99mTc-MIBI and 131I scintigraphy in the follow-up of differentiated thyroid carcinoma (DTC) patients after surgery

Full text: MIBI scan has been reported to be a highly sensitive imaging technique for detection of differentiated thyroid carcinoma (DTC) metastases that have lost the capability to uptake 131I. The purpose of the present study was to evaluate retrospectively the value of the 99mTc-MIBI scan and 131I whole body scintigraphy using thyroglobulin (Tg) levels as a basis to comparison. Eighty-four patients (63F/21M) with an age of 17-74 yr (mean 43.5 yr) with DTC (47 cases with papillary, 18 cases with follicular and 19 cases with papillary-follicular ) were assessed. All of them had undergone total or near-total thyroidectomy and received radioiodine treatment for ablation of post surgical residual thyroid tissue. They were examined after L-thyroxin withdrawal oven 4-5 weeks in the follow-up of DTC. Planar and whole body images were acquired at 15 min and 180 min after i.v. application of 99mTc-MIBI (555-740 MBq) and at 48 h after p.o. administration of 131I (111-185 MBq) on Toshiba GCA gamma camera. Serum Tg assays were performed to clarify the presence of residual recurrent malignancy. All scintigraphic findings were compared to US, CT or MRT data. 131I scan was positive in 55 patients showing thyroid remnants in 31 cases, lymph node metastases in 24 cases (17 in the neck, 7 to neck/mediastinum), pulmonary metastases - in 6 cases and bone lesions - in 2 cases. In 18 patients 131I scan was negative, Tg was undetectable, so patients considered tumour-free. In 11 patients 131I scan was negative while serum Tg was increased. These false negative results were observed predominantly in cases with less differentiated metastatic cells, especially after several courses of high-dose 131I therapy. 99mTc-MIBI scan revealed the presence of lymph node and/or lung metastases (non-functioning metastases) in 9 of them, false negative results were obtained in 2 cases. Serum Tg was increased in all patients with local lymph node and distant metastases, visualized by 131I or by 99mTc-MIBI, but also in 18 patients with thyroid remnants only. Considering 131I scan as the most specific standard procedure we may conclude that the combined 99mTc-MIBI scintigraphy and serum Tg assay appear to be an alternative substitute of radioiodine diagnostic imaging to demonstrate the extent of the disease in cases with DTC and elevated Tg. (author)