Nocturnal polyuria and nocturnal arginine vasopressin (AVP): a key factor in the pathophysiology of monosymptomatic nocturnal enuresis.

AIMS To identify the relationship between nocturnal AVP deficiency, nocturnal polyuria (NP), and low urinary osmolality in children suffering of primary monosymptomatic nocturnal enuresis (NE). PATIENTS AND METHODS The study included 50 children (28 males and 22 females) with primary monosymptomatic NE and 30 non enuretic children of the same age group (controls). Night samples of blood and urine were obtained for AVP, blood osmolality, and urine osmolality. In addition, volume frequency charts, arousal threshold, and urodynamics were performed for these children. RESULTS Twenty eight (56%) of the enuretic children were considered to have NP. Mean AVP level was 44.80 +/- 8.19 and 32.49 +/- 18.25 pg/ml while mean urine osmolality was 865.07 +/- 158.66 mOsm/kg and 700.06 +/- 84.42 mOsm/kg in controls and enuretic group respectively. These differences were highly significant. No significant difference was found between the controls and enuretics without NP. On the other hand, nocturnal AVP and urine osmolality were significantly lower in enuretics with NP when compared to both controls and enuretics without NP. Blood osmolality did not reach statistically significant difference between subgroups. Arousal threshold was significantly higher in enuretic children irrespective to NP. The timing for NE episodes were predominantly late in the night in NE children without NP while patients suffering of NE with NP typically experienced multiple incidents each night. CONCLUSION We have shown that low nocturnal AVP and urine osmolality may play a role in the pathophysiology of enuretics with NP. This abnormality doesn't occur as an isolated disease as these children suffer from arousal defect as well.