ABSTRACT
Between January 2000 and December 2001, 60 patients with well differentiated papillary and follicular carcinoma of thyroid gland were followed up. It was found that the destruction or dedifferentiation of thyroid malignant cells caused the failure of the accumulation of I-131 leading to false negative iodine-131 scintigraphy, this was not true with Tl-201 or Tc-99m MIBI. Serum thyroglobulin [Tg] was considered as the gold standard of the presence of residual, recurrence or metastatic lesions in this study. It was found that patients with serum Tg level more than 10 ng/ml had a residual, recurrent or metastatic disease, while patients with serum Tg level<10 ng/ml had no recurrence. Tl-201 WBS, Tc-99m MIBI WBS and serum Tg levels were done in cases with negative I-131 scintigraphy, i.e. 46 patients. All the patients with negative 1-131 scintigraphy were found to be positive by either Tl-201 WBS or Tc-99m MIBI WBS. Tc-99m MIBI or TL-201 scintigraphy has an important role in detection of recurrent or metastatic patients with well-differentiated thyroid carcinoma if I-131 scan is negative and Tg level is elevated as either or both of them were positive in all false negative cases