More than fifty percent of patients with traumatic brain injury, experience depression in the year following their injury.
Researchers led by Charles Bombardier of the University of Washington School of Medicine in Seattle found that 53 percent of patients with traumatic brain injury, or around eight times the rate in the general population, suffered major depression at least once in the year following their injury.
But fewer than half the study participants -- 44 percent -- received antidepressants or counseling for their depression.
"Traumatic brain injury (TBI) is a major cause of disability in the United States and a signature injury among wounded soldiers," the researchers said in a study published in a special mental health issue of the Journal of the American Medical Association said.
"Major depressive disorder (MDD) may be the most common and disabling psychiatric condition in individuals with TBI," the study said.
The researchers looked at 559 adults in hospital, most of them men who had been in a car accident, the second most common cause of TBI in the United States after falls, according to the Centers for Disease Control and Prevention (CDC).
Among the military, blast injuries are a significant cause of TBIs, according to the US Department of Defense's Deployment Health Clinical Center.
A 2008 RAND corporation report showed that around one in five US service members reported sustaining a possible traumatic brain injury while deployed in Iraq or Afghanistan, and seven percent said they had probable TBI along with post-traumatic stress disorder or depression.
The patients who took part in the study were followed up by telephone to assess their mental health at one, six, eight, 10 and 12 months after their accident.
Those who reported feeling depressed in the year after sustaining a traumatic brain injury were more likely to show signs of anxiety or aggression, have poorer cognitive functioning, poor recovery and higher rates of suicide attempts than the non-depressed group, the study said.
And yet, major depression remains "an invisible disorder within an often invisible injury," the study said, calling for "aggressive efforts" to educate clinicians about the importance of depression in patients with post-TBI depression, and improved detection methods and care.
Traumatic brain injury is defined as a blow or jolt to the head, or a penetrating head injury that disrupts the function of the brain.
Around 1.4 million people sustain a traumatic brain injury each year in the United States. Of those 50,000 die and 235,000 are hospitalized, according to CDC figures.