Severe Iodine Deficiency-Associated Hypothyroidism in a Toddler With Cow's Milk Allergy: A Case Report.

Abstract

Iodine is an essential micronutrient required for thyroid hormone synthesis and normal growth and neurodevelopment. Although iodine deficiency is uncommon in high-income countries with iodization programs, children with restrictive diets may remain at risk. We report a 23-month-old male who presented with growth deceleration and was found to have severe hypothyroidism. Initial laboratory evaluation demonstrated low FT4 with markedly elevated thyroid-stimulating hormone (> 200 mIU/L). Endocrine evaluation revealed diffuse thyroid enlargement with hypervascularity on ultrasonography and elevated thyroglobulin levels, with negative thyroid autoantibodies. Urinary iodine-to-creatinine ratio was low, consistent with iodine deficiency. Dietary review revealed multiple immunoglobulin E-mediated food allergies, including cow's milk allergy, and reliance on commercially available allergy-free foods lacking iodized salt. The patient was treated with levothyroxine, resulting in rapid normalization of thyroid function. Follow-up demonstrated improvement in urinary iodine levels and resolution of thyroid enlargement. This case highlights iodine deficiency as a reversible cause of severe hypothyroidism and growth delay in young children with restrictive diets. Clinicians should consider iodine deficiency in toddlers with food allergies and growth abnormalities, even in regions where iodine sufficiency is presumed.

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