Value of Combined Technetium-99m Hydroxy Methylene Diphosphonate and Thallium-201 Imaging in Detecting Bone Metastases from Thyroid Carcinoma

Detectability of bone metastases from differentiated thyroid carcinoma by technetium-99m hydroxymethylene diphosphonate (^99mTc-HMDP) bone scan is considered to be poor. Thallium-201 (²⁰¹T1) is also widely used for detecting metastatic lesions. Our present study was aimed at the evaluation of the combined use of ^99mTc-HMDP and ²⁰¹T1 imaging in successful detection of bone metastases from differentiated thyroid carcinoma. Twenty-seven thyroidectomized thyroid cancer patients (19 females, 8 males; 12 papillary type, 15 follicular type) with 77 bone lesions were included in this retrospective study. All of these patients received ablative doses of radioiodine. Thyroidal origin of the lesions was proved by positive iodine-131 (¹³¹I) uptake. In ¹³¹I-negative lesions, histological proof or absence of tumor markers other than thyroglobulin was considered when computed tomography (CT) and/or magnetic resonance imaging (MRI) suggested metastatic nature of the lesions. Of the 77 lesions, 58 (75.3%) were positive and 19 were negative in the ^99mTc-HMDP bone scintigraphy, whereas 53 lesions (68.9%) could be detected by ²⁰¹T1 scintigraphy. However, within the 19 ^99mTc-HMDP-negative lesions, 14 showed abnormal accumulation of ²⁰¹T1, and within the 24 ²⁰¹T1 negative lesions, 19 were positive in ^99mTc-HMDP scan. This resulted in a combined sensitivity of 93.5%. Our present study concludes that combined ^99mTc-HMDP and ²⁰¹T1 imaging is a sensitive and effective method for detecting bone metastases from thyroid carcinoma.