Congenital Hypothyroidism Due To Maternal Radioactive Iodine Exposure During Pregnancy

Abstract

Radioactive iodine (RAI) is used effectively in the treatment of hyperthyroidism and thyroid cancer, but it is contraindicated during pregnancy. RAI treatment during pregnancy can lead to fetal hypothyroidism, mental retardation and increased malignancy risk in the infant. Pregnancy tests must be performed before treatment in all women of reproductive age. However, at times, RAI is being used before ruling out pregnancy.We herein present a male newborn infant with congenital hypothyroidism whose mother was given a three-week course of methimazole therapy for her multiple hyperactive nodules and subsequently received 20 mCi RAI during the 12th week of her pregnancy. The patient was referred to our neonatology unit at age two weeks when his thyrotropin (TSH) level was reported to be high in the neonatal screening test. Physical examination was normal. Laboratory investigations revealed hypothyroidism (free triiodothyronine 1.55 pg/mL, free thyroxine 2.9 pg/mL, TSH 452 mU/L, thyroglobulin 20.1 ng/mL). The thyroid gland could not be visualized by ultrasonography. L-thyroxine treatment was initiated. Conflict of interest:None declared.

Case of radioactive iodine exposure during pregnancy

“…During human embryogenesis, the thyroid gland is developed, and it starts concentrating iodine and secreting iodotyrosine from 10-12 weeks of gestational age. 7,8 We suspect that in the present case, the fetal thyroid did not trap any I-131 because at the time of radiation, it did not concentrate iodine.…”

“…Kurtoğlu et al . reported a case in which an infant developed congenital hypothyroidism because the mother had received 20 mCi of radioactive iodine at 12 weeks of gestational age . In another report, the infant whose mother had received 103 mCi of I‐131 at 10 weeks of gestational age had thyroid tissue destruction .…”

“…The thyroid function of the infant (reference range) was as follows: thyroid-stimulating hormone levels (mIU/L) were 5.92 (3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22) at day 0, 2.91 (1-19) at day 5, and 2.37 (1-19) at day 28 and free thyroxine levels (pmol/L) were 15.45 at day 0, 26.64 at day 5, and 16.73 (7.47-21.1) at day 28. Thus, the infant's thyroid function test results revealed that the hormones were within their normal ranges after radiation exposure.…”

Acquired Hypothyroidism in an Adolescent Associated with Radioactive Iodine-131 Therapy of the Mother

“…Thyroid cancer was reported to develop in two adolescents receiving 131I MIBG therapy for neuroblastoma [4]. Cases of congenital hypothyroidism and thyroid cancer have been reported to develop following intrauterine exposure [2,3]. However, we encountered only one case of thyroid cancer developing in a child in close proximity to an individual receiving treatment [5].…”

“…All people, and particularly young children and pregnant women, are advised to avoid being in proximity to patients receiving this treatment. Cases of exposure in the prenatal period and the resultant development of congenital hypothyroidism and thyroid nodules have been widely reported in the literature [2,3]. Thyroid cancer has been reported in two adolescents receiving radioactive MIBG therapy, and there has been only one publication reporting papillary thyroid carcinoma developing as a result of 131I therapy administered to the mother [4,5].…”