The usefulness of 99mTc-sestaMIBI thyroid scan in the differential diagnosis and management of amiodarone-induced thyrotoxicosis

Background: Amiodarone-induced thyrotoxicosis (AIT) is caused by excessive hormone synthesis and release (AIT I) or a destructive process (AIT II). This differentiation has important therapeutic implications. Purpose: To evaluate 99mTc-sestaMIBI (MIBI) thyroid scintigraphy in addition to other diagnostic tools in the diagnosis and management of AIT. Subjects and methods: Thyroid 99mTcOK4 and 99mTc-MIBI scintigraphies were performed in 20 consecutive AIT patients, along with a series of biochemical and instrumental investigations (measurement of thyrotrophin, free thyroid hormones and thyroid autoantibodies; thyroid colour-flow Doppler sonography (CFDS) and thyroid radioiodine uptake (RAIU). Results: On the basis of instrumental and laboratory data (excluding thyroid 99mTc-MIBI scintigraphy) and follow-up, AIT patients could be subdivided into six with AIT I, ten with AIT II and four with indefinite forms of AIT (AIT Ind). 99mTc-MIBI uptake results were normal/increased in all the six patients with AIT I and absent in all the ten patients with AIT II. The remaining four patients with AIT Ind showed low, patchy and persistent uptake in two cases and in the other two evident MIBI uptake followed by a rapid washout. MIBI scintigraphy was superior to all other diagnostic tools, including CFDS (suggestive of AIT I in three patients with AIT II and of AIT II in three with AIT Ind) and RAIU, which was measurable in all patients with AIT I, and also in four out of the ten with AIT II. Conclusion: Thyroid MIBI scintigraphy may be proposed as an easy and highly effective tool for the differential diagnosis of different forms of AIT