ODP447 A Case of Hidden Grave's After Total Thyroidectomy

INTRODUCTION: A Sub-sternal goiter is a condition where there is an abnormal enlargement of thyroid gland that extends into the chest. The most commonly accepted definition is when >50% of the volume of a goiter extends into the thoracic inlet. We present an interesting case of a Sub-sternal goiter emerging as a cause of Grave's disease, years after Total Thyroidectomy. CLINICAL CASE: The Patient is a 75 year old female with PMH of endometrial cancer, who initially underwent total thyroidectomy due to Thyromegaly causing dysphagia, and was started on Levothyroxine therapy after surgery. Three years later, a sub-sternal mass, was incidentally found via CT chest, which measured 3.7cm in largest diameter. Nuclear Medicine uptake and scan confirmed thyroid origin of this mass with an increased uptake but no percentage uptake was provided. Patient's Thyroid functions tests remained within normal range on levothyroxine. But over the next 2 years,the patient needed declining doses of LT4, then became euthyroid, off of levothyroxine and eventually became hyperthyroid, with positive Thyroid stimulating immunoglobulin. She also developed symptoms of tremors and tachycardia, and developed Atrial fibrillation as well. Noophthalmopathyor dermopathy was found on exam. Repeat CT chest showed the sub-sternal goiter had increased to a partially calcified mass of 5.6 cm. NM uptake scan showed 38.6%, at 24 hour, generalized uptake of this mass. Radioactive Iodine Ablation was performed with 30.1mCi and she subsequently became hypothyroid again until 1 year ago when she had episodes of A-fib again, and was found with TSH of 0. 09(0.45-5.33mIU/L) and FT40.9 (0.6- 1.2 ng/dl) and free T3 of 6.4 (pg/dl), off of levothyroxine. NM uptake and scan was repeated which indicated recurrence of Grave's disease from the same source. The Patient chose to initiate Methimazole therapy while contemplating surgical resection. Clinical Lesson: This is a unique case of Sub-sternal goiter, presenting as grave's disease, years after total thyroidectomy. This case emphasizes on the importance of identifying and treating sub-sternal goiter, as it can cause severe Grave's disease and thyrotoxicosis. Especially in this case, since Grave's caused by this sub-sternal goiter was recurrent after Radioactive iodine ablation. Presentation: No date and time listed