EFFICACY OF LUGOL’S IODINE FOR THYROID BLOCKADE IN DIAGNOSTIC 131I MIBG SCAN.

Abstract

BACKGROUND: Radioiodine labelled Meta IodoBenzyl Guanidine (MIBG) is a noradrenaline analogue used for diagnosis and treatment of neuroendocrine tumor and there is high incidence of primary hypothyroidism after 131-I MIBG inspite of thyroid blockade. The aim of this study was to observe the efficacy of thyroid blockade in patients having diagnostic 131I MIBG scan. MATERIAL AND METHODS: This is a retrospective study conducted at Section of Nuclear Medicine, Department of Radiology, Aga Khan University Hospital, Karachi from 2004 till 2010. It includes all patients who were referred for a diagnostic 131I MIBG study. Patients were advised to start Lugol’s Iodine a day before test and subsequent 5 days to block the thyroid gland. 1mCi (0.9-1.2 mCi) of 131I MIBG was administered intravenously over 3-5 minutes followed by whole body image acquisition at 4, 24, 48, 72, 96 and 120 hours after injection. Images were analyzed for abnormal tracer deposition as well as thyroid uptake. Serum TSH level was found by checking hospital record (inside referral) and telephonic inquiry (outside referral). A serum TSH level >4 mU/l was considered suggestive of hypothyroidism. RESULTS: 31consecutive patients (M:F 19:12, Mean age: 28 years) who had diagnostic 131I MIBG scan from 2004-2010 were included. Ten scans revealed abnormal uptake over site of primary tumor or recurrence while thyroid uptake was not appreciated in any patient (4-120 hrs studies). Serum TSH level was available in 11 patients (performed 3 - 32 months after procedure) and were normal. CONCLUSION: We conclude that thyroid blockade using Lugol’s iodine in patients undergoing diagnostic 131I MIBG ensures complete thyroid blockade with no evidence of primary hypothyroidism.

Key words: MIBG, Hypothyroidism, Lugol’s Iodine, Pheochromocytoma, Neuroblastoma.