"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.
To learn more about bedwetting and ways to cope, visit the Nemours Foundation KidsHealth.
SOURCES: Jeffrey Stock, M.D., chief, division of pediatric urolog
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