Bartter Syndrome Suggested by Polyuria and Nocturia

Diagnosis

The diagnosis of Bartter syndrome can be confirmed by a combination of clinical features and laboratory findings. The mostconsistent finding is persistent hypokalemia. Potassium levels often range from 2.5 to 3.0 mEq/L; even with treatment, potassium levels remain at the lower end of the normal range. In addition, urinary potassium and chloride levels are elevated, with chloride levels usually exceeding 10 mEq/L. Metabolic alkalosis also is present.

Patients who have Bartter syndrome are normotensive despite elevated renin and aldosterone levels. Less consistent findings include hypomagnesemia, hyperuricemia, and hypercalciuria. Increased urinary prostaglandin secretion also may be noted and is thought to result from a relative volume contraction that is related to the defective chloride reabsorption. A relative resistance to the pressor effects of norepinephrine and angiotensin II and an impaired ability to concentrate urine also have been described in patients who have Bartter syndrome.

The differential diagnosis of Bartter syndrome includes both inborn and acquired disorders. Inborn etiologies include several syndromes. Patients who have Gitelman syndrome present with primary renal tubular metabolic alkalosis; however, they also have magnesium deficiency and hypocalciuria (in contrast to the hypercalciuria sometimes found in patients who have Bartter syndrome). These children often suffer tetanic episodes that may occur during febrile seizures, and they can manifest growth failure, usually after the age of 6 years. In addition, the chemistry pattern in patients who have Gitelman syndrome may resemble that of patients using thiazide diuretics, while those who have Bartter syndrome often demonstrate patterns consistent with the use of loop diuretics. One aspect of Liddle syndrome is hypokalemic metabolic alkalosis, but the overall clinical picture resembles primary hyperaldosteronism with hypertension. Renal tubular acidosis also is associated with hypokalemia, but this disorder causes metabolic acidosis. Finally, metabolic alkalosis may occur in pyloric stenosis and cystic fibrosis.

Acquired conditions to consider are chronic diarrhea, chronic diuretic therapy, and diuretic abuse, including antenatal abuse by mothers. An interesting cause of hypokalemic metabolic alkalosis was noted in 1979 in infants receiving soy formulas deficient in chloride. This pattern also may be seen in situations of starvation involving deficient chloride intake. It is relevant to note that when chloride intake is limited to less than 10 mEq/day, the chloride loss stops in those who have exogenous disorders, whereas patients who have Bartter syndrome will continue to have chloride wasting, even with chloride restriction, because of their renal defect.

Treatment

Treatment is aimed at balancing the renal potassium loss through oral potassium supplementation with potassium as the chloride salt at dosages ranging from 1 to 3 mEq/kg per day, up to 200 mEq per day, together with the use of potassium-sparing diuretics, such as spironolactone at 15 mg/kg per day, triamterene at 5 to 10 mg/kg per day, or amiloride. Therapy is intended to keep the serum potassium level above 3.5 mEq/L. Prostaglandin inhibitors, such as indomethacin at 5 mg/kg per day or ibuprofen at 30 mg/kg per day, also are used and are thought to increase height and weight and to reverse growth failure. Treatment may improve cognitive functioning, but most patients continue to have some impairment; those at greatest risk are ones who develop symptoms in early infancy and require several hospitalizations during infancy and early childhood. Complications of Bartter syndrome include an increased risk of recurrent urinary tract infections, chronic renal insufficiency, nephrocalcinosis, gout, interstitial nephritis, and subacute necrotizing or Leigh encephalopathy.

Errol C. Baptist, MD, Michelle M. Bittle, University of Illinois College of Medicine, Rockford, IL

Pediatrics in Review Volume 18 Number 1 January 1997 Copyright 1997 American Academy of Pediatrics

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