Congenital hypothyroidism. Clinical and laboratory characteristics in infants detected by neonatal screening.

The clinical and laboratory characteristics of infants with neonatal hypothyroidism, and the age at which treatment was started are reviewed. The incidence of primary hypothyroidism was 1 in 3488 live births. Most of these cases were detected in a cord blood screening programme which was carried out between October 1973 and May 1980 in the Toronto region. Forty-eight infants with primary persistent hypothyroidism were classified by technetium scintiscanning as follows: 12 with athyrosis (non-visualised thyroid glands), 14 with ectopic thyroid glands, and 14 with goitrous thyroid glands. The remaining 8 infants comprised 4 with hypoplasia and 4 with transient hypothyroidism (2 idiopathic and 2 iodide induced). Although infants with athyrosis had a lower mean thyroxine value, their values overall were not significantly different from those of the other groups. Some infants, particularly those who were goitrous or ectopic, initially had normal thyroxine values. Skeletal maturation was more often delayed in athyrotic infants than in the ectopic or goitrous group. Radioactive iodine uptakes were appreciably higher in the goitrous group, and there was no significant difference between athyrotic and ectopic groups. The mean age at which treatment was started for all patients was 25 (range 6-120) days. The average age for starting treatment using initial thyroxine and secondary thyrotrophin testing in the initial stages of the cord blood screening was 36 days. The use of initial cord serum or dried blood thyrotrophin reduced the start of treatment to 14 days. It is concluded that: (1) It is important to determine the precise anatomical diagnosis, the biochemical severity, and the age at which treatment is started in order to assess the benefits of regional screening programmes in the detection of neonatal hypothyroidism. (2) Routine technetium scintiscanning before the start of treatment helps to determine the diagnosis. (3) Radioactive -I thyroid uptake studies are no longer routinely recommended; this is because of the radiation hazard and the lack of specificity in differentiating between the various anatomical types. (4) The feasibility of cord blood screening to detect the various causes of neonatal hypothyroidism is confirmed. (5) The time between final diagnosis and the institution of treatment can be reduced by 2 or 3 weeks if a thyrotrophin test is used initially from cord blood serum or, preferably, from dried blood spotted on filter paper; the latter is easier to post to a screening laboratory.