An 8-day-old male infant is brought to the emergency department with vomiting, lethargy, dehydration and features of shock. Clinical examination reveals hyperpigmentation of the genital skin and normal external genitalia. Blood investigations reveal Sodium 124 mEq/L, potassium of 7 mEq/L and hypoglycemia. Which of the following is the most likely diagnosis?

## **Core Concept**
The clinical presentation of an 8-day-old male infant with vomiting, lethargy, dehydration, features of shock, hyperpigmentation of the genital skin, hyponatremia, hyperkalemia, and hypoglycemia suggests an adrenal crisis. The symptoms point towards a condition affecting the adrenal glands, leading to a deficiency of adrenal hormones.

## **Why the Correct Answer is Right**
The correct answer, **Congenital Adrenal Hyperplasia (CAH)**, specifically the salt-wasting form, is a genetic disorder that affects the adrenal glands. It leads to a deficiency of the enzyme 21-hydroxylase, which is crucial for the synthesis of cortisol and aldosterone from cholesterol in the adrenal cortex. The deficiency results in decreased production of aldosterone (leading to salt-wasting and dehydration) and cortisol (leading to increased ACTH levels, which cause adrenal hyperplasia and hyperpigmentation). The increased ACTH also leads to an overproduction of androgens, causing virilization. However, in this case, the external genitalia are normal, but the hyperpigmentation of the genital skin suggests increased androgen effect.

## **Why Each Wrong Option is Incorrect**
- **Option A:** This option is incorrect because while it might seem related, the specific clinical presentation and biochemical abnormalities point more specifically to CAH.
- **Option B:** This option does not directly relate to the clinical presentation of adrenal crisis with electrolyte imbalance and hyperpigmentation.
- **Option C:** This option, like option B, does not directly correlate with the symptoms and lab findings presented.

## **Clinical Pearl / High-Yield Fact**
A key clinical pearl is that Congenital Adrenal Hyperplasia can present with salt-wasting crisis in the neonatal period, characterized by vomiting, dehydration, shock, hyponatremia, hyperkalemia, and hypoglycemia. Hyperpigmentation, particularly of the genital area, and normal external genitalia in a male infant should raise suspicion for CAH. Early diagnosis and treatment are critical to prevent mortality.

## **Correct Answer: C. Congenital Adrenal Hyperplasia.**

✓ Correct Answer: A. Congenital Adrenal Hyperplasia (CAH)