Bladder capacity and renal concentrating ability in enuresis: Pathogenic implications

Purpose: We compared bladder volume and renal concentrating capacity in dry children and 2 distinct groups of children with enuresis to hypothesize ab out the pathogenesis of various types of enuresis. Materials and Methods: A total of 55 dry children and 100 with enuresis und erwent an overnight thirst provocation test to assess renal concentrating c apacity and completed a X-day voiding chart to assess functional bladder ca pacity. The enuretic children were subdivided into 27 desmopressin responde rs and 73 desmopressin nonresponders before study inclusion. Results: The desmopressin responder group had lower average renal concentra ting capacity +/-1 standard deviation than dry children and desmopressin re sponders (856 +/- 158 mOsm./kg. versus 939 +/- 147 and 962 +/- 151, respect ively, p <0.05). Analogously average daytime urine production in the desmop ressin responder group was greater than in dry children and desmopressin re sponders (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 re sponders (52.2% +/- 19.9% versus 79.2% +/- 30.4% and 69.5% +/- 25.7%, respe ctively, p <0.001). Conclusions: Desmopressin responders produced larger amounts of less concen trated urine than the other children, while desmopressin nonresponders had smaller bladder capacity than the other groups. These results support the i dea that enuretic children who respond favorably to desmopressin treatment have polyuria, whereas children with therapy resistant enuresis have detrus or hyperactivity.