Increased extraocular muscle volume tied to dysthyroid optic neuropathy in patients with thyroid eye disease

Increase in extraocular muscle volume tied to dysthyroid optic neuropathy in patients with thyroid eye disease suggests a new study published in the Canadian Journal of Ophthalmology. A study investigated extraocular muscle volumes in thyroid eye disease (TED) patients with and without dysthyroid optic neuropathy (DON). The extraocular muscles were manually segmented into consecutive axial and coronal slices, and the volume was calculated by summing the areas in each slice and multiplying by the slice thickness. Data were collected on patient demographics, disease presentation, thyroid function tests, and antibody levels. Results: Imaging from 200 orbits was evaluated. The medial rectus, lateral rectus, superior muscle group, inferior rectus, and superior oblique volumes were significantly greater in orbits with dysthyroid optic neuropathy than TED orbits without dysthyroid optic neuropathy (p < 0.01 for all). There was no significant difference in the inferior oblique muscle volume (p = 0.19). An increase in the volume of the superior oblique muscle showed the highest odds for dysthyroid optic neuropathy. Each 100 m3 increase in superior oblique, lateral rectus, inferior rectus, medial rectus, and superior muscle group volume was associated with 1.58, 1.25, 1.20, 1.16, and 1.14 times increased odds of dysthyroid optic neuropathy. All extraocular muscle volumes except for the inferior oblique were significantly greater in dysthyroid optic neuropathy patients. Superior oblique enlargement was associated with the highest odds of dysthyroid optic neuropathy, suggesting superior oblique enlargement to be a novel marker of dysthyroid optic neuropathy.