Endocrine Abstracts

Background: In adults, hypoparathyroidism is a rare, but recognised complication of radioactive Iodine therapy. Hypothyroidism has been reported in neonates who have been exposed to Iodine¹³¹ in-utero, however, only one case of neonatal hypoparathyroidism secondary to maternal Iodine¹³¹ therapy has been described in the literature. To our knowledge this is the first case in the UK.

Case presentation: A 27-year-old woman received two doses of Iodine¹³¹ therapy following total thyroidectomy for thyroid carcinoma. The first dose was given approximately 3 months prior to conception and the second dose at an estimated 10–12 weeks gestation. The mother was on 200 mcg levothyroxine at the end of pregnancy. The infant was born weighing 3400 g at 39 weeks gestation with severe clinical and biochemical features of hypothyroidism, (capillary TSH >150 mU/l on day 1 of life, 268 mU/l day 6). She was normocalcaemic on day 1 (2.21 mmol/l) but became hypocalcaemic by day 2 (1.43 mmol/l, PTH <1.2 pmol/l), with normal vitamin D levels. Initial treatment was with levothyroroxine (25 mcg) and calcium alone. Plasma calcium normalised; supplements were reduced then discontinued (day 25) with ongoing monitoring. She became hypocalcaemic again (day 37) and 1 Alpha Calcidol was commenced. At 6 weeks of age the patient had a cardio-respiratory arrest following RSV positive bronchiolitis and hypocalcaemia. She continued to have refractory hypocalcaemia despite increasing calcium and vitamin D supplementation. There was evidence of ‘seizures’ and possible tetany, although the cause was unclear – hypocalcaemia or CNS ischaemic insult – and the child was left with severe neurological impairment.

Conclusion: Radioactive Iodine¹³¹ may occasionally be given inadvertently to pregnant women despite rigorous protocols in place to prevent such an occurrence. Whilst Iodine¹³¹ is known to have an impact on thyroid tissue, the parathyroid glands can also be affected. The severity of this infant’s hypothyroidism also questions maternal compliance with her own thyroxine medication. Neonatal hypoparathyroidism is a very rare complication of radioactive Iodine¹³¹ during pregnancy. Monitoring of both thyroid and parathyroid function in at-risk infants after birth is recommended.