Autofluorescent Flavoprotein Imaging of Intraepidermal Nerve Fibers: a Pilot Study

Small fiber neuropathy (SFN) is a common disorder, which has a profound negative impact on quality of life because of severe neuropathic pain. To reliably establish a diagnosis of SFN is challenging, since neurological examination and nerve conduction studies are often normal. Autofluorescent flavoprotein imaging (AFI) is an optical method through which neuronal activity in the termination area of small nerve fibers in the spinal cord can be quantified. Since the epidermis also contains a high density of small nerve terminals and since the number of intraepidermal nerve fibers is greatly reduced in patients with SFN, our hypothesis is that AFI intensity is reduced in patients with SFN. To support this hypothesis, a pilot study is required in which the investigators first need to confirm the precision of AFI in the epidermis of the third finger of 10 healthy volunteers. Secondly, lidocaine/prilocaine cream will be used as a negative control. Finally, the AFI signal will be measured after application of a 8% capsaicin patch, through which (temporarily) a selective reduction of small nerve fibers can be induced, mimicking SFN. Using this experimental design, the investigators will be able to test the reliability and validity of AFI for capsaicin-induced small nerve fiber degeneration. This would be a significant step in developing an objective, rapid and non-invasive diagnostic tool to diagnose patients with SFN, which may also be utilized as a biomarker in studies that assess the efficacy of novel treatments for SFN.