CAH

Q.) 3-week-old infant is admitted with vomiting of 5 days’ duration. Physical examination reveals a rapid heart rate, evidence of dehydration, and ambiguous genitalia. Serum electrolytes are Na+ 120 meq/L, K+ 7.5 meq/L, HCO3 − 12 meq/L, BUN 20 mg/dL. In addition to intravenous fluid replacement with normal saline, administration of which of the following would be most important?
(A) diuretics
(B) potassium exchange resin
(C) glucose and insulin
(D) antibiotics
(E) hydrocortisone

Ans:  (E) The child described probably has congenital adrenal hyperplasia (CAH), an inborn metabolic error of the adrenal cortex. The acidosis (HCO3 −12 meq/L) helps to rule out pyloric stenosis as the cause of the emesis, as most infants with pyloric stenosis have a metabolic alkalosis. The enzyme deficiency in CAH results in decreased production of cortisol and other adrenal cortical hormones and secondary hypertrophy of the adrenal gland. Accumulation of androgen-like precursors of cortisol during fetal development leads to masculinization of the female fetus and ambiguous genitalia, which is an important clue in this case. The low serumsodium and high serum potassium levels are classic findings in this condition, reflecting the lack of mineralocorticoids. In addition to the use of saline, administration of a mineralocorticoid such as cortisone or hydrocortisone is critical. The elevated serum potassium level usually responds rapidly to administration of saline and steroids, and specific therapy with exchange resins or glucose and insulin usually is unnecessary.

As did the preceding question, this question tests the examinee’s ability of recall rather

than recognition, a more difficult but clinically more relevant skill. Instead of providing a list of

diseases or syndromes as possible answers, it provides a list of additional features or findings, one of which is associated with the disorder in question. In this case, as in the preceding question, the feature to be selected is the appropriate therapy. The question tests more than the examinee’s ability to recite the treatment of hyperkalemia. It tests his or her ability to analyze the

clinical situation, make a correct diagnosis, set priorities, and tailor therapy to the specific

pathophysiology involved.