Significance of T2 hyperintensity in extraocular muscle hypertrophy

Inflammation of the extraocular muscles (EOM), or myositis, results in an enlargement and thickening of the muscle. This disorder is encountered in orbital inflammation syndrome due to thyroid-associated orbitopathy (TAO) or systemic disease. The goal of this study was to evaluate the significance of T2 hyperintensity on MRI in the case of EOM myositis. In this retrospective study, we focused our data collection on the presence or absence of MRI-T2 hyperintensity in the EOMs and criteria described in the ophthalmologist's record, such as ocular pain, motility restriction, proptosis and redness. MRI examinations were performed on a 3.0T system with a 16-channel head coil, with Gadolinium injection prior to the scan. Conventional structural imaging included axial T1 weighted imaging, axial T2-weighted imaging, and axial, coronal, and oblique sagittal T2-weighted imaging with fat-suppression sequences. In total, 26 patients (42 orbits) were included in this study. Eighteen patients (31 orbits) showed T2 hyperintensity in at least one muscle. Thirty of 31 orbits with T2 hyperintensity showed EOM hypertrophy (P≤0.0001). The mean number of hypertrophied EOMs was 2.67±2.47. Ten patients underwent MRI prior to and after the conclusion of treatment. Interestingly, 50% of all patients with a history of oral corticosteroid treatment for myositis still had T2 hyperintensity on their MRI scans. T2 hyperintensity is strongly correlated with enlargement of the muscle. The persistence of a T2 hypersignal after corticosteroid treatment requires another study to better understand the clinical significance of this parameter.