Patterns of Extraocular Muscle Enlargement in Graves’ Disease and Acromegaly (P7-10.005)

To determine the patterns of extraocular muscle enlargement in Graves' disease and Acromegaly. Extra-ocular muscle (EOM) enlargement occurs in both acromegaly and Graves' disease, but the degree and pattern of enlargement have not been directly compared in these patient groups. All new patients with a diagnosis of acromegaly or Graves' disease who presented to St Joseph's Healthcare London between January 1, 2015 and July 1, 2020 and who underwent CT scanning with adequate orbital imaging were considered for inclusion. We included age and sex matched control patients with pituitary macroadenomas without thyroid or growth hormone abnormalities. Orbital CT scans were analyzed by a single neuroradiologist, who determined the maximum diameter and cross-sectional area of each EOM. We included 16 patients with Graves' disease, 17 with acromegaly, and 18 controls. Mean maximum diameter of EOMs in Graves', acromegaly, and controls were: inferior rectus (IR)= 5.32±2.19mm, 4.90±0.64mm and 3.76±0.45mm; medial rectus (MR)= 5.38±2.34 mm, 5.03±0.79mm, 3.82±0.35mm; superior rectus (SR)= 5.62±2.29mm, 4.96±0.88mm, 3.71±0.60mm; lateral rectus (LR)= 4.30±1.77mm, 4.73±0.70mm, 3.25±0.44mm. All 4 EOMs were significantly larger in both Graves' (IR, p=0.003; SR, p=0.001; MR, p<0.001; LR, p=0.002) and acromegaly (IR, p=0.034; SR, p=0.023; MR, p=0.032; LR, p<0.001) groups compared to controls, but there was no significant difference between Graves' and acromegaly groups (IR, p=0.629; SR, p=0.471; MR, p=0.391; LR, p=0.541). EOM enlargement extents were similar for each EOM in both Graves' and Acromegaly compared to controls, with the %increase from Graves' to controls as IR: 141%, SR: 141%, MR: 151%, LR: 132%, and Acromegaly IR: 130%, SR: 132%, MR: 134%, LR: 132%. Graves' patients did not show significantly greater EOM hypertrophy compared with acromegaly patients. In both groups, the inferior rectus, medial rectus, and superior rectus did not show different extents of enlargement, contrary to previously described patterns of enlargement(IMSLO) in Graves' disease. Disclosure: Mr. Zajner has nothing to disclose. Mr. Patil has nothing to disclose. Dr. McInnis has nothing to disclose. Dr. Fraser has nothing to disclose. Dr. Bursztyn has nothing to disclose.