NEW YORK (CNN) -- Sgt. Ryan Kahlor has the same nightmare every time, a vision of walls painted in blood and fat, and men on top of houses, throwing pieces of Marines' bodies off rooftops. It's a vision he can't shake, because he lived through it while deployed to Iraq last year.
Sgt. Ryan Kahlor survived four bomb blasts during his duty in Iraq and suffered concussions.
"I have nightmares. I dwell on it. I think about it all the time," said Kahlor, 24. "Staying asleep is hard. I associate a bed with the dreams I have. My parents think I'm crazy, but I sleep better when I'm on the floor."
Kahlor has post-traumatic stress disorder, which can develop after surviving a traumatic event in which a person is physically threatened or injured.
He also experienced concussions while surviving four explosions during his 14 months in Iraq. He said these events left him with a detached retina, vertigo, memory problems and dizziness.
A new military study published Wednesday in the New England Journal of Medicine says soldiers who suffered concussions in Iraq were not only at higher risk of developing post-traumatic stress disorder and depression, but also that the depression and PTSD, not the head injuries, may be the cause of ongoing physical symptoms.
Five percent of the 2,500 soldiers surveyed by Walter Reed Army Institute of Research said they had concussions in which they lost consciousness during combat. Forty-four percent of these soldiers ended up with PTSD.
Researchers were surprised to find symptoms normally associated with concussions -- headaches, dizziness, irritability and memory problems -- were actually related to PTSD or depression. Watch Dr. Sanjay Gupta explain the study. »
"It isn't the combat exposure or physical injury, it's the PTSD that seems to drive these symptoms. That's a surprise," said Joseph A. Boscarino, Ph.D., who studies PTSD at the Geisinger Center for Health Research in Danville, Pennsylvania. "You would expect they would have these other symptoms related to traumatic brain injury, that maybe they have a permanent injury, but it's explained by whether they have PTSD or depression."
About 8 million American adults have PTSD. A 2003 New England Journal of Medicine Study found that 15 percent to 17 percent of Iraq and Afghanistan veterans were suffering from PTSD, and more than 60 percent of those showing symptoms were unlikely to seek help because of fears of stigmatization or loss of career advancement opportunities.
As of June 30, 2007, the Department of Defense reported 3,294 soldiers in Iraq and Afghanistan suffering from traumatic brain injuries, or TBIs. Bomb blasts caused nearly 70 percent of those TBI cases.
Dr. James Kelly, a neurology professor at the University of Colorado and a co-author of guidelines the military uses to identify traumatic brain injury, expressed concerns that doctors will attribute lingering health problems to psychological issues.
"I think if people misunderstand or overextend beyond what this survey shows, they could dismiss true brain injury features as psychological only," Kelly said. "It would be a terrible disservice to our military for that to happen."
Kahlor is worried this study will make it harder for soldiers to get appropriate medical care.
"The military doesn't want to diagnose people with brain injury," he said. "So what they'll do is play it off as PTSD as the sole injury for everyone, because PTSD and traumatic brain injury have very similar symptoms," he said. "The disability [compensation] is a lot higher for traumatic brain injury. What the military is saying is, you can't be diagnosed from a brain injury unless you get better from PTSD. It's kind of like a paradox."
Kahlor says he has documents saying he has concussion injuries such as a detached retina, seizure activity in the brain, inner-ear expansion and post-concussion syndrome, which gives him bad headaches. Still, he has been unable to get an official diagnosis of traumatic brain injury.
"A doctor in Fort Irwin looked at me and glanced at my records for 10 minutes and wrote on my records that he thought my symptoms, my claims were psychosomatic, where I made them up myself," Kahlor said. "He's basically seen me once. He wanted to send me to a med board to get me out of the Army as soon as possible and pawn me off to the VA system."
In response to concerns that this study could make it more difficult for soldiers to get a diagnosis of traumatic brain injury, study author Col. Charles Hoge said, "Hopefully it clarifies things a bit, that soldiers who have had concussions with loss of consciousness are at higher risk of PTSD. We want to make sure they are seen and get help. It also clarifies that the symptoms they are experiencing may be multiple reasons for that."
Kelly said one of the problems with the study is that it describes symptoms such as headache, dizziness and fatigue as possibly psychosomatic and related to PTSD and depression. But these are symptoms also commonly associated with postconcussive syndrome, he said.
"They don't know that these soldiers didn't have post-concussion syndrome," he said. "They are components of post-concussion syndrome and PTSD... It's absolutely confusing. My concern with this article is people can over-attribute all the lingering problems to psychological issues only, when it started with a biomechanical brain injury. I think it's unfair to unlink what happened to the brain and the psychological aftermath of what happened in that scenario."
In an accompanying editorial, Richard A. Bryant, Ph.D., says this study should encourage doctors to be more cautious when attributing health problems to mild traumatic brain injury, because PTSD and depression may be the problem.
"Incontrovertible evidence now shows that psychological factors play a significant role in postconcussive symptoms," Bryant said.
"Soldiers should not be led to believe that they have a brain injury that will result in permanent change."
He said the study also highlights the need for a clear definition of mild traumatic brain injury.
"The study retrospectively assesses for mild traumatic brain injury by inquiring about having a loss of consciousness, being dazed, or not remembering the inquiry. Each of these reactions can be attributed to acute stress," Bryant said.