Many studies showed that most patients with fibromyalgia have a small-fibre loss, as assessed with skin biopsy. However how this skin biopsy abnormality affects small-fibre function and whether this abnormality is the leading cause underlying the widespread pain of fibromyalgia are still issues of controversy. In this case-control study we aim at identifying how the small-fibre loss in patients with fibromyalgia affects sensory and autonomic small-fibre function, and whether the small-fibre function abnormalities resemble those of small-fibre neuropathy due to established aetiologies.
We will use skin biopsy for identifying small-fibre loss in patients with fibromyalgia and in patients with small-fibre neuropathies due to diabetes and autoimmune disease. We will investigate Quantitative Sensory Testing (QST) for assessing sensory small-fibre function, the Dynamic Sweating Test (DST) for assessing autonomic small-fibre function. We will also collect clinical and laboratory variables including the serum brain-derived neurotrophic factor (BDNF), commonly considered a marker of neuroplasticity in patients with peripheral nerve damage and pain.
We will compare skin biopsy, QST, DST and BDNF findings between patients with fibromyalgia, patients with small-fibre neuropathies and healthy subjects. This comparison will allow testing how the small-fibre loss affects sensory and autonomic function in patients with fibromyalgia, whether QST, DST abnormalities and BDNF level resemble those in patients with small-fibre neuropathies due to diabetes and autoimmune diseases. We will also correlate the BDNF serum levels with the different variables collected in patients with fibromyalgia and patients with small-fibre neuropathy.
Our findings may eventually settle whether fibromyalgia should be regarded as a small-fibre neuropathy, and possibly identify whether serum BDNF might be used as a biomarker of small-fibre damage in patients with fibromyalgia.
Our study aims at assessing how small-fibre loss in patients with fibromyalgia is associated with clinically significant abnormalities of small-fibre function and pain, and whether these abnormalities resemble those of patients with small-fibre neuropathy due to well-established condition. Our study also seeks whether serum level of BDNF differs across the three sample of subjects (patients with fibromyalgia, patients with small-fibre neuropathy and healthy participants). Similarities in small-fibre function and serum level of BDNF between patients with small-fibre loss due to fibromyalgia and small-fibre neuropathy due to diabetes and autoimmune diseases may call for a change in the way we classify patients with fibromyalgia.
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