Successful Treatment of Pretibial Myxedema With Teprotumumab in Thyroid Eye Disease

Background/Objective: Pretibial myxedema (PTM) is a rare extrathyroidal manifestation of Graves’ disease that currently lacks a definitively established standard of care and is without medications presently approved by the Food and Drug Administration for its treatment. Case Report: A 46-year-old woman with Graves’ disease and thyroid eye disease presented with a large, progressive, indurated plaque on her right lower extremity, confirmed by biopsy as PTM. Despite achieving a euthyroid state after total thyroidectomy, the patient's PTM remained refractory to intralesional corticosteroids and topical tofacitinib. After the initiation of teprotumumab, an insulin-like growth factor-1 receptor inhibitor indicated for thyroid eye disease, the patient experienced significant regression of the pretibial plaque's induration, swelling, and discoloration. This clinical response correlated with a marked reduction in thyrotropin receptor autoantibodies, from 259.00 to 24.80 IU/L (reference range ≤1.75 IU/L). Discussion: The natural course of PTM is highly variable. Current treatment options for PTM are limited and often unsatisfactory. Conclusion: This case demonstrates the potential of teprotumumab as a therapeutic option for refractory PTM and supports the hypothesis of a shared pathophysiology involving the thyroid-stimulating hormone and insulin-like growth factor-1 receptors.