Some studies on the natural history of Graves' orbitopathy: increase in orbital fat is a rather late phenomenon

To describe volumes of orbital fat (FV) and extraocular muscles (MV) in Graves' orbitopathy (GO) as a function of the duration of GO. i) Cross-sectional survey among 95 consecutive patients with untreated GO who had been referred to the combined thyroid-eye clinics of our university hospital. ii) Longitudinal survey among 39 of the 95 patients who did not receive any therapeutic intervention and were followed for 1 year. A computed tomography (CT)-based and well-validated method for calculating orbital soft tissues. In order to neutralize sex differences, results are expressed as ratios of FV:orbital volume (OV) and MV:OV. i) Patients with GO duration of >1 year had greater FV:OV (0.65 vs 0.55, P=0.004), similar MV:OV (0.22 vs 0.21, not significant (NS)), and more proptosis (22 mm vs 21 mm, P=0.03) as compared to those with shorter duration. ii) As compared to baseline, after 1 year, FV:OV had increased (0.56 vs 0.63, P=0.000), MV:OV had not changed (0.19 vs 0.19, NS), proptosis was higher (20 mm vs 21 mm, P=0.003), and clinical activity scores had become lower (2 vs 1, P=0.02) (median values). CT images show that a longer duration of GO is associated with a higher orbital FV. Extraocular MV, however, is not associated with GO duration; rather, it is related to the severity of GO