西川 紗世¹, 西原 永潤², 大下 真紀¹, 山岡 博之², 宮内 昭³, 赤水 尚史²

Sayo NISHIKAWA¹, Eijun NISHIHARA², Maki OSHITA¹, Hiroyuki YAMAOKA², Akira MIYAUCHI³, Takashi AKAMIZU²

¹隈病院臨床検査科, ²隈病院内科, ³隈病院外科

¹Department of Clinical Laboratory, Kuma Hospital, ²Department of Internal Medicine, Kuma Hospital, ³Department of Surgery, Kuma Hospital

キーワード : thyrotoxicosis, Graves’ disease, painless thyroiditis, ultrasonography, vascularity index

【目的】Canon Aplio i800に標準搭載されたVascularity Index（VI）を用い，甲状腺中毒症におけるバセドウ病と無痛性甲状腺炎の鑑別に有用な血流値のカットオフ値を明らかにすることを目的とした．【対象と方法】2023年6月から2025年2月までに当院を初診し，未治療でRI検査および超音波検査にてVIを施行した甲状腺中毒症348例（バセドウ病319例，無痛性甲状腺炎29例）を対象とし，日本甲状腺学会が策定した甲状腺疾患診断ガイドライン2024（2024年改訂）に基づき鑑別診断した．VIを用いて甲状腺血流値（％）を算出し，ROC解析によりカットオフ値を求めた．【結果】バセドウ病と無痛性甲状腺炎の血流値中央値はそれぞれ13％，3.1％であり，バセドウ病で有意に高値であった（p<0.001）．ROC解析により平均血流値のカットオフ値は8.3％（AUC 0.927，特異度100％）であり，約10％が鑑別の目安と考えられた．一方，血流値10％未満のバセドウ病症例も35％存在した．【結論】VIは甲状腺血流を定量的に評価でき10％以上あれば無痛性甲状腺炎は否定できる．一方で，軽症のバセドウ病に関しては血流値のみで判断せず，血液検査や他の検査所見と合わせた総合的評価が重要である．

Purpose: To determine the optimal cutoff value of thyroid blood flow measured using the vascularity index （VI） on a Canon Aplio i800 to differentiate Graves’ disease from painless thyroiditis in patients with thyrotoxicosis. Subjects and Methods: Between June 2023 and February 2025, a total of 348 untreated patients with thyrotoxicosis who first visited our institution and underwent both radioisotope （RI） scintigraphy and ultrasonographic VI assessment were included （Graves’ disease: n=319, painless thyroiditis: n=29）. Differential diagnoses were made in accordance with the Diagnostic Guidelines for Thyroid Diseases 2024 （revised in 2024） established by the Japan Thyroid Association. Thyroid blood flow was quantified as the VI （％）. Receiver operating characteristic （ROC） analysis was performed to determine the optimal cutoff value. Results: The median blood flow values were 13％ for Graves’ disease and 3.1％ for painless thyroiditis, with significantly higher values observed in Graves’ disease （p<0.001）. ROC analysis identified an optimal cutoff value for VI of 8.3％ （AUC=0.927, specificity 100％）. A practical threshold was considered to be approximately 10％. However, 35％ of patients with Graves’ disease showed VI <10％. Conclusion: Quantitative evaluation using the VI is useful for differentiating Graves’ disease from painless thyroiditis, with a cutoff value of approximately 10％ being clinically applicable. However, a comprehensive assessment incorporating laboratory data and other imaging findings is necessary.