Scintigraphic evaluation of primary congenital hypothyroidism: results of the Greek screening program

The Greek screening program for primary congenital hypothyroidism was initiated in 1979. By early 2000, thyrotropin measurements had been performed in 1,976,719 newborns, using dried blood spots obtained by heel prick. Among these children, 584 were diagnosed with congenital hypothyroidism (incidence: 1/3,384 births) and were given L-thyroxine (L-T4) replacement therapy. In order to further evaluate and classify the children as having either an aplastic (AT) or an ectopic thyroid gland (ET) or as showing thyroidal dyshormonogenesis (DN, with a nomotopic gland), scintigraphic studies were performed at the age of 2-3 years. In 413 children of this age group (including 24 subsequently diagnosed as having had transient hypothyroidism, in whom L-T4 therapy was not resumed), thyroid hormones were measured and scintigraphic studies were done after withdrawal of L-T4 replacement treatment for 3 weeks. Given the long duration of the study, we used various scintigraphic modalities. In 96 children (group A), scintigraphy was performed using technetium-99m pertechnetate (99mTcO4-; 18.5 MBq given i.v.) and a rectilinear scanner. Seventy-three children (group B) were studied with 99mTcO4- (18.5 MBq given i.v.) and a gamma camera equipped with a pinhole collimator. In these groups, atropine was administered 30 min prior to the study (0.02 mg/kg i.v. or i.m.) in order to reduce the secretion of saliva from the salivary glands. Finally, in the remaining 220 children (group C) iodine-123 sodium iodide (123I-Na) (0.74-1.85 MBq i.v.) and the same gamma camera were used. Between-group comparisons of scintigraphic findings were done with the chi square test. In 191 children from group C, thyroglobulin (Tg) was measured and in 49 children ultrasound (US) was performed (categorising the gland as AT or ET/DN). Comparison of these modalities was done with the kappa statistic. In group A, 61.5% of children had AT, 26.0% had ET and 12.5% had DN; in group B, 28.8% of children had AT, 52.0% had ET and 19.2% had DN; in group C, 23.2% of children had AT, 63.2% had ET and 13.6% had DN. Statistically significant differences in group A versus groups B and C were noted for AT and ET. The implementation of newer scintigraphic modalities, and especially the use of 123I-Na, indicates that the commonest finding in congenital hypothyroidism is ET. Scintigraphy was more concordant with Tg measurements (though at a moderate level) than with US. The latter was even less concordant with Tg values. These results show that the most appropriate approach for the evaluation and classification of congenital hypothyroidism is 123I-Na scanning.