WEDNESDAY, May 28 (HealthDay News) -- Much like the boy who cried wolf, a bladder that constantly sends signals to arouse the brain may end up being ignored in its time of greatest need.

That's the theory of Hong Kong researchers who compared the amount of arousal in the cortical area of the brain that occurs during sleep in children with a history of bedwetting to a control group of children. They found that children with a history of night-time accidents, also known as enuresis, had almost twice the number of cortical arousals compared to children who didn't wet the bed.

"We found that children with enuresis have more light sleep associated with frequent cortical arousals, but an inability to awaken completely. We speculate that the transition from light sleep to complete awakening, as elicited by the arousal center, may be paradoxically suppressed by long-term overstimulation by signals from the bladder," the study authors wrote.

The findings are published as a letter to the editor in the May 29 issue of the New England Journal of Medicine.

In the United States, bedwetting is a problem for as many as 5 million children, according to the National Institutes of Health. While there's no set age that children grow out of bedwetting, each year as children grow older, fewer and fewer experience enuresis.

Experts haven't yet pinpointed the exact cause or causes of bedwetting, but they do know that certain factors contribute to the problem.

"We know there's a genetic component. If both parents have a history of bedwetting, there's at least a 70 percent chance that the child will," said Dr. Jeffrey Stock, chief of the division of pediatric urology at Mount Sinai Medical Center in New York City.

Stock said there's also a connection between sleep cycles and bedwetting, and that the reflex that suppresses urine discharge is suppressed at night in children who wet the bed.

"The bladder in an infant works as a reflex organ and automatically contracts. But, we learn to suppress that reflex," explained Stock, who added that children who wet the bed at night usually control the reflex during the day, but when they go to sleep, they revert to the infant sleep pattern and don't suppress the bladder's reflex action.

Another possible factor is a hormone called anti-diuretic hormone that keeps the body from excreting fluids.

"Children who wet the bed don't make enough anti-diuretic hormone," said Dr. Francis Schneck, clinical director of pediatric urology at Children's Hospital of Pittsburgh. But, he noted that when kids are given a medication that replaces this hormone, only about six in 10 are helped, suggesting the problem has several components.

The new study compared 35 children with enuresis to 21 "control" children with no history of bedwetting. The median age of the children with enuresis was 9.5, while the median age of the controls was 10.3 years old.

The researchers found that children who wet the bed experienced more cortical arousals than children in the control group did. They also found that cortical arousals were associated with bladder contractions, suggesting a "bladder-brain dialogue," according to the authors. But, despite the cortical arousals and the bladder-brain dialogue, the children who wet the bed seemed to have an inability to awaken completely.

"This study gives us something to consider, but I'm not sure it will have a huge effect on the management of enuresis," Schneck said.

More information

To learn more about bedwetting and ways to cope, visit the Nemours Foundation KidsHealth.

SOURCES: Jeffrey Stock, M.D., chief, division of pediatric urology, Mount Sinai Medical Center, New York City; Francis Schneck, M.D., clinical director, pediatric urology, Children's Hospital of Pittsburgh; May 29, 2008, New England Journal of Medicine

Copyright © 2008 ScoutNews, LLC. All rights reserved.