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SUDOSCAN in autoimmune
small fiber neuropathy

Trevino, Jorge A. M.D., Novak, Peter MD. Ph.D.
Article title: TS-HDS and FGFR3 Antibodies in Small Fiber Neuropathy and Dysautonomia.
Muscle Nerve. 2021 Apr 1

In this study JA Trevino and P Novak from Brigham and Women’s Hospital, Harvard Medical School, Boston, tested small fiber neuropathy (SFN) in idiopathic neuropathy population and explored the autoimmune etiology of this complication. Autoimmune SFN is a neuropathy where autoimmunity plays a causative role. According to one study, up to 19% of patients with idiopathic SFN may have underlying immunological abnormalities.

Antibodies to either trisulfated heparin disaccharide (anti-TS-HDS) or fibroblast growth factor receptor-3 (anti-FGFR3) have been found in patients with idiopathic sensory-predominant SFN suggesting that they may be useful markers of neural autoimmunity. TS-HDS/FGFR3 antibodies are present in patients with evidence of autonomic dysfunction.

This retrospective study aimed to describe the SFN and autonomic profile of patients with anti-TS-HDS and anti-FGFR3.

Small fiber neuropathy was defined as a combination of clinical signs suggestive of small fiber dysfunction and at least one of the following structural or functional variables: abnormal epidermal nerve fiber density (ENFD); abnormal sweat gland nerve fiber density (SGNFD); abnormal sudomotor testing using SUDOSCAN’s measures (the following normative values were used for ESC*/kg: hands ≥1.03μS/kg, feet ≥1.14 μS/kg).

(*) ESC: electrochemical skin conductance

322 patients were included in the study, abnormal ENFD was detected in 71.4%, abnormal ESC/kg (SUDOSCAN) in 63.3%, and abnormal SGNFD in 48.8% of patients.

Frequency of positive or negative Anti-FGFR3 was significantly different among patients with mixed SFN (abnormal ENFD and SGNFD; and combined functional-morphological SFN (Abnormal ENFD, SGNFD, ESC measured with SUDOSCAN)) (see table below).

Only mixed SFN definition segregated seropositive from seronegative patients for anti-FGFR3 but not for anti-TSHDS.

SUDOSCAN measures combined to skin biopsy could be a helpful test to diagnose immune small fiber neuropathy.

Skin biopsy results and antibody presence

Abbreviations: TS-HDS: Trisulfated heparin disaccharide antibody; FGFR3: Fibroblast growth factor
receptor 3 antibody; ENFD: Epidermal nerve fiber density; SGNFD: Sweat gland Nerve Fiber Density; ESC/kg: Electrochemical skin conductance adjusted for weight; +: abnormal results/positive antibody, -:
normal result/absent antibody.
Keywords: Small fiber neuropathy, autoimmune, TS-HDS, FGFR3, dysautonomia, ENFD, SGNFD, ESC, SUDOSCAN.