Severe hypothyroidism following a single topical exposure to iodine in a premature neonate

A neonate, born at 24 weeks, underwent a patent ductus arteriosus ligation, with previous normal thyroid stimulating hormone (TSH) levels, developed severe hypothyroidism from topical exposure to iodine following a single surgical procedure at 28 days of life. A low free T4 level of 0.05 ng/dL and a high TSH level of 228 mIU/L was detected with an increased urinary iodine excretion level of 178 mg/L (reference range 0.30-1.97 mg/L). The thyroid ultrasound was normal. Levothyroxine was started immediately but thyroid function did not recover fully during admission and levothyroxine was required beyond term corrected. This case highlighted how susceptible extremely preterm infants are to iodine induced hypothyroidism, even short-term topical exposure. Delayed treatment of hypothyroidism can lead to profound neurodevelopmental delay. As surgical advances allow for interventions at earlier gestations, the importance of early thyroid function testing postexposure to iodine is highlighted and ultimately topical iodine should be avoided in these susceptible infants.