Iodine-induced hypothyroidism in full-term infants with congenital heart disease: more common than currently appreciated?

CONTEXT: Iodine is a micronutrient essential for thyroid hormone synthesis. Thyroid hormone is critical for normal neurocognitive development in young infants, and even transient hypothyroidism can cause adverse neurodevelopmental outcomes. Both iodine deficiency and excess can cause hypothyroidism. Although iodine-induced hypothyroidism is well recognized in premature infants, full-term neonates have received less attention. Infants with congenital heart disease (CHD) are commonly exposed to excess iodine from administration of iodinated contrast agents during cardiac catheterization as well as topical application of iodine-containing antiseptics and dressings; hence, this is a vulnerable population.
OBJECTIVE: We report three cases of iodine-induced hypothyroidism in full-term neonates with CHD after cardiac angiography and topical application of iodine-containing antiseptics and dressings in the operative setting.
RESULTS: Three neonates with CHD and normal thyroid function at birth developed hypothyroidism after exposure to excess iodine. Two of these infants had transient hypothyroidism, and one had severe hypothyroidism requiring ongoing thyroid replacement therapy. All infants were asymptomatic, with hypothyroidism detected incidentally in the inpatient setting due to repeat newborn screening mandated by the long duration of hospitalization in these infants.
CONCLUSIONS: Iodine-induced hypothyroidism may be under-recognized in infants with CHD exposed to excess iodine. Systematic monitoring of thyroid function should be considered to avoid potential long-term adverse neurodevelopmental effects of even transient thyroid dysfunction in this susceptible population.