Age-related difference in extraocular muscles and its relation to clinical manifestations in an ethnically homogenous group of patients with Graves' orbitopathy

Abstract

Purpose: To evaluate the age-related difference in EOMs and its relation to clinical manifestations by computed tomography (CT) measurement of EOMs.

Methods: The medical records and CT image review of 40 patients (80 orbits) with moderate-to-severe Graves' orbitopathy were performed. The patients were divided into two age groups, group 1 (≤ 40 years) and group 2 (> 40 years). CT scans of 30 gender- and age-matched normal controls were also obtained. The maximal cross-sectional area (MCA) and its position (pMCA) of each EOM were measured.

Results: Group 1 presented with more severe proptosis (p < 0.001), while group 2 had a higher risk of diplopia (p < 0.001). Motility restriction in supraduction was more likely to occur in Group 2 (p = 0.027) with even higher severity (p = 0.047). The pMCA was higher in the inferior (p = 0.001), medial (p = 0.021), and lateral rectus (p = 0.013) in group 1. Proptosis was positively correlated to pMCA while diplopia was correlated to MCA in both groups. Significant correlation was noted between restrictions levels and MCA (superior, r = 0.467, p < 0.001; inferior, r = 0.358, p = 0.007; medial, r = 0.314, p = 0.018; lateral, r = 0.308, p = 0.021) or pMCA (inferior, r = - 0.534, p < 0.001) only in group 2.

Conclusions: The muscle enlargement patterns are significantly different between younger and older patients. Older patients tended to have enlarged muscle bellies more posterior in the orbit, which is responsible for more diplopia and motility restriction. Proptosis is more likely to be affected by the most enlarged position than muscle size. So younger patients tended to develop more proptosis and be less bothered by motility restriction even with enlarged muscles.

Keywords: Computed tomography; Extraocular muscles; Graves’ orbitopathy; Quantitative analysis; Thyroid eye disease.