Pathophysiology and treatment of enuresis in adults

Monosymptomatic nocturnal enuresis (MNE) in children is partly the result of inadequate reduction in the rate of urine output at night. This nocturnal polyuria is due to the lack of a rise in the anti-diuretic hormone, arginine vasopressin (AVP), and can be reduced or eliminated by treatment with desmopressin at bedtime. Since there is a 1% incidence of MNE among adults, this study investigated the circadian pattern of solute and water balance in nine young adult enuretics before and during desmopressin therapy and compared the results with nine-age- and sex-matched, healthy controls. Before treatment, enuretics and controls had similar total fluid intake, urine output, urine osmolality, plasma osmolality, plasma total protein, mean arterial pressure and plasma AVP. The circadian pattern of fluid intake was also normal in enuretics. This abnormality could not be attributed to a deficiency of plasma AVP or an increase in solute excretion, since both variables were similar to controls. Rather, their nocturnal polyuria appeared to be due to a marked nocturnal reduction in renal sensitivity to the antidiuretic effect of vasopressin. In seven enuretics, restudied during treatment with desmopressin (10-30 micrograms o.d.), circadian urine output was normal and enuresis was absent. These results indicate that: (i) The circadian pattern of urine output in healthy adults is largely due to a nocturnal decrease in solute excretion rather than a rise in plasma AVP; (ii) The subset of adults with persistent MNE also have nocturnal polyuria as a result of insensitivity to the antidiuretic action of AVP; (iii) These defects can be corrected by treatment with desmopressin.