Index of Suspicion

Case 1 Presentation

A 15-year-old boy comes to the emergency department because of acute chest pain, weakness, and dizziness, followed by a syncopal attack. He has had no fever and denies taking medications or illicit substances. He reports weight loss of 11.25 kg (25 lb) over the past 6 months, but has had a good appetite and normal bowel habits. There is no family history of serious medical problems.

Physical examination reveals a slender boy who is 170 cm (68 in) tall, weighs 47.5 kg (105.6 lb), is afebrile, and is in no distress. His blood pressure is 109/56 mm Hg seated and 101/51 mm Hg standing. His resting pulse rate is 65 beats/min in a regular rhythm. Findings on physical examination, including funduscopic evaluation, are otherwise normal, and there are no signs of dehydration.

Laboratory tests reveal: serum sodium, 135 mmol/L (135 mEq/L); potassium, 2.5 mmol/L (2.5 mEq/L); chloride, 81 mmol/L (81 mEq/L); and bicarbonate (HCO₃), 34 mmol/L (34 mEq/L). Venous blood gas analysis reveals: pH, 7.51; Pco₂, 45 mm Hg; HCO₃, 33 mmol/L; and base excess, +8.0. The electrocardiogram shows first-degree atrioventricular block with a prolonged QT interval. A complete blood count; liver function tests; and measurements of serum calcium, phosphorus, blood urea nitrogen, creatinine, and cardiac enzymes all yield normal results. The urine is alkaline (pH, 9), but otherwise normal. A 24-hour urine collection indicates excretion of chloride, 5 mEq; sodium, 20 mEq; and potassium, 4 mEq.

He is given intravenous fluids supplemented with potassium chloride. An electrocardiogram 24 hours later reveals normal sinus rhythm and a normal QT interval. After 48 hours of therapy, his electrolyte concentrations have normalized. Additional history obtained from the boy’s mother reveals the cause of his problem.

Case 2 Presentation

A 2-year-old boy is admitted to the hospital because of “yellow …