A newborn boy who was born at 39 weeks gestation by normal vaginal delivery has a serum TSH above the normal range and serum thyroxine (T4) below the normal range for his age. His mother has no medical conditions. On examination, the patient's length and weight are normal, and he has no apparent congenital malformations. Which of the following is the most likely cause of this patient's condition?

Question

A newborn boy who was born at 39 weeks gestation by normal vaginal delivery has a serum TSH above the normal range and serum thyroxine (T4) below the normal range for his age.  His mother has no medical conditions.  On examination, the patient's length and weight are normal, and he has no apparent congenital malformations.  Which of the following is the most likely cause of this patient's condition?

Quizplus · Accepted Answer

11ec160b_3ac3_1fbe_9249_794c700ea704_MD0001_00 This patient has primary hypothyroidism, a congenital condition most commonly caused by thyroid dysgenesis. Thyroid dysgenesis refers to an underdeveloped thyroid (ie, hypoplasia, aplasia) or an ectopic thyroid, which can lie anywhere along the normal path of embryologic descent from the base of the tongue to its normal location anterior to the thyroid cartilage. Most cases are sporadic and isolated without other congenital abnormalities. Newborns are usually asymptomatic due to the transplacental transfer of maternal thyroxine (T4), although levels are decreased compared to those of healthy patients. Because of insufficient feedback inhibition from low T4 levels, TSH is elevated. Newborn screening allows for early identification and treatment with levothyroxine, which prevents the development of neurocognitive dysfunction. (Choice A) Hypothalamic or pituitary dysfunction can lead to central hypothyroidism due to deficient TSH production. TSH and T4 levels would both be low. (Choice B) Congenital hypothyroidism can also be caused by thyroid hormone resistance (eg, thyroid hormone receptor mutations). However, TSH and T4 levels would be elevated due to impaired thyroid hormone feedback. (Choice C) Thyroid-binding globulin (TBG) is a transport protein that binds T4. TBG deficiency results in a euthyroid state characterized by a low level of total T4 but normal TSH and free T4 levels. (Choice E) Neonatal Graves disease is characterized by the transplacental transfer of maternal TSH receptor-stimulating antibodies due to maternal Graves disease. This condition causes transient hyperthyroidism with elevated T4 and decreased TSH. Educational objective: Thyroid dysgenesis (ie, hypoplasia, aplasia, ectopy) is the most common cause of primary congenital hypothyroidism. In this condition, TSH is elevated and thyroxine (T4) is low. __________ References: Congenital hypothyroidism. (http://www.ncbi.nlm.nih.gov/pubmed/32644339)

A Newborn Boy Who Was Born at 39 Weeks Gestation