Exploring the link between traumatic brain injury and Attention Deficit Hyperactivity Disorder
Traumatic brain injury (TBI) is a growing problem in the United States. Parents whose children engage in group sports (which account for a large portion of pediatric TBIs) may be particularly concerned by the risks associated with this kind of injury.
Each year, approximately half a million children under the age of 14 are admitted to emergency rooms for TBI, and though the majority of these incidents are classified as mild TBIs, they are still often associated with long-term symptoms that can disrupt development and cognition throughout childhood and later in life.
Research suggests that there may be a link between a history of TBI and the development of attention deficit hyperactivity disorder (ADHD). ADHD is a neurological and behavioral condition that is characterized by inattention, hyperactivity, and impulsive behavior. ADHD typically becomes apparent in childhood, and though the symptoms of ADHD lessen for some children as they mature, about two-thirds of children with ADHD continue to have symptoms throughout adulthood.
Post-concussive symptoms (PCS), which are symptoms that occur after a TBI and persist for a year or more, bear many similarities to ADHD. For instance, among the most disruptive PCS are cognitive disturbances such as memory deficits and problems with attention and focus. A 2015 study identified a positive association between TBI and past or present history of ADHD. In this study, researchers conducted a telephone survey to contact 4,000 adults who had experienced a TBI. They found that about 7% of their study population that had experienced a TBI met the criteria for ADHD, and about 6% of people with TBI had been diagnosed with ADHD earlier in life. This finding raises the question: Does TBI cause ADHD, or does ADHD increase the risk for TBI?
One potential explanation for this association is that TBI causes neuropsychological changes that cause the development of ADHD. This is referred to as secondary ADHD. A 2018 study sought to understand the risk factors associated with the development of secondary ADHD. Researchers performed ADHD evaluations on 187 children ages 3-7 who had no pre-injury history of TBI. They found a significantly higher prevalence of ADHD after TBI, ranging from 20% in the case of mild TBI to more than 60% in the case of severe TBI. They also found that the onset of ADHD can occur several years following injury.
Some experts disagree as to whether ADHD can develop as the result of a head injury, or whether ADHD is a genetically predisposed developmental disorder and therefore, by definition, cannot be caused by an acute injury such as TBI. Research does indicate that ADHD is a genetic disorder: several genes have been implicated in the development of ADHD, and it tends to run in families, which supports a genetic model. But the similarities between PCS and ADHD do support the idea that TBI causes ADHD-like symptoms to develop.
An alternative hypothesis is that ADHD is a risk factor for TBI. ADHD causes impulsivity and erratic behavior, which predispose individuals to experience injuries, including TBI. Furthermore, a 2015 study that examined the association between TBI and ADHD found that ADHD is an antecedent risk factor for TBI; that is, the presence of ADHD increases the risk of developing TBI, and also increases complications related to TBI if this kind of injury does occur. In this study, researchers compared children with ADHD who had experienced mild TBI; children without ADHD who had experienced a TBI; and children with and without ADHD who had not experienced a TBI. They found that the children with TBI had a higher rate of ADHD than the children without TBI, but that, importantly, that ADHD onset was earlier than the TBI. This study supports the idea that differences in the brains of children with ADHD put children with ADHD at a higher risk (than typically-developing children) for developing TBI after head injury.
The relationship between ADHD and TBI is complex, and the issue requires further research to determine the direction of causality. In general, children with ADHD and children who engage in athletic activities are at higher risk for experiencing TBI, and parents are advised to be vigilant for symptoms of TBI in their children.
Biederman J et al. Mild traumatic brain injury and attention-deficit hyperactivity disorder in young student athletes." The Journal of Nervous and Mental Disease, 203.11 (2015): 813.
Ilie G et al. The association between traumatic brain injury and ADHD in a Canadian adult sample. Journal of Psychiatric Research, 69 (2015): 174-179.
Narad ME et al. Secondary Attention-Deficit/Hyperactivity Disorder in children and adolescents 5 to 10 years after traumatic brain injury. JAMA Pediatriacs. Published online March 19, 2018. doi:10.1001/jamapediatrics.2017.5746