To determine if urine osmolality parameters can predict whether children with primary monosymptomatic nocturnal enuresis will respond to desmopressin, we conducted a prospective, double-blind, placebo-controlled study in 96 children 8 to 14 years old. Following a 2-week baseline screening interval patients with at least 6 of 14 wet nights were randomized to double-blind regimens of desmopressin or placebo. Urine specimens for osmolality were collected at 6 p.m. and 6 a.m. on 3 consecutive days during the baseline and the 2, 14-day treatment periods. A significantly greater proportion of desmopressin treated children had an excellent (2 or fewer wet nights in 14 days) or good (greater than 50 percent reduction in wet nights) response compared with placebo treated children (p = 0.004 and p = 0.002 for treatment periods 1 and 2, respectively). Children treated with desmopressin reported a significantly lower number of wet nights than placebo treated children during both treatment periods (p = 0.0258 and p = 0.0136, respectively). Children treated with desmopressin had a significantly higher 6 a.m. urine osmolality during both treatment periods and a higher 6 a.m.-to-6 p.m. osmolality ratio (p = 0.004) in the first treatment period compared with the placebo group. Within the desmopressin treatment group clinical responders had a higher 6 a.m. urine osmolality and 6 a.m.-to-6 p.m. urine osmolality ratio than nonresponders during both treatment periods but these differences did not achieve statistical significance. In conclusion, treatment with desmopressin is associated with a significant decrease in the number of wet nights, and a significant increase in nocturnal urine osmolality and nocturnal/diurnal urine osmolality ratios. However, clinical response was not predictable based on baseline or treatment osmolality parameters.
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