Endocrine Abstracts

Introduction: Thyroid carcinoma (TC) is the most common endocrine malignancy. Although the overall prognosis for patients with TC is good, up to 20% of patients develop recurrent or persistent disease after conventional therapy by total thyroidectomy and radioactive iodine (RAI). Amiodarone is a highly efficient anti-arrhythmic drug with a very long half-life, so it may interfere with RAI many months after the drug withdrawal. This case report mirrors the challenges of thyroid cancer management in an amiodarone treated patient.

Case: A 65 years-old man, with a well-differentiated papillary cancer (T3N1aMx), underwent total thyroidectomy in 2013, followed by RAI therapy. The I 131-whole body scan (WBS) failed to indicate uptake, in discordance to high TG levels 927.4 ng/ml and low Tg Ab 26 IU/ml and presence of lateral cervical lymph nodes at ultrasound (US). In view of prior use of amiodarone for the past 2 years, which was interrupted 6 weeks before RAI therapy and negative WBS, in March 2014 the serum amiodarone concentration was <0.01 mg, but associated with high serum 192 μg/l and urinary iodine 782 μg/levels, showing excessive iodine body load. The head,neck and thorax CT scan were negative, despite the abnormal TG 393.3 ng/ml. 18FDG-PET showed left latero-cervical and supraclavicular lymphadenopathy, and no distant metastases. In July 2014, TG increased to 863 ng/ml and therefore, the patient received an additional dose of 76.4 mCi I 131. The post-therapeutic WBS showed RAI uptake in the neck. In October 2014 the Tg level was still elevated at 1105 ng/ml, so the patient received another completion dose of 118.8 mCi I 131, followed in March 2015 by another dose of 100 mCi I 131, at a Tg level of 766 ng/ml. Pathological lymph node uptake was confirmed at WBS and no uptake in the thyroid bed or distant secondary disease was evidenced. Neck US confirmed multiple left latero-cervical and supraclavicular round, hypo-echoic, intensely, vascularized lymphadenopathies. In view of lack of adequate response of the disease to RAI treatment, and no organic metastases, the patient was proposed to therapeutic lymph node dissection.

Discussion: In high amounts, iodine saturates the thyroid gland, blocking further absorption of both non-radioactive and radioactive iodine. As in the presented case, iodine uptake blockade is prolonged for several months after high iodine exposure by amiodarone intake and may explain lack of RAI image on WBS in our patient, despite increased Tg levels and US data.