Hypercalciuria might also be involved in the pathogenesis of enuresis associated with nocturnal polyuria. Raes et al investigated if modifications in renal function are involved in nocturnal enuresis. They assessed circadian variation in natriuresis and tubular sodium handling in polyuric hypercalciuric children.

They had a total of 10 children with proved hypercalciuria and nocturnal polyuria and 10 age matched controls. A 24-hour urine collection was performed in 8 sampling periods for measurement of urinary sodium excretion. Segmental tubular sodium transport was investigated during a daytime oral water load test and calculated according to standardized clearance methodology. The children with enuresis showed a marked increase in the fractional excretion of sodium during the night (0.93%?± 0.36%), while daytime sodium excretion was decreased (0.84% ± 0.23%). Analysis of segmental tubular sodium transport revealed decreased delivery of sodium to distal tubule (CH2O + CNa = 10.7 ml/100 ml glomerular filtration rate). This indicated that not only was there increased proximal tubular sodium reabsorption but also stimulation of distal sodium reabsorption. It was shown by increased fractional distal sodium reabsorption (92.9% ± 2.2%, controls 90.5% ± 2.9%). Increased distal reabsorption was associated with increased fractional potassium excretion (17.5% ± 2.7%, controls 13.6% ± 6.4%), indicating increased distal tubular sodium/potassium exchange.

The group concluded that there was no intrinsic defect in renal tubular sodium transport, but during the day increased sodium reabsorption in proximal and distal tubules was observed. This suggested that extrarenal factors might be involved in altered circadian variation in solute and water excretion by the kidney.

Raes A, Dehoorne J, Hoebeke P, Van Laecke E, Donckerwolcke R, Vande Walle J

Journal of Urology 176(3): 1147-1151, September 2006.

Written by Pasquale Casale, MD, a Contributing Editor with UroToday.

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