Clinical Scenario:
A 9-year-old boy is evaluated for recurrent episodes of muscle weakness and fatigue over the past year. His parents also report excessive thirst and passage of large volumes of urine. His growth has been below the expected percentile for age. On examination, blood pressure is 90/60 mmHg. Laboratory investigations show metabolic alkalosis with normal serum sodium and renal potassium wasting. Urinary calcium excretion is increased.
What is the most likely diagnosis?
A. Bartter syndrome
B. Gitelman syndrome
C. Liddle syndrome
D. Primary hyperaldosteronism
E. Renal tubular acidosis
Correct answer & Explanation:
Correct Answer: A. Bartter syndrome
Explanation
Bartter syndrome is an inherited defect of the Na-K-2Cl cotransporter in the thick ascending limb of the loop of Henle, producing a clinical picture similar to chronic loop diuretic use.
Typical features include:
- Chronic hypokalemia
- Metabolic alkalosis
- Normal or low blood pressure
- Polyuria and polydipsia
- Growth failure
- Renal potassium wasting
- Hypercalciuria (important distinguishing feature)
Why the other options are incorrect
A. Bartter syndrome
Correct. The combination of hypokalemia, metabolic alkalosis, normal/low blood pressure, polyuria, growth failure, and hypercalciuria is classic.
B. Gitelman syndrome
Usually presents later in childhood or adolescence with hypokalemia and metabolic alkalosis but is characterized by hypocalciuria and hypomagnesemia, not hypercalciuria.
C. Liddle syndrome
Causes hypertension with hypokalemic metabolic alkalosis due to increased ENaC activity. This child is hypotensive.
D. Primary hyperaldosteronism
Typically causes hypertension together with hypokalemia and metabolic alkalosis.
E. Renal tubular acidosis
Usually causes metabolic acidosis, not metabolic alkalosis.
Learning Point
A useful board-style distinction:
| Feature | Bartter Syndrome | Gitelman Syndrome |
|---|---|---|
| Blood pressure | Normal/Low | Normal/Low |
| Acid-base status | Metabolic alkalosis | Metabolic alkalosis |
| Urinary calcium | High | Low |
| Serum magnesium | Usually normal | Low |
| Typical age | Infancy/Childhood | Late childhood/Adolescence |
