Case report of breastfeeding after maternal iodine contrast: neonatal hypothyroidism revealing an underlying congenital disorder

Abstract Background Iodine plays a critical role in producing thyroid hormones essential for brain development. An imbalance of iodine, whether deficiency or excess, can disrupt thyroid function. Iodine-induced hypothyroidism is rare but has been reported, particularly in premature infants exposed to excess iodine. Currently, iohexol, a nonionic radiocontrast agent, has limited data but is considered compatible with breastfeeding. Case presentation A small for gestation African American male neonate was born at 36 weeks and 3 days of gestation and admitted to the neonatal intensive care unit for respiratory distress and prematurity in the United States. Samples for Illinois newborn screens done at admission and repeated after 48 h of life were negative for thyroid abnormalities. On the infant’s fifth day of life, the mother underwent a contrast-enhanced imaging study using iohexol, after which the infant received breast milk from days 5–11. On day 11, the neonate had an elevated thyroid-stimulating hormone (TSH) and low free thyroxine (T4) levels, consistent with hypothyroidism. Urine iodine level in the infant was checked and found to be elevated, prompting concern for the exposure to iodine in breastmilk. However, the need to increase the levothyroxine dose to achieve normal thyroid levels was not consistent with a transient effect such as iodine exposure. Genetic testing revealed a likely pathogenic intragenic deletion in the gene RPS6KA3, consistent with Coffin–Lowry syndrome, as well as two variants of unknown significance (VUS) in IYD. Conclusions This case highlights the complex interplay between genetic factors and environmental influences in the development of neonatal hypothyroidism. While iodine contrast exposure through breast milk is generally considered safe, this case underscores the potential risks in preterm infants. Initially, iodine exposure through breastmilk was considered a likely contributor to thyroid dysfunction, but with further time and evaluation, congenital thyroid dysgenesis with underlying genetic findings complicated the diagnosis. This case demonstrates the importance of a comprehensive evaluation when working up thyroid dysfunction to exclude other potential etiologies before interrupting breastfeeding.