PEDIATRIC UROLOGY

Bladder Reservoir Function in Children with Monosymptomatic Nocturnal Enuresis and Healthy Controls
Hagstroem S, Kamperis K, Rittig S, Djurhuus JC
Clinical Institute, University of Aarhus and Department of Pediatrics, Skejby University Hospital, Denmark
J Urol. 2006;176:759-63

• Purpose: We investigated bladder reservoir function in children with monosymptomatic nocturnal enuresis and in healthy controls.
• Materials and Methods: A total of 18 children with monosymptomatic nocturnal enuresis and 119 controls who were 7 to 13 years old were recruited. Children completed frequency volume charts and measurements of nocturnal urine production. Mean diuresis in the period preceding each voiding was calculated. Those with enuresis were grouped according to bladder capacity and hospitalized for 4 nights, including a baseline night and 3 with an oral water load. Enuresis volumes and post-void residual volume were estimated, allowing the calculation of bladder volume at the time of enuresis.
• Results: Nine children with monosymptomatic nocturnal enuresis were characterized as having normal bladder capacity and 9 had decreased bladder capacity. We found large intra-individual variability in daytime voided volume in all 3 groups of participants. Children with enuresis and small bladder capacity generally voided with volumes close to maximal voided volume. A total of 93 enuresis episodes were recorded. Large intra-individual variability was seen in bladder volume at enuresis and it was lower than maximal voided volume in more than 50% of episodes. Variability in bladder volume at enuresis was greatest in the patient group with decreased bladder capacity. We found a significant correlation between diuresis and bladder capacity in all groups during the day and night.
• Conclusions: There is a great intra-individual diurnal variability in voided volume in children with enuresis and in healthy children. Enuresis seems to occur at bladder volumes that are smaller and larger than the maximal voided volume obtained from voiding charts.
  
  
• Editorial Comment
  The authors attempted to measure bladder size in children using voiding diaries and, in enuretic children, observed voiding overnight in hospital, including after water loading. They found that about half of children with enuresis had smaller than expected functional bladder capacity. However, there was a large intra-individual variability, both in normal controls and children with enuresis. Similarly, looking at nocturnal enuretic episodes in particular, there was wide variation and at least 50% of episodes occurred at volumes less than the maximal voided volume during the day. Finally, water loading appeared to increase functional bladder size.
  These findings are of considerable interest. First, the finding of smaller then expected bladder capacity suggests that some of the children may well benefit from anticholinergic therapy. Of course, this has been recognized in the past and the children who do respond are limited. What is interesting, yet disconcerting is the wide variation. Though not particularly surprising, as many social and behavioral factors can influence voiding function, this calls into question the usefulness of short-term voiding diaries. These diaries are the initial non-invasive assessment in most children with voiding problems, yet are clearly highly flawed as a tool to estimate bladder capacity. Also concerning is the finding that for control children the largest voided volume was usually the first void in the AM. In children with nocturnal enuresis, in whom the diary would be most useful, this measurement will clearly not be comparable (as the child will have voided during the night). This again limits the usefulness of the voiding diary. An interesting finding that might have therapeutic benefit is the determination that water loading could, over a few days, lead to larger voided volumes. If so, could morning water loading be of benefit to nocturnal enuresis? Further studies are needed.

Dr. Barry A. Kogan
Chief and Professor of Urology and Pediatrics
Albany Medical College
Albany, New York, USA