What is the role of small functional bladder capacity (FBC) in the etiology of enuresis?

Updated: Mar 26, 2020
  • Author: Wm Lane M Robson, MA, MD, FRCP, FRCP(Glasg); Chief Editor: Marc Cendron, MD  more...
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Small functional bladder capacity (FBC) is now known to play a role in the pathogenesis of enuresis. For some time, it was considered a less likely explanation for enuresis in children without daytime symptoms, but studies confirmed that children without daytime symptoms may have a low nocturnal bladder capacity and that this is a very common factor in enuresis.

In a study by Mattsson and Lindstrom, FBC was positively correlated with nighttime urine output. [10] It has been theorized that children with enuresis may maintain a smaller nocturnal bladder volume and that this situation may condition the detrusor muscle to contract at a lower volume. According to this theory, the low nocturnal bladder capacity is a consequence of enuresis rather than a cause.

Bloom et al suggested a problem with the external urethral sphincter as a possible cause of low nocturnal bladder capacity, [11] noting that the control of voiding rests at the external urethral sphincter, where constant activity is present as a guarding reflex to preserve continence. They speculated that the activity of the external urethral sphincter might fall below a critical level during sleep and thereby trigger a detrusor contraction.

Chronic constipation may also lead to reduced bladder capacity due to accumulation of stool in the distal colon.

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