Differentiated thyroid cancer: Case report of false positive I 131 uptake on whole body scintigraphy in a patient with bilateral femur osteonecrosis

Objective: Differentiated thyroid cancer (DTC) is one of the fastest growing cancers worldwide. Despite the generally good prognosis of thyroid carcinoma, about 5% of patients will develop metastatic disease, exhi-biting a more aggressive behavior. Radioiodine whole-body scintigraphy (WBS) has been used in the detec-tion of DTC. Radioiodine is a sensitive marker for detection of thyroid cancer; however, radioiodine uptake is not specific for thyroid tissue. It can also be seen in healthy tissue as well as in inflammation, or in a variety of benign and malignant non-thyroidal entities. Subject and Methods:The subject of the present case report is a 52 years old man with brain metastatic DTC who received radioiodine therapy and corticosteroids as pal-liative therapy. Whole-body scintigraphy revealed bilateral iodine uptake of the femur. Corticosteroid thera-py is among the most widely recognized risk factor for osteonecrosis, which at the present case had to be re-cognized as a false positive (iodine-131) I uptake in order to avoid diagnostic error. Results: Post thera-131 peuticwhole body scintigraphy revealed no uptake in the thyroid bed as well as pathologic uptake of radio -iodine in both femurs. The magnetic resonance imaging (MRI) of the femurs combined with the history of long term exposition on high doses of corticosteroids evidenced diagnosis of steroid-induced osteonec-rosis of the femurs. Conclusion: Radioiodine WBS plays an important role in clinical decision making for the evaluation and the management of patients with DTC. Despite its high range of sensitivity and specificity, a variety of reports of false positive whole body scans has demonstrated a diversity of causes. Comprehension of the physiology of iodine uptake and of the pathophysiology of clinical entities which end up giving false positives scans, provides clinicians a useful tool in order to avoid diagnostic and therapeutic errors as far as DTC is concerned.