Incidental thyroid uptake during 99mTc-methylene diphosphonate bone scintigraphy in oncologic patients

Introduction: Extraosseous accumulation of 99mTc – methylene diphosphonate (MDP) may be due to neoplastic, dystrophic, hormonal, inflammatory, ischemic, traumatic or excretory disorders. 99mTc-MDP incidental thyroid uptake is not frequent and is possibly caused by the presence of dystrophic or metastatic calcification, biopsy procedure and presence of benign or malignant thyroid nodules. To analyze the etiological factors leading to 99mTc-MDP uptake in the thyroid gland. Methods: Fifty patients (pts), 19 females (38%) and 31 males (62%), 62±12 years, with no pervious history of thyroid disease, were included in the study. In the period January 2016 – January 2018, all pts underwent MDP bone scintigraphy due to oncologic indication and incidental tracer uptake was noted in the region of the thyroid gland. Ultrasonography (US) was performed in all pts. Patients with detected nodules underwent 99mTc-pertechnetate scintigraphy and fine needle aspiration cytology (FNAC). Thyroid hormone and autoantibodies levels were also analyzed. SPECT/CT procedure was performed in all patients to precisely localize the MDP uptake. Results: Thirty-nine patients had calcifications in the thyroid gland (29 with microcalcifications and 10 with macrocalcifications). In 23 patients, thyroid nodules were detected. 99mTc-pertechnetate scintigraphy presented 15 cold nodules and 8 nodules with increased tracer uptake. FNAC in 3 patients presented nuclear anisocariosis, with Hurthle cell metaplasia, and surgery was advised. In 11 patients, thyroid cartilage calcifications were detected. Conclusion: Incidental findings of thyroid 99mTc-MDP accumulation during bone scintigraphy indicate presence of additional, previously unexpected, active disease processes.