Circadian rhythm of urinary water and sodium excretion in children with MNE and NMNE enuresis

Background Nocturnal enuresis (NE) is caused by a mismatch of nocturnal urine production and functional bladder capacity. The International Children’s Continence Society defines nocturnal polyuria (NP) as nocturnal diuresis (ND) exceeding the Expected Bladder Capacity (EBC) by 130%. NP is well documented as pathogenetic mechanism in monosymptomatic, but little is known of its incidence/characteristics in non-monosymptomatic enuresis. NP is attributed to abnormal circadian rhythm of vasopressin (AVP). However, 40-60% of patients treated with desmopressin, an AVP agonist, show insufficient response, suggesting other factors like nutrition and circadian rhythm of other renal functions may be involved. Methods We aimed to study the kidney circadian rhythm on water and solute excretion in fractionated urine samples over 24h (4 day and 4 night samples); we analyzed retrospectively data from 402 enuretic. The children were divided into 3 subgroups a) low-normal ND ( 130% EBC, n=91). Results Increased diuresis rate and free water clearance overnight is present in the NP and the high-normal ND group. Both groups demonstrate an abnormal circadian rhythm of diuresis (p=0,001) and of osmolary excretion (p<0,001), predominantly in the two first nighttime samples. Children with NP produced more urine (p<0,003) and excreted more osmols (p<0,001) overnight but also during the daytime and in a 24h-period. Conclusion Where the clinical indication for desmopressin is often restricted to children with NP (>130%EBC), our data suggest that: • NP is better defined as ND>100% EBC; this population might be equally desmopressin responsive • pathogenesis is more complex than an abnormal AVP circadian rhythm; in 60% of patients abnormalities of other renal circadian rhythms and/or increased nutritional intake might be involved • NP is the highest and osmolality the lowest in the early night collections; treatment should target fast rather than long-term action