Reliability of extraocular muscle biomechanics in the evaluation of disease activity in thyroid eye disease.

To evaluate extraocular muscle (EOM) stiffness in the identification of different stages of thyroid eye disease (TED) and to explore its associations with magnetic resonance imaging parameters. This retrospective cross-sectional study included 58 participants (19 with active TED, 21 with inactive TED, and 18 controls) and used real-time elastography and magnetic resonance imaging to determine the elastic ratio, native T1 value, and extracellular volume (ECV) fraction of EOMs. Correlation analysis of these parameters was performed, and receiver operating characteristic curves (ROC) were generated to assess their ability to evaluate TED clinical activity. Compared with controls, the elastic ratio of the medial rectus (MR) muscles was significantly higher in patients with inactive TED and significantly lower in those with active TED (P < 0.05). The elastic ratio and mean ECV fraction were strongly correlated in the MR muscles (r = 0.91) and moderately correlated in the lateral rectus muscles (r = 0.72). The are a under the ROC (AUROC) for the elastic ratio (AUROC = 0.919) was higher than that for the mean ECV fraction (AUROC = 0.847) in the MR muscles; however, both showed a comparable ability to diagnose inactive TED (P = 0.13). The optimal cutoff value of the elastic ratio in MR muscles was 6.4, which detected inactive TED with a specificity of 76.2% and sensitivity of 89.5%. The EOM elastic ratio increased with the progression of TED from the active to the inactive phase, and is a useful clinical marker of EOM fibrosis. Our study provides novel evidence for the easier and noninvasive clinical assessment of TED activity via the detection of EOM fibrosis using biomechanics.