Editor's comment: This study compared the small nerve fibers of fibromyalgia patients with those of people with depression who don't have FM and with healthy controls. The researchers found that impaired small nerve fibers were found only in the people with fibromyalgia. Based on this study, the American Psychiatric Association published an article titled, “New Findings Suggest Fibromyalgia Is Neuropathic, Not Depression Variant.” The article quoted the study authors saying, "This strengthens the notion that fibromyalgia syndrome is not a variant of depression, but rather represents an independent entity that may be associated with depressive symptoms," the researchers said. Furthermore, the findings point "towards a neuropathic nature of pain in fibromyalgia syndrome."
Small fibre pathology in patients with fibromyalgia syndrome.
By Nurcan Üçeyler, et al.
Fibromyalgia syndrome is a clinically well-characterized chronic pain condition of high socio-economic impact. Although the pathophysiology is still unclear, there is increasing evidence for nervous system dysfunction in patients with fibromyalgia syndrome.
In this case-control study we investigated function and morphology of small nerve fibres in 25 patients with fibromyalgia syndrome. Patients underwent comprehensive neurological and neurophysiological assessment. We examined small fibre function by quantitative sensory testing and pain-related evoked potentials, and quantified intraepidermal nerve fibre density and regenerating intraepidermal nerve fibres in skin punch biopsies of the lower leg and upper thigh.
The results were compared with data from 10 patients with monopolar depression without pain and with healthy control subjects matched for age and gender.
Neurological and standard neurophysiological examination was normal in all patients, excluding large fibre polyneuropathy.
Patients with fibromyalgia syndrome had increased scores in neuropathic pain questionnaires compared with patients with depression and with control subjects (P < 0.001 each).
Compared with control subjects, patients with fibromyalgia syndrome but not patients with depression had impaired small fibre function with increased cold and warm detection thresholds in quantitative sensory testing (P < 0.001).
Investigation of pain-related evoked potentials revealed increased N1 latencies upon stimulation at the feet (P < 0.001) and reduced amplitudes of pain-related evoked potentials upon stimulation of face, hands and feet (P < 0.001) in patients with fibromyalgia syndrome compared to patients with depression and to control subjects, indicating abnormalities of small fibres or their central afferents.
In skin biopsies total (P < 0.001) and regenerating intraepidermal nerve fibres (P < 0.01) at the lower leg and upper thigh were reduced in patients with fibromyalgia syndrome compared with control subjects.
Accordingly, a reduction in dermal unmyelinated nerve fibre bundles was found in skin samples of patients with fibromyalgia syndrome compared with patients with depression and with healthy control subjects, whereas myelinated nerve fibres were spared.
All three methods used support the concept of impaired small fibre function in patients with fibromyalgia syndrome, pointing towards a neuropathic nature of pain in fibromyalgia syndrome.
Source: Brain, June 2013. By Nurcan Üçeyler, Daniel Zeller, Ann-Kathrin Kahn, Susanne Kewenig, Sarah Kittel-Schneider, Annina Schmid, Jordi Casanova-Molla, Karlheinz Reiners and Claudia Sommer. Department of Neurology, University of Würzburg, 97080 Würzburg, Germany.