Bladder capacity and renal concentrating ability in enuresis: pathogenic implications

We compared bladder volume and renal concentrating capacity in dry children and 2 distinct groups of children with enuresis to hypothesize about the pathogenesis of various types of enuresis.

A total of 55 dry children and 100 with enuresis underwent an overnight thirst provocation test to assess renal concentrating capacity and completed a 2-day voiding chart to assess functional bladder capacity. The enuretic children were subdivided into 27 desmopressin responders and 73 desmopressin nonresponders before study inclusion.

The desmopressin responder group had lower average renal concentrating capacity +/-1 standard deviation than dry children and desmopressin responders (856 +/- 158 mOsm./kg. versus 939 +/- 147 and 962 +/- 151, respectively, p <0.05). Analogously average daytime urine production in the desmopressin responder group was greater than in dry children and desmopressin responders (22.2 +/- 10.2 ml./kg. body weight versus 15.4 +/- 7.3 and 15.3 +/- 7.2, respectively, p <0.01). Average functional bladder capacity expected for age was less in desmopressin nonresponders than in dry children and responders (52.2% +/- 19.9% versus 79.2% +/- 30.4% and 69.5% +/- 25.7%, respectively, p <0.001).

Desmopressin responders produced larger amounts of less concentrated urine than the other children, while desmopressin nonresponders had smaller bladder capacity than the other groups. These results support the idea that enuretic children who respond favorably to desmopressin treatment have polyuria, whereas children with therapy resistant enuresis have detrusor hyperactivity.