Introduction: Iodine is necessary for thyroid hormone synthesis, but when exposed to large quantities, iodine may have an inhibitory effect on hormone synthesis leading to hypothyroidism, known as the Wolff-Chaikoff effect. Newborns may be exposed to iodine through various events in early life. In 2012 three index cases with suspected iatrogenic hypothyroidism due to iodinated contrast exposure were discovered at the Neonatal department, The Queen Silvia Childrens Hospital, Gothenburg, Sweden. These three cases prompted us to regularly monitor thyroid function in patients who had been exposed to iodinated contrast via the gastrointestinal (GI) tract.
Method: Thyroid function was monitored in infants with gestational age ≤36 weeks at birth and exposed to iodinated contrast via the GI tract before 40 gestational weeks. We identified patients with elevated TSH (thyroid stimulating hormone). Patients with prolonged GI passage time were also identified. 73 patients born between June 2012 and December 2017 (48 males, 25 females) who met these criteria were identified.
Results: 33 patients (45%) had increased TSH levels after iodinated contrast exposure (9.2484 mU/l). Seven patients (9.5%) had both elevated TSH, and decreased f-T4 (thyroxine). Mean TSH was 53.9 mU/l. TSH was spontaneously normalized after mean 18 days in 8 infants who were not given levothyroxine treatment. In 8/11 (73%) infants who were given levothyroxine, TSH was normalized during treatment. In the remaining infants, we lack TSH-results post x-ray. We identified a few confounding factors. Three patients had Downs syndrome (9%) and four were born small for gestational age (SGA) (12%). 14/33 (42%) patients with elevated TSH had necrotizing enterocolitis (NEC). 28/33 (85%) patients with elevated TSH, had a prolonged GI passage time. In this material, we were not able to identify a specific gestational age where patients would be more susceptible to thyroid dysfunction after iodinated contrast exposure.
Conclusion: We found elevated TSH levels after exposure to iodinated contrast via the GI tract. The expected incidence of congenital hypothyroidism is usually 1/3000, which makes these cases evidently more common. Both prematurity and prolonged exposure time to iodine may be risk factors for iodine induced hypothyroidism. Even though this condition seems to be transient, follow-up studies are needed, especially investigations of cognitive outcome of these children. We suggest that thyroid function is investigated before and after exposure to iodine-containing contrast solutions.
27 - 29 Sep 2018
European Society for Paediatric Endocrinology