Evaluation of 99m Tc-MIBI in thyroid gland imaging for the diagnosis of amiodarone-induced thyrotoxicosis.

OBJECTIVE: Amiodarone-induced thyrotoxicosis (AIT) is caused by amiodarone as a side effect of cardiovascular disease treatment. Based on the differences in their pathological and physiological mechanisms, many methods have been developed so far to differentiate AIT subtypes such as colour flow Doppler sonography (CFDS) and 24-h radioiodine uptake (RAIU). However, these methods suffer from inadequate accuracy in distinguishing different types of AITs and sometimes lead to misdiagnosis and delayed treatments. Therefore, there is an unmet demand for an efficient method for accurate classification of AIT.

METHODS: Technetium-99 methoxyisobutylisonitrile (99m Tc-MIBI) thyroid imaging was performed on 15 patients for AIT classification, and the results were compared with other conventional methods such as CFDS, RAIU and 99m TcO4 imaging.

RESULTS: High uptake and retention of MIBI in thyroid tissue is characteristic in Type I AIT, while in sharp contrast, low uptake of MIBI in the thyroid tissue was observed in Type II AIT. Mixed-type AIT shows uptake value between Types I and II. MIBI imaging outperforms other methods with a lower misdiagnosis rate.

CONCLUSION: Among the methods evaluated, MIBI imaging enables an accurate identification of Type I, II and mixed-type AITs by showing distinct images for different types of AITs. The results obtained from our selected subjects revealed that MIBI imaging is a reliable method for diagnosis and classification of AITs and MIBI imaging has potential in the treatment of thyroid diseases. Advances in knowledge: 99m Tc-MIBI imaging is a useful method for the diagnosis of AIT. It can distinguish different types of AITs especially for mixed-type AIT, which is usually difficult to treat. 99m Tc-MIBI has potential advantages over conventional methods in the efficient treatment of AIT.