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PurposeThyroid eye disease (TED) is a progressive, debilitating and potentially vision-threatening autoimmune disease. Teprotumumab, a novel human monoclonal antibody, has been shown to reverse the clinical manifestations of TED. Patients receiving teprotumumab have been shown in two multicenter, randomized placebo-controlled trials to have decreased proptosis, diplopia and inflammation after 24 weeks of treatment. This study aims to analyse volumetric and inflammatory changes on orbital imaging prior to and after teprotumumab treatment from one of these trials.DesignRetrospective review.SubjectsSix patients enrolled in the phase III teprotumumab clinical trial (OPTIC, NCT03298867) with active TED who received 24 weeks of teprotumumab and had pre- and post-treatment orbital imaging (CT or MRI). Additionally, 12 non-TED patients (24 orbits) were analysed as a comparative control group.Methods3D volumetric calculations of the extraocular muscles (EOMs), orbital fat, and bony orbit were measured using previously validated image processing software. 3D volumetric results and changes in EOM inflammation were compared with clinical measurements of TED.ResultsTotal EOM volume within each orbit was markedly reduced post-teprotumumab in all patients (n=six patients, 12/12 orbits, p<0.02). There was no statistical difference in post-treatment EOM volume when compared to non-TED controls. Total orbital fat volume was also reduced in 11 of 12 studied orbits (n=six patients, p=0.04). Overall EOM inflammation based on MRI signal intensity ratio was reduced in 8/8 orbits (n=four patients, p<0.01).ConclusionOrbital imaging demonstrated decreased EOM volumes and orbital fat tissue volumes after teprotumumab treatment.