A 6-month-old infant is admitted with severe pneumonia and is noted to have serum sodium of 124 mEq/L with urine sodium >40 mEq/L and urine osmolality >100 mOsm/kg. The most likely mechanism of hyponatremia in this child is:
- A Syndrome of inappropriate ADH secretion (SIADH) — common with CNS and pulmonary infections ✓
- B Cerebral salt wasting
- C Iatrogenic hypotonic IV fluid administration
- D Adrenal insufficiency
Correct answer: A. Syndrome of inappropriate ADH secretion (SIADH) — common with CNS and pulmonary infections
Explanation
SIADH is the most common cause of euvolemic hyponatremia in children with pneumonia or CNS infection. Diagnostic criteria include low serum Na, concentrated urine (osmolality >100), elevated urine Na (>40 mEq/L), and clinical euvolemia. ADH is released non-osmotically due to pulmonary or CNS disease. Cerebral salt wasting also shows urinary Na loss but with clinical hypovolemia (distinguishing feature). Treatment is fluid restriction, not sodium supplementation, unless sodium <120 with symptoms.
Reference: Ghai Essential Pediatrics, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.