Bartter Syndrome Suggested by Polyuria and Nocturia

Presentation

A 6-year-old boy who is developmentally delayed is brought to your office because he has been experiencing polydipsia, nocturia, and polyuria for several months. He is 3 to 4 years delayed in language, motor, and social skills. Physical examination reveals a healthy-looking child whose height and weight are between the 5th and 10th percentiles. All vital signs are normal, and no abnormalities are found on complete physical examination.

Laboratory evaluation includes a normal complete blood count and differential leukocyte count. His serum sodium is 136 mEq/L, potassium is 2.8 mEq/L, chloride is 90 mEq/L, blood urea nitrogen is 12 mg/dL, and serum creatinine is 0.4 mg/dL. Radiographs of his hands and wrists reveal a normal bone age. Arterial blood gas levels reveal a pH of 7.62 (normal, 7.35 to 7.45), PCO2 of 32 torr (normal, 36 to 46 torr), base excess of +11.1 (normal, +/- 2.3), and total CO2 of 34.2 mmol/L (normal, 23 to 27 mmol/L). His urine has a pH of 8.0 and specific gravity of 1.010. No glucose, protein, blood, or ketones are present. The available data suggest a specific diagnosis, which is confirmed by additional tests.

Discussion

The presence of hypokalemia and metabolic alkalosis in a patient who has severe developmental delay, polyuria, and nocturia strongly suggests Bartter syndrome. The diagnosis was supported in this child by finding elevated plasma levels of renin, prostaglandin E2, and aldosterone, as well as high urinary levels of potassium and chloride.

In 1962, Bartter described a syndrome of renal potassium wasting characterized by hypokalemia, metabolic alkalosis, and normal blood pressure (despite hyperreninemia and hyperaldosteronism). The pathogenesis of the syndrome derives from a primary defect in chloride reabsorption in the ascending limb of the loop of Henle. This abnormality leads to a reduced medullary hypertonicity and contributes to the concentrating defect found in this syndrome. Excess sodium chloride is delivered to the distal tubule, resulting in a potassium loss in the sodium exchange, which secondarily causes hypokalemic metabolic alkalosis. The alkalotic state stimulates prostaglandin synthesis, resulting in an increased renin release and an increased aldosterone synthesis that exacerbates the renal potassium loss.

Classically, the initial presentation of patients who have Bartter syndrome includes growth failure, poly-uria, polydipsia, nocturia, and dehydration. Among the other signs and symptoms are generalized weakness, muscle cramps, and neuromuscular irritability, which most commonly are consequences of hypo- kalemia. Growth failure and mental retardation usually accompany the syndrome in children who present with the metabolic abnormalities before the age of 10 years, and the adolescent growth spurt is delayed. These patients are in a state of malnutrition during childhood, with poor muscle mass, low serum potassium, and low serum magnesium. Most patients, however, eventually attain normal stature. The spectrum of intellectual capability varies from normal intelligence to severe retardation. Most patients exhibit some deficit throughout their lives.

There is a form of Bartter syndrome that affects adults. Unlike children, older patients do not show delayed physical or mental maturation; rather, they present with weakness, muscle cramps, polyuria, and abdominal pain.

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