IVIg for Small Fiber Neuropathy With Autoantibodies TS-HDS and FGFR3
Small fiber neuropathies, and mixed small and large fiber neuropathies, have many potential causes including diabetes, vitamin deficiencies, environmental and toxic exposures, HIV, autoimmune and paraproteinemias.
However, despite this broad differential at least 30% of cases of small fiber neuropathies remain idiopathic. There is therefore a growing interest in the potential for using IVIG in small fiber neuropathy without direct proof that the disorder is caused by immune reactions. We have recently uncovered two novel autoantibodies, TS-HDS and FGFR-3, that are targeted again peripheral neural structure. TS-HDS is a disaccharide component of glycosylation of heparin and heparin sulfate.
Patients with elevated levels of IgM against TS-HDS display clear small fiber loss with IgM deposits around the outside of medium- & larger-sized capillaries with C5b-9 complement deposits. FGFR-3 is a secreted cell surface receptor; genetic defects of FGFR-3 are linked to achrondroplasia and other bony abnormalities.
The antibodies to TS-HDS and FGFR-3 are detected in up to 20% of patients with otherwise idiopathic small fiber neuropathy, but are rare in patients without small fiber neuropathy.
Dr. Levine (a co-investigator on this project) recently presented 3 cases of small fiber associated with elevated levels of auto-antibodies to TS-HDS or FGFR-3 who were treated with IVIG at 2 gm/kg/month for 6 months. He examined skin biopsies for intra-epidermal nerve fiber density and patient self-reported pain scores at baseline and after six months of therapy. All 3 cases showed marked improvement in pain scores. The average reduction in pain was 54%. In addition there was a clear increase in the intra-epidermal nerve fiber density (IENFD) after 6 months of therapy. Pre-treatment IENFD was 1.6, 1.7, and 2.4 at the calf. After 6 months of therapy the IENFD was 8.4, 5.7, 3.3 respectively (these are clinically significant improvement in nerve fiber density.
The investigators believe these anecdotal cases suggest that TS-HDS and FGFR-3 antibodies may be a marker for a group of SFN patients that are immune mediated and may respond to IVIG. (This case series was presented as a poster at the American Academy of Neurology meeting in 2017)