Bony Orbital Volume Expansion in Thyroid Eye Disease.

PURPOSE: To quantify changes to the bony orbital volume (BOV) in patients with thyroid eye disease (TED) relative to normal controls.

METHODS: In this case-control study, all patients affected with TED seen over a 2-year period were screened for study entry. Eligible participants were adults with clinical evidence of TED and CT scans of their orbits obtained during the course of their routine care. Exclusion criteria included the history of decompression surgery and/or medical or other ophthalmic conditions that could alter the orbital anatomy. The primary outcome was the measurement of the BOV. Secondary outcome measures included the relationships between BOV and muscle volume, fat volume, Hertel measurements, duration of the disease, and the occurrence of dysthyroid optic neuropathy in patients with TED. Three-dimensional reconstructions of the orbits were created to measure BOV, muscle volume, and fat volume.

RESULTS: A total of 100 participants were included in the study, contributing 200 orbits. This sample was comprised of 50 patients with TED (37 female, 13 male) and 50 controls (37 female and 13 male). There were no differences between the control and patient groups in age or sex. Of the patients with TED, 14 were diagnosed with dysthyroid optic neuropathy (15 orbits, 1 case was bilateral). The mean (standard deviation [SD]) clinical activity score for males was 4.1 (2.29) and 4.35 (2.63) for females. The mean (SD) BOV for males in the TED group was 28.62 ml (3.47), while that of the control group was 24.59 ml (2.19). This difference was significant (p < 0.01). The mean (SD) BOV for females with TED was 24.33 ml (2.39), while that of the female control group was 20.97 ml (1.84). This was again significant (p < 0.01). There was a significant relationship between the BOV and fat volume (p <0.05). There were no significant relationships between BOV and: muscle volume, duration of disease (p = 0.705), Hertel measurements (p = 0.212), age (p = 0.9), and dysthyroid optic neuropathy (p = 0.12).

CONCLUSIONS: This study found that the BOV is significantly greater in patients with TED, suggesting that TED is associated with widespread bony remodeling of the orbit.