Antithymocyte Globulin as Second-Line Therapy in Graves Orbitopathy-Preliminary Results From a Prospective Single-Center Study.

Objective: Management of Graves' orbitopathy remains a challenge. Our previous case report has shown promising results for rabbit antithymocyte globulin (rATG) in the treatment of Graves' orbitopathy. Design: We present the response of 7 individuals with active moderate-to-severe steroid-resistant Graves' orbitopathy to rATG, representing preliminary results from a prospective single-center study. Methods: rATG was administered intravenously at a dose of 0.8-1.0 mg/kg daily (cumulative dose of 150-200 mg). The primary outcome measures at weeks 24 and 48 were ≥2-point reduction in Clinical Activity Score from baseline, a proptosis response, a diplopia response, and improvement of distant best-corrected visual acuity and mean retinal sensitivity. Key secondary outcomes included stabilization of ganglion cell complex thickness, a decrease of retinal nerve fiber layer in OCT, and a reduction in CD4/CD8 ratio and TRAb at 48 weeks. Results: An improvement in clinical activity score was observed in all patients, with disease inactivation in 3 cases. Proptosis reduction equal to or greater than 2 mm was noted for 8 of 10 eyes. Diplopia improved in three of 6 patients. There was an improvement in best-corrected visual acuity (from 0.69 to 0.78) and mean retinal sensitivity (from 20.8 to 23.5 dB). In addition, there was a long-lasting improvement in CD4/CD8 ratio in 6 patients. Two patients experienced adverse events (influenza and serum sickness). Conclusion: rATG therapy offers a long-lasting improvement in moderate-to-severe steroid-resistant Graves' orbitopathy with improvement in functional vision (reduction of diplopia, improvement of visual acuity, retinal sensitivity, and VEP pattern). The therapy is well-tolerated. Clinical Trial Registration: ClinicalTrials.gov, identifier NCT05199103.