Approach to hyponatremia (pediatrics) Quiz: Ace Your Exams

A 5-year-old girl is brought to the emergency department for headaches and confusion. Her parents report progressive periorbital swelling and abdominal and ankle swelling for the past 10 days. The patient had a sore throat two months ago, but no other illnesses or medications. There is no known family history of kidney disease. Temperature is 37°C (98.6°F), pulse is 100/min, respirations are 25/min, and blood pressure is 130/70 mmHg. Weight is 23 kg, but it was 18 kg two weeks ago. On examination, she is oriented to person only. She has puffy lower eyelids and pitting edema in bilateral lower limbs. Capillary refill is 3 seconds with moist mucous membranes. Heart rate is regular with no murmurs or gallops. The patient has difficulty breathing when lying flat but has clear lungs bilaterally. Abdomen is soft and non-tender without hepatomegaly. Initial laboratory results are shown below. Which of the following is the most likely cause of hyponatremia in this patient?

Laboratory value	Result
Hemoglobin	12.5 g/dL
Leukocyte count	6500 /mm³
Platelets	370,000/mm³
Blood urea nitrogen	10 mg/dL
Sodium	130 mEq/L
Potassium	3.3 mEq/L
Creatinine	0.4 mg/dL
Serum osmolality	240 mOsm/kg
Serum albumin	2.5 g/dL
Urine sodium	8 mmol/L
Urine protein	+4
Urine glucose	Negative