Researchers say it can take up to a decade for attention deficit hyperactivity disorder symptoms to show up in children after they have a serious head injury.

Children who have had a serious head injury are more likely to develop attention deficit hyperactivity disorder (ADHD) — but new research suggests that symptoms may not develop for up to a decade later.

Traumatic brain injury (TBI) is a frequent cause for hospitalization in young children and teenagers. It’s associated with developing mental conditions, including secondary ADHD, a form of ADHD that develops following an injury.

Approximately 1 in 5 children who’ve had TBI will also develop ADHD, but it usually manifests within a few years.

However, a study published today in JAMA Pediatrics says that it may take significantly longer in some cases.

“Children with a history of TBI, even those with less severe injuries, have an increased risk for the development of new-onset attention problems, potentially many years after injury,” Megan Narad, PhD, lead author and postdoctoral fellow at Cincinnati Children’s Hospital Medical Center, told Healthline.

“While previous studies suggest kids with a history of TBI are at risk for developing attention problems, they only followed kids two to three years after injury. Our study is unique in that we followed children 7 to 10 years after their injury,” she said.

Narad’s research looked at 187 children with no prior history of ADHD who were hospitalized due to either TBI or other accidents, including fractures and broken bones.

Study participants were between the ages of 3 and 7 at the time of hospitalization. Their parents completed behavioral assessments at the time of injury and every six months for a period afterward.

Of the 187 children, 48 eventually met the definition for secondary ADHD, roughly 25 percent of the group. The risk for developing the disorder was, in cases of severe TBI, four times higher than the rest of the children.

But, Narad points out, even children with less severe head injuries were also at risk of developing symptoms many years later.

“I think this is important to point out, as these kids are often perceived as being recovered from their injury, when in fact they may be at greater risk for SADHD,” she said.

Narad hopes that her research will encourage parents and health practitioners to be more vigilant in monitoring children with behavioral problems following TBI.

Both ADHD and secondary ADHD are treated the same way, often with a combination of behavioral therapy and medication.

What can be problematic is diagnosing the disorder before it becomes an issue, which can lead to academic or social dysfunction.

Dr. Mark Wolraich, professor of pediatrics at Oklahoma University Health Sciences Center and the director of the Child Study Center, speaking on behalf of the American Academy of Pediatrics, told Healthline that this research would be helpful to that end.

“Probably the main thing is getting a good [medical] history, determining if they’ve had any TBI. One of the things that should be monitored is how well they are functioning, how are they doing in school, or are they getting into trouble in terms of their behaviors. ADHD should be thought of as one of the possible causes of that,” he said.

“It’s more monitoring them so that they don’t have a significant period of failure and getting in trouble before people think that something is going on,” he added.