Clinical and Radiologic Predictors of Response to Teprotumumab: A 3D Volumetric Analysis of 35 Patients

Purpose: Teprotumumab, a novel human monoclonal antibody, has been shown to reverse the clinical manifestations of thyroid eye disease. Previous reports have suggested that it demonstrates disease-modifying properties through the reduction of orbital fat and muscle volumes. This study aims to analyze orbital volumetric change following treatment and to identify clinical and radiological predictors of response. Methods: This was a prospective longitudinal study with 35 consecutive patients who had available pre- and posttreatment orbital imaging. Three-dimensional volumetric calculations of orbital fat, extraocular muscles, and proptosis were measured using previously validated image processing software. This information was used with demographic data to create a multivariate regression model to review which baseline clinical or radiological factors were predictors of proptosis response. Results: In the study orbit, 20 patients (57%) had a proptosis reduction of ≥2 mm. In the fellow orbit, 18 patients (51%) had a proptosis reduction of ≥2 mm. Regression modeling revealed that baseline proptosis and baseline muscle volumes were significant predictors of proptosis response ( p < 0.01 and p < 0.05, respectively). Further, changes in muscle volume and fat volume were significantly associated with proptosis response ( r = 0.5, p < 0.001 and r = 0.3, p = 0.012, respectively). Conclusion: Teprotumumab significantly reduces orbital fat and muscle volumes. This is manifested by a significant reduction in proptosis. Baseline proptosis and muscle volumes are significant predictors of proptosis response.