ESPE Abstracts

Background: Trisomy 21 is associated with dysregulated pituitary thyroid axis with higher TSH and lower FT₄ than controls. This may be due to genomic imbalance from trisomy of chromosome 21. Transient congenital hypothyroidism (CH) in newborns is recognised in association with maternal thyroperoxidase (TPO) antibody positivity. ‘Thyroid hormone resistance’ in infancy in CH is also been described.

Objective and hypotheses: We report an interesting case of pituitary thyroid dysregulation with elevated plasma TSH and FT₄ in an infant with Trisomy 21.

Method: A term infant with Trisomy 21 was born to a mother with plasma TSH of 7 mU/l, FT₄ of 11 pmol/l and TPO positivity during the third trimester. He had FT₄ of 23.8 pmol/l and TSH 30.9 mU/l on day 10. TPO antibodies were absent. 99mTc-Pertechnetate scan showed uptake within a bilobed structure in the lower neck. Ultrasound scan showed normal appearance of the thyroid gland. Thyroxine replacement was started at 37.5 μg daily because of high TSH, persistent jaundice and widely open posterior fontanelle consistent with CH. TFT results are shown in Table below. The elevated plasma thyroid hormones failed to normalise plasma TSH.

Results: (Table 1).

Conclusion: The unusual thyroid function and its subsequent behaviour is consistent with combined thyroid hormone and TSH resistance in an infant with Down syndrome and CH.