Etiologic study of primary congenital hypothyroidism.

The underlying causes of 35 children with primary congenital hypothyroidism at the Children's Hospital were studied. There were 21 girls and 14 boys. Serum T4 and TSH level, 24 hours 131I uptake, and technetium-99m thyroid scintigraphy were performed after discontinuation of synthetic thyroid hormone for 4-6 weeks. Athyrosis was the most common cause and accounted for forty-three per cent of the patients. Twenty per cent of the patients had thyroid hypoplasia. Ectopic thyroid was found in thirty-three per cent of the patients. Only a patient whose diagnosis was organification defect had slightly enlarged thyroid gland, high retention of 131I and positive perchlorate discharge test. Onset of symptoms before 9 months of age may be helpful for distinguishing between lingual thyroid and the others. Serum T4 level less than 2 micrograms/dL was observed to be more common in athyrosis and lingual thyroid groups than thyroid hypoplasia group.