A double-blind placebo-controlled pilot study of immunoglobulin for small fiber neuropathy associated with TS-HDS and FGFR-3 autoantibodies.

Introduction/aims: Small fiber neuropathies (SFN) have been associated with two autoantibodies, trisulfated heparin disaccharide (TS-HDS) and fibroblast growth factor receptor 3 (FGFR-3), and intravenous immune globulin (IVIG) has been suggested as a potential therapy. The study objective is to determine the efficacy of IVIG on nerve density, pain and neurologic examinations in patients with SFN associated with TS-HDS and FGFR-3 autoantibodies.

Methods: This was a double-blind placebo-controlled pilot study. Subjects with SFN confirmed by history, examination, and skin biopsy with elevated autoantibodies to TS-HDS and/or FGFR-3 received IVIG (or blinded placebo) 2 grams/kg followed by 1 gram/kg every 3 wk for a total of 6 treatments. All subjects had Utah Early Neuropathy Scores (UENS), questionnaires and skin biopsies with quantitation of intra-epidermal nerve fiber density (IENFD) taken from adjacent sites at the distal leg at baseline and 6 mo later. The primary outcome was the change in IENFD over 6 mo.

Results: Twenty subjects were enrolled; 17 completed treatment (8 IVIG, 9 placebo). Three did not have final data due to coronavirus disease 2019 (COVID-19). Skin biopsy IENFD improved by 0.5 ± 0.8 fibers/mm in the placebo group and improved by 0.6 ± 0.6 fibers/mm in the IVIG-treated group (p = NS).Over 24 wk the change in pain scores (11 point pain scale) was -1.9 ± 2.6 in the placebo group, and - 1.7 ± 0.9 in the IVIG group (p = NS), the UENS improved by 3.0 ± 5.8 in the placebo group and improved by 1.8 ± 3.9 in the IVIG group (p = NS).

Discussion: This pilot study did not detect a benefit of treatment with IVIG in patients with SFN and autoantibodies to TS-HDS and FGFR-3.