Effects of various extraocular muscle enlargement patterns on muscle diameter index in graves ophthalmopathy patients: a retrospective cohort study

Graves ophthalmopathy (GO) patients often undergo retrobulbar injection of glucocorticoids (GCs) as a common therapeutic approach. This study aimed to explore the impact of various patterns of extraocular muscle (EOM) enlargement on EOM changes following retrobulbar GCs injection in patients with GO. A retrospective analysis was conducted on GO patients who underwent retrobulbar GCs injections. Data pertaining to EOM diameter (EMD) and muscle diameter index (MDI) were collected from orbital computed tomography (CT) scans. The MDI change (ΔMDI) was calculated by comparing pre- and post-injection MDI values. The relationship between each pre EMD/MDI and ΔMDI was assessed using univariate and multivariate logistic regression analysis. A total of 68 patients with GO were included in this study, accounting for 118 eyes. After retrobulbar injections of GCs, 84 eyes showed a decrease in the MDI, while 34 eyes exhibited an increase in MDI. A threshold effect was observed in the relationship between medial pre EMD/MDI and ΔMDI. When the medial pre EMD/MDI was less than 0.28, a higher medial pre EMD/MDI was associated with a smaller ΔMDI (β = − 25.21, p = 0.0175). However, when the medial pre EMD/MDI was greater than 0.28, no significant association was found between pre EMD/MDI and ΔMDI. There was a negative correlation between medial + lateral pre EMD/MDI and ΔMDI (β = − 11.76, p < 0.0189). A higher medial + lateral pre EMD/MDI was associated with a greater decrease in MDI. Additionally, there was a positive correlation between superior rectus muscle-levator complex (SRLC) pre EMD/MDI and ΔMDI (β = 11.92, p = 0.040). The higher the value of SRLC pre EMD/MDI, the greater the ΔMDI. There was an association between pre EMD/MDI and changes in EOMs after retrobulbar injection of GCs in GO patients. In patients with predominantly enlarged medial rectus muscles and severe degrees of enlargement, retrobulbar injection of GCs should be assessed for its benefit; a combination of medial and lateral rectus muscle enlargement is beneficial for the shrinkage of EOMs following retrobulbar injections; the involvement of the SRLC rectus muscle may be a disadvantageous pattern of shrinkage of EOMs following retrobulbar injections.