LAUSR

Abstract Objectives: Up to 50% of small fiber neuropathy (SFN) cases are idiopathic, but novel antibodies to Trisulfated Heparin Disaccharide (TS-HDS) and fibroblast growth factor receptor 3 (FGFR-3) have been implicated in half of these cases; the role of anti-Plexin D1 is less clear. We aimed to clarify presentation and management of these patients. Methods: An 18-month retrospective analysis revealed 54 cases of cryptogenic SFN who had testing for the 3 autoantibodies. Demographics, clinical features, epidermal nerve fiber density, and Quantitative Sudomotor Axon Reflex Test results were analyzed. Intravenous immunoglobulin (IVIG) treatment response was assessed. Results: In total, 44.4% of patients had antibodies (62.5% TS-HDS, 29.2% FGFR-3, and 20.8% Plexin D1). Male patients were more likely to be FGFR-3 positive (P = 0.014). Facial involvement was more common in seropositive patients (P = 0.034), and patients with a higher Utah Early Neuropathy Scale score had a higher TS-HDS titer (P = 0.0469), but other clinical features were not significantly different. Seropositive patients trended toward a higher SFN screening list score (P = 0.16), abnormal Quantitative Sudomotor Axon Reflex Test (P = 0.052), and prior erroneous diagnosis (P = 0.19). In patients who completed IVIG, examinations and questionnaires improved and mean epidermal nerve fiber density increased by 297%. Conclusions: TS-HDS, FGFR-3, and Plexin D1 antibodies are present in a high proportion of cryptogenic SFN cases with more facial involvement, and greater disease severity is associated with higher antibody titers. They are often misdiagnosed but may respond subjectively and objectively to IVIG.