USEFULNESS OF TC-99M HYDROXYMETHYLENE DIPHOSPHONATE SCANS IN LOCALIZING BONE METASTASES OF DIFFERENTIATED THYROID-CARCINOMA

Iodine-131 is uniquely able to demonstrate iodine uptake of differenti ated thyroid carcinoma (DTC), but precise localization may be difficul t, especially in the thorax, due to the quality of image resolution wi th I-131 and the lack of anatomical landmarks. When bone metastases do not show radioiodine uptake, bone scintigraphy can be used to detect them. We studied two groups of patients. In group 1, 15 patients with known bone metastases of DTC were treated with 3.7 GBq I-131. After 4 or 5 days, technetium-99m hydroxymethylene diphosphonate (HMDP; 740 MB q) was injected and a whole-body scan with simultaneous acquisition of I-131 and Tc-99m-HMDP images was carried out using a large field of v iew gamma camera fitted with a high-energy collimator. Technetium upta ke was abnormal in 47 of 63 localizations, being increased in 29 foci, decreased in 7 and heterogeneous in 11. The superimposition of I-131 and Tc-99m-HmDP scans permitted an accurate localization in 80% of spi ne metastases and in 46% of osseous thoracic localizations, even in th e presence of lung metastases. In group 2, 9 patients, who had bone pa in, neurological signs or elevated serum thyroglobulin, had DTC bone m etastases without iodine uptake. They received a diagnostic dose of Tc -99m-HMDP 3h prior to scintigraphy with a large field of view gamma ca mera fitted with a low-energy collimator. Technetium uptake was abnorm al in 37 of 38 localizations, being increased in 34 foci and decreased in 3. One false-negative was found in a skull metastasis. In both gro ups of patients, Tc-99m-HMDP scans were useful. The procedure allows a ccurate localization of bone metastases and can be used as a guide for subsequent radiological investigations.