Early Radiologic Response to Teprotumumab in Acute Dysthyroid Optic Neuropathy with Insufficient Response to Steroid Pulse Therapy: A Longitudinal Quantitative MRI Analysis

Teprotumumab is an insulin-like growth factor-1 receptor inhibitor that has recently emerged as a potential treatment for dysthyroid optic neuropathy (DON). However, sequential orbital magnetic resonance imaging (MRI) changes after steroid pulse therapy and subsequent teprotumumab treatment remain insufficiently characterized. Herein, we report a case of acute DON associated with active thyroid eye disease that did not show clear early improvement after high-dose intravenous methylprednisolone wherein teprotumumab was then initiated, followed by rapid improvement in visual function. MRI after steroid pulse therapy showed no consistent reduction in extraocular muscle size, whereas MRI performed 11 days after the first teprotumumab infusion demonstrated an early reduction, particularly near the orbital apex, with improvement in apical crowding. This reduction progressed after the fourth infusion and remained evident through completion of the eighth infusion. The enlarged lacrimal glands also showed an early bilateral reduction, supporting an anti-inflammatory effect during the early phase of treatment. These MRI findings suggest that teprotumumab rapidly reduces orbital tissue enlargement and relieves optic nerve compression in patients with acute DON. Early and sustained extraocular muscle reduction may represent a clinical advantage over steroid pulse therapy, and support further evaluation of teprotumumab as an early treatment option for DON.