Hypothyroidism and Goiter in a Young Male with Suspected Dietary Iodine Deficiency Followed by Thyrotoxicosis After Iodine Supplementation

ABSTRACT Objective Iodine deficiency disorders (IDDs) remain a major public health concern in most parts of the world but are extremely rare in North America. We describe a case of goiter in a young male with dietary history and findings suggestive of IDD. Methods Laboratory and imaging procedures including thyroid function tests, autoantibodies, urine iodine, thyroid ultrasound, and radioactive iodine (RAI) uptake scan were performed. Results On initial presentation, thyroid-stimulating hormone (TSH) was 24.4 mIU/L (normal range is 0.4 to 5.0 mIU/L), free thyroxine was <0.4 ng/dL (normal range is 0.8 to 1.8 ng/dL), and thyroid peroxidase antibody was positive at 43 IU/mL (normal range is <35 IU/mL). He reported consuming strawberries and peanut butter sandwiches with no intake of dairy or seafood due to gastrointestinal issues (abdominal pain, bloating, and nausea). Physical exam revealed a diffusely enlarged, palpable thyroid gland (grade II goiter). Ultrasound of the neck showed an enlarged thyroid gland with no nodules. RAI uptake scan showed diffuse increased uptake (91%). Given his poor diet, a 24-hour urinary iodine excretion test was ordered which was suggestive of very low iodine intake. He was started on multivitamins with 150 μg of iodine daily. On follow up, clinical exam showed grade I goiter and TSH had normalized to 0.7 mIU/L and free thyroxine was 1.2 ng/dL. He continued on iodine supplementation and tolerated iodine-rich foods. Six months later, thyroid function tests showed hyperthyroidism with TSH of <0.002 ng/dL and free thyroxine was elevated to 2.8 ng/dL. Iodine supplements were stopped. Conclusion Hypothyroidism and goiter due to IDD should be suspected in the setting of poor dietary intake. IDDs can be rapidly diagnosed in a patient on a restricted diet with multiple urinary iodine determinations and RAI study. Regular thyroid labs should be done to monitor for hyperthyroidism that can develop after iodine supplementation.