Examkin

Question

Difficulty: Very hardPediatric Endocrine Disorders

A 4-day-old male infant is brought to the emergency department due to poor feeding, excessive sleepiness, and jittery movements. He was born at 39 weeks of gestation via uncomplicated vaginal delivery to a 28-year-old primigravid mother. Vital signs show a temperature of 36.1°C (97.0°F), heart rate of 165/min, respiratory rate of 45/min, and blood pressure of 58/36 mmHg. Physical examination reveals a lethargic neonate with mild scleral icterus. Genitourinary examination shows bilateral nonpalpable testes and a stretched penile length of 1.4 cm (normal for term > 2.5 cm). Laboratory studies reveal a capillary blood glucose of 34 mg/dL. He is given an intravenous dextrose bolus with improvement in his symptoms. Additional laboratory results are as follows:

Laboratory TestResultReference Range
Sodium132 mEq/L135-145 mEq/L
Potassium4.2 mEq/L3.5-5.5 mEq/L
Chloride98 mEq/L98-106 mEq/L
Bicarbonate20 mEq/L20-28 mEq/L

Which of the following is the most likely diagnosis?

  1. Congenital hypopituitarismAnswer
  2. B
    21-hydroxylase deficiency
  3. C
    3-beta-hydroxysteroid dehydrogenase deficiency
  4. D
    5-alpha-reductase deficiency
  5. E
    Complete androgen insensitivity syndrome

Answer

Congenital hypopituitarism
The correct answer is congenital hypopituitarism. This patient presents with panhypopituitarism, which classically manifests in the neonatal period with a triad of hypoglycemia (due to growth hormone and adrenocorticotropic hormone [ACTH] deficiency), micropenis with cryptorchidism (due to luteinizing hormone [LH] and follicle-stimulating hormone [FSH] deficiency), and prolonged jaundice (due to thyroid-stimulating hormone [TSH] deficiency). The laboratory findings show hypoglycemia and hyponatremia. Hyponatremia occurs because cortisol normally suppresses antidiuretic hormone (ADH); a lack of cortisol leads to elevated ADH and subsequent free water retention. Crucially, the serum potassium is normal. In ACTH deficiency (secondary adrenal insufficiency), aldosterone production is preserved because it is primarily regulated by the renin-angiotensin-aldosterone system (RAAS) and serum potassium levels, not ACTH. This intact mineralocorticoid function prevents hyperkalemia, distinguishing hypopituitarism from primary adrenal insufficiency.

Step-by-Step Solution

1
Identify signs of severe metabolic derangement.
The infant presents with severe hypoglycemia (34 mg/dL) and hyponatremia (132 mEq/L), indicating a deficiency in counter-regulatory hormones such as cortisol and/or growth hormone.
Recognizing these metabolic abnormalities narrows the differential diagnosis to adrenal or pituitary etiologies.
2
Analyze the serum potassium level.
The serum potassium is perfectly normal (4.2 mEq/L).
A normal potassium level suggests intact aldosterone secretion. This rules out primary adrenal insufficiency (such as classic congenital adrenal hyperplasia) and points toward secondary (pituitary) adrenal insufficiency, where the renin-angiotensin-aldosterone system remains functional.
3
Correlate metabolic findings with the genitourinary examination.
The presence of a micropenis and bilateral nonpalpable testes indicates a deficiency in fetal testosterone during the second and third trimesters, a process driven by fetal pituitary LH.
Combining secondary adrenal insufficiency with LH/FSH deficiency (and likely TSH deficiency causing the prolonged jaundice) firmly establishes the diagnosis of panhypopituitarism.

Key Concept

Neonatal presentation of panhypopituitarism
Rate this question

Topics

Pediatric Endocrine Disorders

More questions from this topic