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Optimisation of thyroxine dose in congenital hypothyroidism
  1. P C Hindmarsh
  1. London Centre for Paediatric Endocrinology and Metabolism, Cobbold Laboratories, Middlesex Hospital, Mortimer Street, London W1T 3AA, UK
  1. Correspondence to:
    P C Hindmarsh
    (p.hindmarsh{at}ucl.ac.uk)

https://doi.org/10.1136/adc.86.2.73

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    Optimum initial dosage remains unclear

    The introduction of the screening programme for congenital hypothyroidism in the late 1970s and early 1980s has been rightly hailed as a major success in the prevention of neurological handicap. With a prevalence of between 1/3000 and 1/5000 live births, congenital hypothyroidism is by far the commonest metabolic disorder leading to neurological handicap; given the inexpensive nature of assays for thyroid stimulating hormone (TSH) and thyroxine treatment, its cost effectiveness must be beyond doubt. The improvement in outcome from intervention with thyroxine at an earlier stage than was hitherto possible, meant that for the majority of children treated with severe congenital hypothyroidism a near normal intelligence quotient (IQ) might be expected. Early reports tended to confirm this view, although a long term perspective suggests that there remain significant areas of cognitive deficit, particularly in visuospatial tasks, attention, and to a certain extent memory.1–3

    In addressing some of these issues several groups have suggested that early diagnosis combined with high thyroxine dosing can reverse this deficit and normalise IQ.

    OUTCOMES OF CURRENT INTERVENTION

    Neonatal screening and early replacement therapy with thyroxine has transformed the outlook for moderately affected (presenting total serum thyroxine concentrations greater than 40 nmol/l or presenting free thyroxine concentration greater than 5.5 pmol/l) individuals, normalising IQ at 5 and 10 years of age. Severely affected infants (presenting thyroxine less than 40 nmol/l), approximately 50% of the total, still develop a significant IQ deficit of approximately 10 points and may need special education.4,5 This may be related to hypothyroidism in utero, but several studies using higher doses of thyroxine in infancy in an uncontrolled manner have suggested that the effects of severe congenital hypothyroidism could be mitigated.6,7

    There are a number of problems associated with this approach. These largely relate to developmental …

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