This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Endocrinology, Subject name: Medicine
New born 7 days old with vomiting and dehydration clinical examination was normal except for hyperpigmentation of nipple. Electrolytes Na: 120 meq. K: 9 meq. mostlikelydiagnosis - 
Select and explain. 
A. Primary hypothyroidism, B. Cong, adrenal hyperplasia, C. Panhypopituitarism, D. Pyloric stenosis
B: Cong, adrenal hyperplasia
Answer: B: Cong, adrenal hyperplasia 
Explanation: Congenital adrenal hyperplasia due to defect in CYP21A2 is suggested by episodes of acute adrenal insufficiency with hyponatremia , hyperkalemia , dehydration & vomiting ( Harrison 17 pg 2267)