Purpose: To objectively measure the differential expansion of orbital fat and muscle volume in patients with thyroid eye disease.
Methods: In this retrospective study, eligible participants were adults with clinical evidence of thyroid eye disease and high-resolution computed tomography scans of their orbits. Patients with a history of decompression surgery and/or medical or other conditions that could alter the orbital anatomy were excluded. Three dimensional reconstructions of the orbits allowed the calculation of the fat volume, muscle volume and bony orbital volume using the MIMICS imaging analysis tool. Both orbits from each patient were included without bias through the use of the generalized estimating equation. The primary outcome was the measurement of fat volume. Secondary outcome measures included the correlation of the muscle volume, bony orbital volume and exophthalmometry with age.
Results: Fifty patients with thyroid eye disease who were included contributed 100 orbits. The sample included 29 females (age 57, standard deviation = 14.8) and 21 males (age 52, standard deviation = 18.14). Mean (standard deviation) exophthalmometry measurement was 21.58 (4.01). Fat volume and exophthalmometry were negatively correlated with age (p = 0.00001 and p = 0.00001, respectively). Muscle volume (p = 0.985) and bony orbital volume (p = 0.484) did not correlate with age.
Conclusion: Older patients with thyroid eye disease have less expansion of fat volume compared with younger patients. There are no associations between age and the bony orbital volume or muscle volume. These results support the growing body of evidence which suggests that the pathophysiology of TED is different in older patient.
Keywords: Thyroid; graves; orbitopathy.