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A 29-day-old infant was referred by the newborn screening laboratory with mild but persistent capillary thyroid stimulating hormone (TSH) elevation: 11 mU/l on day 5 of life and 19.5 mU/l on day 23. He was born in the 39th week by planned caesarean section weighing 3814 g and was discharged home on day 3 without any health concerns. However, his mother had noticed a small lump on his neck which she took to be the baby's ‘Adam’s apple'.
Clinical examination was normal apart from a palpable lump in the upper neck located slightly to the right of the midline (figure 1). Neck ultrasound showed this to be an anvil-shaped, highly vascular homogenous structure measuring 0.9×1.1×1.3 cm, lying at and beneath the level of the base of the tongue (figure 2), and there was non-thyroidal tissue within the thyroid fossa.
Radioisotope scanning using 13 MBq pertechnetate showed uptake in the region of the oval structure, confirming the tissue to be thyroid. The infant was subsequently started on 25 μg of thyroxine and TSH dropped to 8.1 and 5.3 mU/l 7 and 28 days later, respectively. At 13 weeks of age, the lump in the neck was less prominent and ultrasound at 20 weeks showed significant reduction in vascularity of the ectopic thyroid, volume now 0.3 ml.
Since the TSH cut-off for newborn screening in Scotland was reduced from 25 to 8 mU/l we not infrequently encounter infants who have mildly elevated TSH and normal free T4.1 This scenario is often referred to as ‘hyperthyrotropinaemia’. However, there is no consensus concerning the follow-up and treatment plan for hyperthyrotropinaemia in infancy.
Tomita et al2 have previously described an infant with hyperthyrotropinaemia who was finally diagnosed as having definite congenital hypothyroidism due to ectopic thyroid at the age of 1.5 years. In our case the ectopic gland was low in site and thus visible but this is very unusual—most thyroid ectopia is sublingual, is not detectable clinically and may even be undetectable on ultrasound.3 The site of the thyroid tissue and the presence of non-thyroidal tissue in the thyroid fossa on neck ultrasound confirms that this was ectopia rather than a hypoplastic gland in situ.4 We conclude that it is always worthwhile carrying out thyroid imaging in infants with mild TSH elevation, and that the term ‘hyperthyrotropinaemia’ should be a diagnosis of exclusion.
Competing interests None.
Patient consent Obtained.
Provenance and peer review Not commissioned; externally peer reviewed.
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