MON-453 Iodine-Induced Thyrotoxicosis Leading to Severe Osteoporosis: A Case Report

Abstract Disclosure: S. Vallejo: None. J. Shakil: None. S. Dowlatshahi: None. Introduction: Maintaining euthyroid status is crucial for skeletal health, as elevated thyroid hormones accelerate bone loss, leading to decreased bone mineral density (BMD) and increased fracture risk. While most individuals tolerate high iodine intake, excessive iodine can induce thyrotoxicosis in susceptible individuals. Common sources include iodized salt, amiodarone, and seaweed-based supplements such as kelp. We report a case of iodine-induced thyrotoxicosis secondary to kelp consumption, resulting in severe osteoporosis, emphasizing the importance of dietary awareness in thyroid management. Case: A 58-year-old woman with osteoporosis, low BMI, and premature ovarian insufficiency (POI) was evaluated for worsening bone density despite prior treatment with alendronate. Initial BMD revealed the lowest T-score of -2.6. Laboratory evaluation showed: TSH <0.005 mIU/L, FT4: 7.14 ng/dL. FT3: 6.1 pg/dL, Calcium: 10.5 mg/dL, Albumin: 4.1 g/dL, PTH: 21 pg/mL. She had no thyroid disease history or relevant medication use. Physical exam was unremarkable. A whole-body I-123 scan showed decreased thyroid uptake, suggesting subacute thyroiditis. She was advised to avoid excessive iodine and was treated with prednisone. She also started denosumab but was lost to follow-up. Two years later, she presented with tremors, palpitations, and persistent thyrotoxicosis: FT4: 5.34 ng/dL, FT3: 7.0 pg/dL, TSH: <0.005 mIU/L, TSI: <0.10 IU/L, TRAb: <1.10 IU/L, Thyroglobulin: 5.4 ng/mL. Ultrasound showed an atrophic thyroid gland. A Tc-99m pertechnetate scan ruled out increased uptake or ectopic thyroid tissue. A repeat BMD showed worsening osteoporosis (T-score -3.0).Dietary history revealed substantial kelp supplement use, indicating chronic iodine excess. While POI contributes to osteoporosis, her worsening BMD corresponded with persistent thyrotoxicosis, suggesting iodine-induced thyrotoxicosis as the primary factor. Nutritional counseling and psychiatric assessment were recommended to evaluate behavioral factors contributing to excessive supplement use. Discussion: Excess iodine can overwhelm thyroid adaptation (Jod-Basedow effect), causing thyrotoxicosis, particularly in susceptible individuals. Beyond cardiovascular effects, prolonged thyrotoxicosis accelerates bone loss, exacerbating osteoporosis. Kelp and similar supplements can exceed the recommended iodine intake of 1,100 mcg/day, necessitating dietary education.This case highlights the difficulty of managing iodine-induced thyrotoxicosis, especially when unrecognized supplement intake is involved. Comprehensive care should include dietary counseling and, when needed, psychiatric evaluation to address behavioral patterns contributing to excessive supplement use and related health risks. Presentation: Monday, July 14, 2025