Extraocular muscle enlargement in thyroid eye disease: a systematic review and meta-analysis.

Objective: While radiographic measurements of orbital structures are used to both diagnose thyroid eye disease (TED) and assess treatment response, the specific extraocular muscle (EOM) changes in TED have not been established. This study aims to systematically review and analyze the difference in EOM sizes in TED patients.

Design: Systematic review.

Methods: The full protocol was registered on PROSPERO (42024566103). The electronic databases EMBASE, Web of Science, and OVID MEDLINE were searched from inception to June 5, 2024, using keywords related to TED and EOMs. Studies were included if they reported EOM measurements in both a TED group and a control group. Data were analyzed using random-effects model meta-analyses, with subgroup analyses based on EOM measurement parameters (i.e., diameter, cross-sectional area, volume).

Results: Twenty-three studies were identified, which together included a total of 2 708 orbits with TED and 1 221 control orbits. Eleven studies were retrospective cohort studies, and 12 were prospective cohort studies. Meta-analysis revealed a mean difference between TED patients and controls in EOM diameter for the inferior rectus of 1.9 mm (95% confidence interval: 1.4-2.3; p < 0.01), medial rectus 1.6 mm (95% CI: 1.1-2.0; p < 0.01), lateral rectus 0.89 mm (95% CI: 0.4-1.4; p < 0.01), and superior rectus 1.3 mm (95% CI: 1.0-1.6; p < 0.01). The mean difference between TED patients and controls in EOM volume for the inferior rectus was 515 mm³ (95% CI: 230-801; p < 0.01), superior rectus was 609 mm³ (95% CI: 327-891; p < 0.01), medial rectus was 551 mm³ (95% CI: 293-810; p < 0.01), and lateral rectus was 288 mm³ (95% CI: 182-393; p < 0.01).

Conclusions: Across studies, there is an apparent enlargement of the inferior rectus in TED compared to controls, but the relative extent of involvement of the medial rectus, superior rectus, and lateral rectus is less consistent.