Severe Thyrotoxicosis Following Topical Iodine Application

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Background: Exposure to iodine can lead to iodine-induced hyperthyroidism in patients with underlying thyroid disease. Clinical Case: A 67 year-old woman with a history of nontoxic multinodular goiter and atrial fibrillation presented with fatigue, palpitations, weight loss, and tremor. Laboratory evaluation demonstrated new-onset profound biochemical hyperthyroidism (FT4 > 7.77 ng/dL, n 0.8 – 1.8 ng/dL; FT3 >27.0 pg/mL, n 2.0-4.4 pg/mL). She was treated with beta-blocker, high doses of methimazole, and cholestyramine while further evaluation was pursued. She declined SSKI due to reported iodine allergy and steroids due to concerns about impact on wound healing following recent hip arthroplasty. TSI and TRAb were negative, and thyroid ultrasound showed stable nodules at 1.7cm. Pelvic ultrasound and MRI were obtained due to concern for non-thyroidal etiology, and revealed a 3.7cm septated cystic ovarian lesion, raising suspicion for struma ovarii. Whole body scan to localize site of thyroid hormone production could not be obtained due to high risk of clinical deterioration off methimazole, as she had persistent clinical and biochemical thyrotoxicosis on high doses (up to 90mg/day). She ultimately required 3 sessions of plasma exchange to lower her thyroid hormone levels, and then underwent bilateral salpingo-oophorectomy. Final pathology revealed mucinous cystadenoma without ectopic thyroid tissue. Post-operatively, her thyroid hormone levels were persistently elevated but improved compared to pre-operative levels, allowing for brief cessation of methimazole and completion of whole body scan. Imaging demonstrated a single focus of radioactive iodine uptake in the lower right thyroid lobe, correlating with the dominant 1.7 cm nodule on prior ultrasound, consistent with a toxic adenoma. Additionally, she was found to have an elevated urine iodine level (1200 mcg/24 hours, n 75 – 851 mcg/24 hours). Patient endorsed low iodine diet due to allergy history, and denied recent contrasted imaging study, dietary supplements, or amiodarone use. Upon further inquiry, she recalled using povidone-iodine solution to care for her surgical site post-arthroplasty, approximately a week before the onset of her initial symptoms. Her clinical presentation was ultimately attributed to toxic adenoma, with severe thyrotoxicosis exacerbated by iodine load. She underwent total thyroidectomy and is doing well on levothyroxine post-operatively. Conclusions: Topical iodine administration can contribute to iodine-induced hyperthyroidism in patients with underlying thyroid disease, and its use should be carefully considered in these patients. When evaluating a patient with new thyrotoxicosis, a detailed history of oral, IV, and topical iodine use should be obtained.