Differential change in extraocular muscle volume after teprotumumab for thyroid eye disease

To evaluate the effects of teprotumumab on individual extraocular muscle (EOM) volume and proptosis in thyroid eye disease (TED).

A retrospective review was performed using exophthalmometry, clinical activity score (CAS), and orbital imaging before and after teprotumumab treatment. The lateral rectus (LR), medial rectus (MR), superior rectus (SR), inferior rectus (IR) muscles, and the globe were manually segmented individually. Individual and total EOM volumes were calculated and compared between pre- and post-treatment magnetic resonance imaging (MRI).

Mean proptosis reduction after teprotumumab treatment was 3.69 mm (95% CI: 2.82, 4.17, p < 0.001), with an improvement in all orbits. Significant muscle volume reductions occurred in the MR (-20%, p < 0.001) and IR (-28%, p = 0.002) but not the LR (-11%, p = 0.063) or SR (-19%, p = 0.053). Total EOM volume decreased by 20%, while globe volume remained unchanged. CAS and proptosis improved post-treatment, but changes in total EOM volume did not significantly correlate with changes in CAS or proptosis. Pre-treatment IR, MR, and SR volumes showed moderate correlation with total EOM volume reduction.

Teprotumumab significantly reduces EOM volumes, CAS, and proptosis in TED. Weak correlations with clinical outcomes suggest that additional factors, such as orbital fat, influence treatment response.