Extended Long-Term Follow-Up of Proptosis Regression After Teprotumumab Treatment for Thyroid Eye Disease

PURPOSE: A previous study found high rates of proptosis regression after teprotumumab treatment for thyroid eye disease, though having been published relatively early in the teprotumumab era, it had gaps in follow-up frequency and duration. This study extends on the previously reported cohort to better understand teprotumumab's durability. METHODS: Retrospective analysis of all patients who completed all 8 teprotumumab infusions at 1 institution from January 1, 2020 to December 31, 2022. Primary outcomes were proptosis regression at most recent follow-up compared with immediately posttreatment and pretreatment. RESULTS: Of 113 patients, 150 (66.4%) eyes of 83 patients had regression at most recent follow-up (mean 20.4 months posttreatment) compared with immediately posttreatment, averaging 2.8 mm (range 0.5-10.0). Ninety-five eyes of 55 patients (42.0%) regressed by ≥2 mm (mean 3.8, range 2.0-10.0). Mean time to first documentation of regression was 10.2 months (range 2.7-39.0); 67.2% of eyes continued to worsen after initial regression. Compared with pretreatment, 137 eyes of 77 patients (60.6%) had net improvement, averaging 2.7 mm (range 0.5-10.0), while 71 eyes of 43 patients (31.4%) regressed to become worse than pretreatment by 1.8 mm (range 0.5-5.0). Thyroid eye disease flare occurred in 61 (54.0%) patients, defined as a clinical activity score increase ≥2 (n = 6, 5.3%), proptosis regression ≥2 mm (n = 37, 32.7%), or both (n = 18, 15.9%). CONCLUSIONS: This extended follow-up analysis demonstrated proptosis regression after teprotumumab in two-thirds of eyes at long-term follow-up, with one-third worsening beyond pretreatment proptosis. Two-thirds continued to worsen after initial regression, and over half of patients developed a thyroid eye disease flare. Though most patients maintained net improvement, these results suggest that proptosis effects are not durable in most patients after standard teprotumumab dosing.