症例1は70代女性で、甲状腺乳頭癌の術後肺転移に対し放射性ヨウ素内用療法が施行されたが病変の増大が認められたため、放射性ヨード不応性甲状腺癌を疑い、FDG-PET/CTイメージングを施行した。症例2は60代男性で、甲状腺癌の術後に未分化癌と病理診断され肺転移も伴っていた。放射性ヨウ素内用療法が予定されFDG-PET/CTイメージングが施行され、FDGの異常集積が描出されたため放射性ヨード不応性甲状腺癌が疑われた。両例ともにFDG-PET/CTイメージングでは肺転移巣に強いFDG異常集積が描出され、放射性ヨード不応性が示唆されたため、高周波アブレーションによる治療が選択された。なお、治療後のCT検査では転移巣の退縮が観察され再発もみられなかったため、放射性ヨード不応性甲状腺癌に通常用いられるチロシンキナーゼ阻害薬(TKI)の投与は施行しなかった。本例から、甲状腺癌の肺転移に対する治療戦略の決定に、TKI開始前のFDG-PET/CT撮像による視覚的再病期分類の重要性が指摘された。

Fluorodeoxyglucose-positron emission tomography/computed tomography (FDG-PET/CT) is valuable for visually staging recurrent thyroid cancer, particularly in patients with suspected radioactive iodine-refractory pulmonary metastasis from thyroid cancer. In Case 1, despite undergoing radioactive iodine therapy for pulmonary metastasis following papillary thyroid carcinoma surgery, an increase in the metastatic lesion was observed, prompting the suspicion of iodine refractivity. FDG-PET/CT imaging revealed strong abnormal FDG accumulation in the pulmonary metastases. In Case 2, a pulmonary metastasis from thyroid cancer was originally pathologically diagnosed as a poorly differentiated tumor, and FDG-PET/CT imaging was conducted due to suspected iodine refractivity. Both patients showed a single pulmonary metastasis site that was considered iodine-refractory. Radiofrequency ablation (RFA) for pulmonary metastases of thyroid cancer may delay the introduction of tyrosine kinase inhibitors (TKIs), which are commonly used for iodine-refractory thyroid cancer; however, their use is associated with side effects and high medical costs. RFA was performed in cases 1 and 2, and both patients progressed without recurrence; thus, TKIs were not administered. Visual staging using FDG-PET/CT before TKI initiation for pulmonary metastases from thyroid cancer is beneficial in determining treatment strategies.

DOI： 10.32291/nmj.6.0_1

A man in his 70s who had undergone total thyroidectomy for thyroid cancer was admitted to our department for I-131 radioiodine remnant thyroid ablation and was administered 3.33 GBq of I-131, and a confirmatory scintigraphy was performed 10 days after administration. MIP images showed abnormal I-131 distribution scattered throughout the body, in addition to abnormal I-131 accumulation in the thyroid bed. SPECT/CT images showed that the abnormal distribution of I-131 was within the skin and muscles, and there were many small objects of high density corresponding to the abnormal accumulation. These objects were approximately 1 to 5 mm in size on the CT images. According to the patient, when he was in his 20s, he underwent needle-burying acupuncture to treat stiff shoulders and lower back pain, in which a 24-karat gold needle was inserted into the affected area, cut, and buried.

DOI： 10.32291/nmj.6.0_7