Orbital flourine-18-fluorodeoxyglucose positron emission tomography in patients with Graves’ disease for evaluation of active inflammation Lebriz Uslu-Beşli a , Levent Kabasakal a , Sait Sağer a , Erdoğan Cicik b , Sertaç Asa a and Kerim Sönmezoğlu a Objective Prediction and early diagnosis of orbitopathy is needed in patients with Graves’ disease, especially when radioiodine therapy is planned. Positron emission tomography/computerized tomography (PET/CT) using flourine-18-fluorodeoxyglucose (FDG) is an effective imaging modality in detection of inflammation, however, its ability to detect orbital inflammation has not been well studied. The aim of our study is to determine the ability of FDG PET/CT to detect orbital inflammation related with Graves’ disease, identify active orbitopathy, predict the radioiodine-triggered orbitopathy, and find out the effects of radioiodine on orbital inflammation. Materials and methods Total 31 Graves’ disease patients and 17 controls were included. All Graves’ disease patients underwent cranial FDG PET/CT imaging prior therapy. Radioiodine therapy and post-treatment PET/CT study was applied to 21 patients. PET/CT images of all examinees were evaluated, measuring extraocular muscle maximum standard uptake value (SUV max ) and muscle thickness. Results FDG uptake was increased in the majority of extraocular muscles in Graves’ disease patients in comparison to controls and this increase was found to be irrelevant from muscle thickness. Extraocular muscle SUV max values did not increase in Graves’ orbitopathy patients who received radioiodine under corticosteroid prophylaxis. SUV max level of all orbital rectus muscles were increased after radioiodine therapy in nonsmokers, whereas no increase was detected in smokers. Conclusion FDG PET/CT may be helpful in detection of extraocular muscle inflammation and it may show ongoing orbitopathy in early stages of inflammation before anatomical changes occur. Nucl Med Commun 38:964–970 Copyright © 2017 Wolters Kluwer Health, Inc. All rights reserved. Nuclear Medicine Communications 2017, 38:964–970 Keywords: fluorodeoxyglucose, Graves’ disease, Graves’ orbitopathy, positron emission tomography, radioiodine Departments of a Nuclear Medicine and b Ophthalmology, Cerrahpaşa Medical Faculty, Istanbul University, Fatih/Istanbul, Turkey Correspondence to Lebriz Uslu-Beşli, MD, Department of Nuclear Medicine, Cerrahpaşa Medical Faculty, Istanbul University, Fatih/Istanbul 34098, Turkey Tel: + 90 212 414 3000; fax: + 90 212 632 0050; e-mail: lebriz@gmail.com Received 2 March 2017 Revised 24 April 2017 Accepted 9 August 2017 Introduction Graves’ disease is an autoimmune disease, caused by autoantibodies against thyroid antigens and the disease is characterized by a classical triad of hyperthyroidism, exophthalmos, and pretibial myxedema [1,2]. Although Graves’ orbitopathy is relatively rare in population, orbi- topathy can be seen in about half of patients with Graves’ disease and it has a severe course in 3–5% of the cases [3]. Several immune system elements play role in the development of orbitopathy. The major antigen causing T and B-lymphocyte-based immune reaction is thyroid- stimulating hormone (TSH) receptor [4]. Genetic and environmental factors are also present in the pathogen- esis of the disease. Graves’ disease is more common in females (female/male ratio: 6–8/1) and it is generally seen between 30 and 50 years of age. Moreover, several bacteria-related superantigens, smoking and radioactive iodine are the other factors entitled with the develop- ment and progression of the Graves’ disease or the rela- ted orbitopathy [4]. Although the onset of exophthalmos is generally con- comittant with the onset of hyperthyroidism, they can also start seperately and the severity of orbitopathy can vary among patients [5]. Orbitopathy may become inac- tive in the course of the disease and the detection of the presence of active orbitopathy is needed in therapy planning of these patients. Although several effective treatment modalities are present for the treatment of hyperthyroidism, such as radioiodine therapy or surgical resection and antithyroid drugs, treatment of the orbito- pathy is difficult, and surgery is only applied to selected patients with advanced eye disease. Therefore the real challenge in treatment of Graves’ disease is not the treatment of hyperthyroidism, rather it is the treatment of hyperthyroidism without aggravating orbitopathy [6,7]. Radioactive iodine is commonly used as an effective method in treatment of hyperthyroidism. However, radioactive iodine itself may also aggravate the orbito- pathy [8]. Glucocorticoids are therefore recommended to be used with radioiodine to reduce the radioiodine Original article 0143-3636 Copyright © 2017 Wolters Kluwer Health, Inc. All rights reserved. DOI: 10.1097/MNM.0000000000000737 Copyright r 2017 Wolters Kluwer Health, Inc. All rights reserved.