(HealthDay)—Children who suffer from epilepsy or fever-related seizures may face a higher risk of also having attention-deficit/hyperactivity disorder (ADHD), new Danish research suggests.
The findings echo those of some previous research. But, U.S. experts said the new study is notable because of the large number of study participants—nearly 1 million—and the length of follow-up, which was up to 22 years.
The study looked at children born in Denmark from 1990 through 2007, tracking them until 2012. The investigators found those with epilepsy seemed to have nearly three times the risk of developing ADHD compared to children without epilepsy. And children who had fever-related seizures appeared to have an almost 30 percent increased risk of ADHD.
Children with both epilepsy and fever-related seizures had a risk of ADHD more than three times higher than those without a history of either condition, the findings suggested.
The researchers only found an association, and couldn't prove cause and effect. Even so, the links held up even after the researchers took into account other factors that might have affected risk, such as birth weight and family history of neurodevelopmental disorders or epilepsy.
"The link between these conditions is not surprising," said Dr. Josiane LaJoie, a pediatric neurologist at NYU Langone Comprehensive Medical Center in New York City. "All have their root within the central nervous system."
Another pediatric expert agreed.
"Overall, it strengthens the finding which people have found before," said Dr. Sayed Naqvi, a pediatric neurologist and epileptologist at Nicklaus Children's Hospital in Miami.
Naqvi said he has seen the link between epilepsy and ADHD in his own patients, but not one between fever-related seizures and ADHD.
ADHD is a common neurodevelopmental condition, marked by inattention, inability to focus and impulsivity. Fever-related seizures usually involve a fever of 102 degrees Fahrenheit or above. Epilepsy is a brain disorder that causes seizures.
It isn't known why the conditions seem to be linked. However, the researchers speculated that common genetic risk factors might help explain the connection, among other possibilities. The three conditions share some other risk factors, including low birth weight and family history.
The study has limitations, Naqvi said, and the researchers addressed them in the report. For instance, no information was available on the medications given to treat epilepsy, so the drugs could have affected the risk of developing ADHD, the researchers noted.
The take-home message for doctors, the Danish researchers said, is to identify ADHD early so treatment can be initiated before symptoms become problematic.
Parents of children with either epilepsy or a history of fever-related seizures should be on the lookout for possible ADHD symptoms, said Naqvi. One of the first warnings, if the child has started school, is a decline in school performance, he said. "That could be a red flag," he said.
And, LaJoie added, "It is vital that when caring for a child with epilepsy, some of the medical visit involves attention to academic achievement and psychosocial functioning."
The study was published online July 13 in the journal Pediatrics.
Explore further: One in five adults with epilepsy also has ADHD symptoms
To learn more about epilepsy, visit the Epilepsy Foundation.