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).
|Age (days)||T4 (1122 pmol/l)||TSH (0.35.0 mU/l)||FT3 (3.96.8 pmol/l)||Thyroxine replacement|
|16||28.3||22.9||Started on thyroxine 37.5 μg|
|24||31.2||6.0||Thyroxine reduced to 25 μg|
|40||27.9||6.5||7.5||Further reduction to 12.5 μg|
|50||22.2||9.4||7.2||Thyroxine 12.5 μg|
|60||21.1||10.9||7.4||Same dose as above|
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.
18 Sep 2014 - 20 Sep 2014