A week-old boy is brought to the emergency department due to vomiting and poor feeding. His mother received appropriate prenatal care, and the full-term infant was delivered at home. Temperature is 36.7 C (98 F), blood pressure is 40/24 mm Hg, pulse is 164/min, and respirations are 46/min. Physical examination is notable for sunken eyes, a depressed anterior fontanelle, and dry mucous membranes. Capillary refill is 3 seconds, and skin turgor is decreased. No abdominal masses are noted. Genital examination shows a normal uncircumcised penis with bilateral testes palpable in the scrotum. Laboratory results are as follows: Which of the following is most likely to be increased in this patient?

Question

A week-old boy is brought to the emergency department due to vomiting and poor feeding.  His mother received appropriate prenatal care, and the full-term infant was delivered at home.  Temperature is 36.7 C (98 F), blood pressure is 40/24 mm Hg, pulse is 164/min, and respirations are 46/min.  Physical examination is notable for sunken eyes, a depressed anterior fontanelle, and dry mucous membranes.  Capillary refill is 3 seconds, and skin turgor is decreased.  No abdominal masses are noted.  Genital examination shows a normal uncircumcised penis with bilateral testes palpable in the scrotum.  Laboratory results are as follows:  Which of the following is most likely to be increased in this patient?

Quizplus · Accepted Answer

Explanation: 11ec25c8_d65a_6ceb_bc81_d9a6b9a151fb_MD0003_00 This infant has classic congenital adrenal hyperplasia (CAH) caused by 21-hydroxylase deficiency, which results in: Inhibited conversion of progesterone to 11-deoxycorticosterone, a precursor to aldosterone: Decreased aldosterone causes dehydration (eg, sunken fontanelle, dry mucosa) and salt-wasting (eg, hypotension, hyponatremia, hyperkalemia) (Choices A and C). Inhibited conversion of 17-hydroxyprogesterone to 11-deoxycortisol, a precursor to cortisol: Decreased cortisol results in fasting hypoglycemia (Choice D). Increased conversion of 17-hydroxyprogesterone to androstenedione, a precursor to testosterone: Increased testosterone causes virilization and ambiguous genitalia in female infants. Male infants typically have no abnormal newborn genital findings, although they may have an enlarged penis or scrotal hyperpigmentation. Newborn screening allows early detection of classic CAH, and a significantly elevated 17-hydroxyprogesterone level confirms the diagnosis. Treatment involves glucocorticoid and mineralocorticoid replacement. (Choice E) LH is decreased in patients with classic CAH as elevated testosterone provides negative feedback to the hypothalamic-pituitary axis and inhibits LH secretion. Educational objective: Deficiency of 21-hydroxylase is the most common cause of congenital adrenal hyperplasia and classically presents with dehydration, salt-wasting, and virilization. Elevated 17-hydroxyprogesterone levels are diagnostic. References: Diagnosis and management of classical congenital adrenal hyperplasia. (http://www.ncbi.nlm.nih.gov/pubmed/23624029)

A Week-Old Boy Is Brought to the Emergency Department Due