Effect of (131)iodine therapy on the course of Graves' ophthalmopathy: A quantitative analysis of extraocular muscle volumes using orbital magnetic resonance imaging

There remains uncertainty as to the effect of radioactive iodine (I-131) th erapy on the associated ophthalmopathy (GO). Twenty newly diagnosed patient s with Graves' hyperthyroidism treated with I-131 (median dose, 15.5 mCi) w ere followed with ophthalmologic evaluations (OE) and magnetic resonance im aging (MRI) at baseline, 2, and 6 months, and with OE alone at 3 years. For MRI, the superior, inferior, and medial rectus muscle volumes and total mu scle volumes (TMV) were measured. Replacement levothyroxine was initiated a s low thyroxine (T-4) levels were noted. At baseline, 10 patients (50%) sho wed evidence of mild GO by OE and/or MRI. There was a significant differenc e in TMV between the 20 patients with Graves' hyperthyroidism and 10 contro ls (mean +/- standard error [SE]; 2,652 +/- 118 vs. 2,046 +/- 96 mm(3); P = 0.002) and between the 10 patients with and 10 without GO (3,006 +/- 96 vs . 2,298 +/- 61 mm(3); P = 0.001). TMV correlated with the Hertel score (r = 0.56, P = 0.01). TMV showed no significant change at 2 or 6 months posttre atment. The inferior rectus volume increased slightly at 2 months posttreat ment (P = 0.03) but remained stable at 6 months. Furthermore, no significan t changes occurred in Hertel scores or in clinical assessments up to 3 year s posttreatment and none showed worsening or new development of GO. In conc lusion, our results show no significant risk for radioiodine-induced initia tion or progression of mild GO.