Euthyroidism and Long-Term Remission of Graves’ Hyperthyroidism Following Treatment With an FcRn Blocker: A Case Report

BACKGROUND: Neonatal fragment crystallizable receptor (FcRn) blockers selectively inhibit FcRn-mediated IgG recycling, resulting in degradation of IgG autoantibodies, including thyrotropin receptor autoantibodies (TSH-R-Ab). METHODS: We describe a case involving a 55-year-old woman with a 17-month history of Graves' disease (GD) who was hyperthyroid despite 15 months on methimazole (MMI) 15-25 mg/day. She received the investigational FcRn blocker batoclimab in a clinical study and was subsequently followed in clinic. RESULTS: Within 1 week of starting weekly subcutaneous batoclimab, serum free triiodothyronine (FT3) and thyroxine (FT4) were normalized. Thyrotropin (TSH) was normal within 4 weeks. MMI was discontinued by study week 6. Twenty-three months after stopping batoclimab, the patient remained off MMI, with normal FT3, FT4, and TSH. Total IgG returned to approximate baseline levels 18 months post discontinuation of batoclimab, whereas TSH-R-Ab, which was elevated at baseline, remained below the upper limit of normal 23 months post batoclimab discontinuation. CONCLUSIONS: FcRn blockade may be an effective and potentially disease-modifying treatment for GD.