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 μg/dL was observed to be more common in athyrosis and lingual thyroid groups than thyroid hypoplasia group.