Rev Esp Med Nucl Imagen Mol. 2013;32(3):207–208 Interesting image FDG PET/CT findings of thyrotoxicosis induced thymic hyperplasia associated to interferon Hallazgos de la FDG PET/TC en la tirotoxicosis inducida por hiperplasia tímica asociada a interferon G.K. Gedik a,∗ , O. Sarı a , B. Kaya b , E. Varo˘ glu b a Selcuk University, Faculty of Medicine, Department of Nuclear Medicine, Konya, Turkey b Konya Necmettin Erbakan University, Meram Medical Faculty, Department of Nuclear Medicine, Konya, Turkey a r t i c l e i n f o Article history: Received 4 July 2012 Accepted 30 July 2012 Available online 2 October 2012 Interferon-alpha (IFN) is a therapeutic agent which is used for infectious and malignant diseases. Side effects such as flu-like symptoms, hematologic abnormalities and thyroid disease have been reported associated with this therapy. Thyroid disease mani- fests as development of thyrotoxicosis and it may be secondary to destructive thyroiditis or Graves’ disease. Here we report a 61-year-old female patient with malig- nant melanoma. After an IFN treatment duration of 18 months, she started to complain of nervousness, sweating and palpita- tion. Serum free T3, free T4, thyroid stimulating hormone (TSH) and antithyroglobulin antibody (TGAb) levels were 22.27 pg/ml (normal: 2.5–3.9 pg/ml), 5.14 ng/ml (normal: 0.61–1.12 ng/ml), 0.05 IU/mL (normal: 0.34–5.6 IU/mL) and 312.5 IU/mL (nor- mal: 0–115 IU/mL), respectively. Thyroid scintigraphy with 99m Tc pertechnetate was consistent with diffusely increased uptake throughout the thyroid. FDG PET/CT imaging, which was performed for restaging of the melanoma, revealed anterior mediastinal mass in thymus location with elevated FDG uptake (SUVmax 2.91). Thy- rotoxicosis induced thymic hyperplasia must be kept in mind in the differential diagnosis of an anterior mediastinal mass which obviates additional diagnostic work-up. To our knowledge, this is the first report in which FDG PET/CT findings of IFN associ- ated thyrotoxicosis induced thymic hyperplasia have been shown (Figs. 1 and 2). Although disappearance of metabolic activity in subsequent FDG PET/CT evaluations could not be demonstrated, thymic rebound, which was attributed to thyrotoxicosis induced thymic hyperplasia, was thought. Thymic enlargement is a rare phenomenon in adults and is mainly observed after chemotherapy. 1 Thyrotoxicosis may also cause thymic enlargement which is partly due to the stimulatory effect of raised circulating thyroid hormones 2 and partly due to the binding of immunoglobulins to the thymocytes. 3 Formation of thymic medullary lymphoid follicles and thymic hyperplasia is ∗ Corresponding author. E-mail address: goncakara@yahoo.com (G.K. Gedik). Fig. 1. Thyroid scintigraphy revealed enlargement and diffusely increased 99m Tc pertechnetate uptake in both thyroid lobes. found in 38% of patients with Graves’ disease which supports the immunological aspects of thymocyte proliferation. 3 Since the description of the association between IFN and thyroid disease in 1985, 4 high incidence of thyroid abnormali- ties including destructive thyroiditis and Graves’ disease has been reported in patients treated with IFN. 5,6 In our case, presence of TSH receptor antibody or thyroid stimulating immunoglobulin could not be shown but the patient was thyrotoxic and antithy- roglobulin antibodies were present. With the findings of laboratory tests and thyroid scintigraphy, Graves’ disease, instead of destruc- tive thyroiditis, was thought. Thymic rebound and uptake of FDG in thymus have been reported following chemotherapy and also after radioiodine treatment. 7,8 Unusual point of our case was observing FDG uptake 2253-654X/$ – see front matter © 2012 Elsevier España, S.L. and SEMNIM. All rights reserved. http://dx.doi.org/10.1016/j.remn.2012.07.005 2253-8089/$