Neuropathy Scale scores. The prevalence of abnormal autonomic-function testing was equal between the groups. Glucose tolerance tests were normal from 13 subjects with fibromyalgia and SFPN-diagnostic biopsies, but eight, two, and one patient, respectively, had dysimmune markers, hepatitis C serologies, and apparent genetic causality.

“These findings suggest that some patients with chronic pain labeled as fibromyalgia have unrecognized SFPN, a distinct disease that can be tested for objectively and sometimes treated definitively,” the authors write.

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