ESPE Abstracts

Background: Infants referred with elevation of capillary TSH on newborn screening are classified as having transient TSH elevation when subsequently found to have normal venous thyroid function tests off treatment with thyroxine. Causes of transient TSH elevation include neonatal sickness, prematurity and maternal thyroid antibodies. There is little information on thyroid size in such infants.

Objective: To determine thyroid volume by ultrasound in infants with transient TSH elevation.

Hypothesis: That most subjects would show normal volume glands compared with population-specific data.

Method: Two observers rated thyroid size by subjective evaluation (Sx) as small, small-normal, normal, large-normal and large, and then reached consensus where possible. On two separate occasions the observers measured volume of each lobe by objective evaluation (Ox) according to the formula length x breadth x depth x π/6 and deriving total gland volume as the sum of both lobes. Given population-specific mean (SD) volume of 1.61 (0.4) ml, Ox volumes corresponding to Sx were set at <0.8, 0.8–1.0, >1−<2.2, 2.2–2.4, and >2.4 ml.

Results: Images from 15 infants (M: F=9:6), median (range) birthweight 3.06 (2.37–3.8)kg and gestation 39 (33–42) weeks were available for study. Three infants were scored as having large glands on Sx, with Ox volume 2.42 ml in one (Pendrin heterozygote) but 1.8 and 0.85 ml in the other two. One infant who was sick at birth due to placental abruption and renal failure had a normal gland on both Sx and Ox (volume 1.17 ml). Sx and Ox assessment was not possible in a further infant with allo-immune thyroiditis causing peri-thyroidal oedema. Of the remaining 10 infants Ox volume was <0.8 (range 0.48–0.76) ml in 8; and 0.82, 0.83 ml in the other two, Sx evaluation normal in 6 and small-normal in 4. Uptake of radioisotope was decreased in 5 and absent in 2 of these infants. Transient TSH elevation was attributable to blocking antibodies (3), heterozygous TSH receptor mutation (1) and cause unknown (6).

Conclusion: Thyroid volume in infants with transient TSH elevation was unexpectedly reduced on objective measurement in 10/15 patients in our series. This emphasises the importance of careful Ox evaluation, and raises the question as to whether follow up with repeat thyroid function testing and imaging later in childhood might be more appropriate than discharge from clinic in “transient” cases.