Night-time polyuria and urine hypo-osmolality in enuretics identified by nocturnal sequential urine sampling - Do they represent a subset of relativeADH-deficient subjects?

Early morning urine osmolality was tested in two urinary specimens, one tak en immediately upon awakening and the other approximately 30 min thereafter , in 52 enuretic and 15 non-enuretic children. In a follow-up study, using the same study population, urine osmolality and volume were measured sequen tially at 3-h intervals at 19.00, 22.00, 01.00, 04.00 and 07.00 h. Thereaft er, all enuretics were treated by intranasal DDAVP for a 6-month period. Th ere were no differences in urinary osmolality between enuretic and non-enur etic children when comparing the two early morning specimens. Nor were ther e any differences between groups in urine osmolalities at 19.00, 01.00 and 07.00 h. In contrast, at 04.00 h, urine osmolality was significantly lower in 17 of 52 enuretics [designated as ADH-negative (ADH-)] compared to the r emaining enuretics [designated as ADH-positive (ADH+)] and non-enuretic chi ldren (610 +/- 251 vs 995 +/- 195 and 1089 +/- 195 mosmol/kg H2O, respectiv ely, p < 0.05). This decreased osmolality was paralleled by an increase in urine production during the time period 01.00-04.00 (83 +/- 24 vs 52 +/- 18 and 45 +/- 22 mi, respectively, p < 0.05). At the end of the 6-month perio d of DDAVP treatment, the percentage response was similar between the ADH- and ADH+ enuretics (79% vs 75%). However, the time taken to achieve a respo nse was quicker in the ADH- subjects. These data suggest the existence of a subgroup of enuretics whose underlying pathophysiology is the development of nocturnal polyuria probably due to a relative night-time ADH deficiency. Nocturnal sequential monitoring of urinary osmolality, as described above, allows identification of this subgroup.