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Background and aims: The optimal dose of thyroxine (T4) in congenital hypothyroidism (CH) during infancy is controversial. Higher doses lead to improvement in cognitive scores, but have been linked to later behavioural difficulties. We have examined the effects of initial T4 dosage on somatic growth -- a putative surrogate marker of overtreatment. Methods: 314 CH children (214 girls, 100 boys) were analysed according to initial daily dose of T4: Group 1 (25 μg, n = 152), Group 2 (30-40 μg, n = 63) and Group 3 (50 μg, n = 99). Thyroid function and weight, length and occipito-frontal head circumference (OFC) standard deviation score (SDS) were compared at 3, 6, 12, 18, 24 and 36 months of age. Linear growth SDS was compared between the three groups using a regression adjustment model at 12 and 18 months of age using birth weight and 3-month data as baselines. Thyroid function was also compared at diagnosis (T0), and 7-21 days after the start of treatment (T1). Results: At T1 median thyroid stimulating hormone (TSH) for Groups 1, 2 and 3 was 58, 29 and 4.1 mU/l, respectively (p<0.001), Group 3 values remaining significantly lower at 3 and 6 months. Median free T4 (fT4) was within or just above the reference range in all groups at T1, but 7.4% of Group 1 had values <9 pmol/l compared with 5.1% and 0% for Groups 2 and 3, respectively. At 3 months weight, length and OFC SDS values were -0.39, -0.35, 0.09; -0.30, -0.47, 0.32; and -0.03, -0.13, 0.18 for Groups 1, 2 and 3, respectively, indicating relatively large OFC in all infants. A regression adjustment model showed no significant difference in growth rate from baseline and 12 or 18 months of age, between the three groups. Conclusion: An initial T4 dose of 50 [mu]g daily, normalises thyroid function several months earlier than lower-dose regimes, with no evidence of sustained somatic overgrowth between 3 months and 3 years. [ABSTRACT FROM AUTHOR]

Background: Thyroid imaging is helpful in confirming the diagnosis of congenital hypothyroidism and in establishing the aetiology. Although isotope scanning is the standard method of imaging, ultrasound assessment may be complementary. Aim: To determine the strengths and weaknesses of thyroid ultrasound and isotope scanning in neonates with thyroid stimulating hormone (TSH) elevation. Methods: Babies from the West of Scotland with raised capillary TSH (> 15 mU/l) on neonatal screening between January 1999 and 2004 were recruited. Thyroid dimensions were measured using ultrasonography, and volumes were calculated. Isotope scanning was carried out with a pinhole collimator after an intravenous injection of 99m-technetium pertechnetate. Results: 40 infants (29 female) underwent scanning at a median of 17 days (range 12 days to 15 months). The final diagnosis was athyreosis (n = 11 ), ectopia (n = 12), hypoplasia (n = 8; 3 cases of hemi-agenesis), dyshormonogenesis (n = 5), transient hypothyroidism (n = 2), transient hyperthyrotropinaemia (n = 1) and uncertain status with gland in situ (n = 1). 6 infants had discordant scans with no isotope uptake but visualisation of thyroid tissue on ultrasound. This was attributed to TSH suppression from thyroxine (n = 3); maternal blocking antibodies (n = 1 ); cystic degeneration of the thyroid (n = 1 ); and possible TSH receptor defect (n = 1 ). Conclusions: Isotope scanning was superior to ultrasound in the detection of ectopic tissue. However, ultrasound detected tissue that was not visualised on isotope scanning, and showed abnormalities of thyroid volume and morphology. We would therefore advocate dual scanning in newborns with TSH elevation as each modality provides different information. [ABSTRACT FROM AUTHOR]

Thyroid imaging has a role in the assessment of newborns with raised levels of thyroid stimulating hormone (TSH). In true congenital hypothyroidism, ultrasound may show no thyroid tissue in the neck because of either ectopia or agenesis. Alternatively the gland may be small in volume as the result of hypoplasia, or enlarged because of dyshormonogenesis, which is seen in 20% of our neonatal population with congenital hypothyroidism. In transient TSH elevation, associated with prematurity, acute illness, and congenital malformations, the thyroid gland should be of normal size.