What is the most likely result for this patient? A 4-year-old child whose family arrived in the United States from China last month is brought to the pediatrician for a checkup. On physical examination, the patient is found to be short, potbellied, and pale with a puffy face, a protruding umbilicus, and a protuberant tongue. The child shows clear signs of significant mental retardation.Upon questioning, the mother reveals that she did not suspect any abnormality because of many children in their village in China share the same appearance. The physician suspects thyroid abnormalities and orders a thyroid function test.

D

The correct answer is D. This patient is likely suffering from endemic cretinism due to a deficiency in dietary iodine, a disorder that is still common in parts of the world, including parts of China. Lack of dietary iodine leads to deficient thyroid hormone production and thus hypothyroidism. Thyroid hormone is critical during development and thus children who grow up in iodine-deficient areas may manifest skeletal and central nervous system abnormalities, including short stature and mental retardation. Unfortunately for this child, once the syndrome is clinically apparent, it cannot be reversed. Thyroid function tests detect the presence of TSH secreted by the pituitary gland, as well as circulating levels of total serum triiodothyronine (T3) and thyroxine (T4). T3 and T4 levels usually fluctuate in the same direction in most abnormalities, whereas the balance between TSH and T3/T4 levels helps determine the cause of the thyroid abnormality. In primary hypothyroidism, T3 and T4 levels will both be low, and a compensatory increase in pituitary activity will increase TSH Answer A is incorrect. These findings suggest an abnormality in the pituitary that is accounting for the hypothyroidism (such as a pituitary adenoma), reducing TSH production. Reduced TSH production, in turn, reduces production of triiodothyronine and thyroxine from the thyroid Answer B is incorrect. This combination of findings would be not be normally seen in patients Answer C is incorrect. These findings will be seen in patients with primary hyperparathyroidism, such as thyroid carcinoma or Graves disease. Due to autonomous production of triiodothyronine and thyroxine by the thyroid gland, there is a compensatory decrease in TSH production by the pituitary Answer E is incorrect. This combination of findings almost never occurs. It would theoretically suggest an abnormality in the terminal iodination step of thyroxine synthesis.