Three important studies highlight how fibromyalgia found a evidence of have a small-fiber polyneuropathy. Anne Louise Oaklander and colleagues in a Chronic widespread pain, including fibromyalgia: a pathway for care developed by the British Pain Society. Br J Anaesth. 2014;112:16-24 compared 27 patients who had satisfied the American College of Rheumatology (ACR) criteria for fibromyalgia with 30 matched controls.
In all, 41% of skin biopsies from patients with fibromyalgia were diagnostic for small-fiber peripheral neuropathy or polyneuropathy, compared with 3% from controls.
In a second study, of Üçeyler N, Zeller D, Kahn AK, et al. Small fibre pathology in patients with fibromyalgia syndrome. Brain. 2013;136:1857-1867. 25 patients with fibromyalgia were compared with 10 patients with depression but no pain and a group of healthy controls.
To evaluate small nerve fibers, participants underwent quantitative sensory testing, pain-related evoked potentials, quantified intraepidermal nerve fiber density, and evaluation of regeneration of intraepidermal nerve fibers of the lower leg and upper thigh.
Compared with healthy controls and patients with depression, patients with a diagnosis of fibromyalgia had impaired small-fiber function.
Skin biopsy findings demonstrated that the total and regenerating intraepidermal nerve fibers of the lower leg and upper thigh were reduced in patients with fibromyalgia compared with controls.
A reduction in unmyelinated nerve fiber bundles was seen in patients with fibromyalgia vs depressed and control subjects.
The authors concluded that these results support the concept that fibromyalgia is a neuropathic problem.
In a third study, of Levine T, Presence of small fiber neuropathy in a cohort of patients with fibromyalgia. Arthritis Rheum. 2012;64(Suppl 10):969. 56 patients who had met the 2010 ACR diagnostic criteria for fibromyalgia underwent skin punch biopsies at the proximal and distal lower limb sites. In 61% of these biopsies, findings were consistent with small-fiber neuropathy.
These three studies show that a significant percentage of individuals who had a diagnosis of fibromyalgia in fact had findings consistent with a small-fiber polyneuropathy process. This does not mean that fibromyalgia is a neuropathic condition in all people. Fibromyalgia may well be a separate condition from small-fiber neuropathy. However, it also means that people who previously have been diagnosed as having fibromyalgia may, in fact, have a small-fiber neuropathy process.