Technetium-99m-MIBI in the follow-up of differentiated thyroid carcinoma

Abstract

Technetium^-99m-methoxyisobutil isonitrila (^99mTc-MIBI) has been introduced as a tumor-seeking agent in the past few years. The present study has evaluated the role of ^99mTc-MIBI whole body scan (WBS) in localizing metastatic lesions by assessing sensitivity and specificity in comparison with ¹³¹I scan and serum thyroglobulin measurement. Eighty-nine thyroidectomized patients due to differentiated thyroid cancer were enrolled. Early (20 minutes) and delayed (6 and 24 hours) whole body images were obtained after ^99mTc-MIBI injection. Tg measurements were obtained during thyroid hormone reposition and 4 weeks after hormone discontinuation, ¹³¹I scans were performed after low diagnostic or high ablative/therapeutic dose. These methods were used as standard to evaluate the presence of residual or metastatic thyroid cancer. The patients with ^99mTc-MIBI scan positive and ¹³¹I negative scan underwent chest x-ray, computed tomography (CT) or magnetic resonance imaging (MRI). In the group with ¹³¹I negative scan (34/89), 23 patients presented ^99mTc-MIBI WBS negative and 11 patients were discordant (specificity: 67,6%), and 22 patients had ^99mTc-MIBI WBS and ¹³¹I scan positive; while the total of ¹³¹I scans positive was 55 (sensitivity: 40,0%). Eleven patients had ¹³¹I scan negative and ^99mTc-MIBI WBS positive; seven of those proved to be true positive. Although ^99mTc-MIBI has low sensitivity on detection of tumor recurrence, it may have a role as a supplementary tool to thyroglobulin measurements and ¹³¹I scans.