Assessment of Small Fiber Neuropathy in Rare Diseases Using Sudoscan

Small fiber polyneuropathy (SFPN) is diagnosed through a combination of symptoms, signs and confirmatory diagnostic testing. Nerve conduction studies are not sensitive enough in most of the cases leaving the ankle skin biopsy with measurement of intraepidermal nerve fiber density (IENFD) as the main diagnostic tool. Despite its utility and reproducibility, skin biopsy is invasive, expensive and requires a central laboratory for processing and interpretation. Quantitative sudomotor axon reflex testing (QSART) is also routinely used for evaluation of small fiber neuropathy as sudomotor axons can also be involved. This test however remains technically challenging and requires testing conditions in specialized labs that are not always suitable for all patients' population. By comparing findings on skin biopsy and/or QSRT, accepted gold standard for diagnosing SFPN, the investigators seek to find faster, less-invasive ways to diagnose and monitor small-fiber polyneuropathy in rare diseases using Sudoscan measurement.