A 1-week-old boy is brought to the emergency department due to recurrent vomiting and poor feeding. The infant was born at term via spontaneous vaginal delivery with no complications. Temperature is 36.7 C (98 F), blood pressure is 58/30 mm Hg, pulse is 180/min, and respirations are 40/min. On examination, the patient is tired appearing with a sunken anterior fontanelle and dry mucous membranes. The remainder of the examination is unremarkable. Laboratory results are as follows:
| Serum chemistry | |
| Sodium | 122 mEq/L |
| Potassium | 5.7 mEq/L |
| Blood urea nitrogen | 25 mg/dL |
| Creatinine | 0.6 mg/dL |
Which of the following additional laboratory findings are most likely to be seen in this patient?
Show Explanatory Sources
This infant is dehydrated (ie, sunken fontanelle, dry mucous membranes) with hypotension, hyponatremia, and hyperkalemia. These findings are consistent with classic congenital adrenal hyperplasia (CAH) due to 21-hydroxylase deficiency.
Patients with 21-hydroxylase deficiency cannot convert 17-hydroxyprogesterone (17-OHP) into 11-deoxycortisol, which results in elevated 17-OHP and decreased aldosterone and cortisol production. Corticosteroid precursors accumulate and are diverted toward excess adrenal androgen biosynthesis. Low cortisol levels (ie, loss of negative feedback) also trigger increased ACTH production by the anterior pituitary, which further stimulates the formation of adrenal androgens (Choice D).
Although affected girls are usually identified at birth due to ambiguous genitalia (virilization) from excess androgens, boys have normal genitalia and typically are identified at age 1-2 weeks with vomiting, hypotension, hyponatremia, and hyperkalemia due to lack of sufficient mineralocorticoids (salt wasting). Cortisol deficiency causes hypoglycemia and further impairs the ability to maintain blood pressure.
(Choice B) CAH due to 17 alpha-hydroxylase deficiency prevents the conversion of progesterone to 17-OHP, resulting in low 17-OHP, cortisol, and adrenal androgen production. In contrast to this case, hypertension and hypokalemia occur with 17 alpha-hydroxylase deficiency due to increased mineralocorticoids.
(Choice C) Adrenal steroid synthesis is also impaired with primary adrenal insufficiency (ie, Addison disease); however, autoimmune destruction of the adrenal glands is unlikely to occur in the first week of life, making 21-hydroxylase deficiency a much more likely cause of adrenal crisis in this patient.
(Choice E) An ACTH-secreting tumor causes increased synthesis of cortisol and its precursors (eg, 17-OHP). Cushing disease is rare in newborns and would be associated with glucocorticoid-induced hypertension (not hypotension) and subsequent inhibition of aldosterone.
Educational objective:
Classic 21-hydroxylase deficiency causes decreased cortisol and aldosterone production with increased adrenal androgen production. In boys, this deficiency presents 1-2 weeks after birth with vomiting, hypotension, hyponatremia, and hyperkalemia due to salt wasting; genitalia are normal. In girls, it presents at birth with ambiguous genitalia.