Concussions among combat soldiers in Iraq were strongly associated with post-traumatic stress disorder several months after the soldiers returned home, according to a new study.

Soldiers who reported losing consciousness from a concussion -- also known as mild traumatic brain injury -- were especially likely to meet the criteria for PTSD, according to the study, published today in the New England Journal of Medicine.

The findings suggest that health problems exhibited by soldiers who have had concussions may be due to co-existing PTSD, "not to lingering brain injury," said Dr. Charles Hoge, the study's lead author and director of psychiatry and neuroscience at the Walter Reed Army Institute of Research.

Researchers also linked some of those health problems to depression. Only one problem, headache, was specifically associated with concussion.

Dr. Joseph Boscarino, an investigator at Geisinger Health System in Danville, said more study is needed, noting the findings are based on self-reported survey data.

But he said the results are good news, in part because they suggest that many of the concussions did not cause permanent neurological damage.

Soldiers who suffered concussions likely were at risk for PTSD because the injuries often occurred under stressful battlefield conditions, Dr. Hoge said.

Compared to soldiers in the study with other injuries, those who reported concussions were significantly more likely to report high combat intensity, blast injury, more than one exposure to an explosion, and hospitalization during deployment.

Researchers analyzed survey responses from 2,525 soldiers from two Army combat brigades. Members of the units were surveyed three to four months after their return from a year in Iraq.

Soldiers were considered to have a mild traumatic brain injury if they reported losing consciousness, not remembering the injury, being dazed or confused or "seeing stars."

About 5 percent of respondents reported injuries with loss of consciousness, while 10.3 percent reported other changes in mental status, such as being dazed or confused. Another 17.2 percent reported other injuries.

Of those reporting loss of consciousness, 43.9 percent met the criteria for PTSD, compared to 27.3 percent of those reporting other changes in mental status, 16.2 percent of those with other injuries, and 9.1 percent of those with no injury.

Because of improved protective equipment, more soldiers are surviving injuries that would have been fatal in earlier conflicts, the study noted.

But concerns also have been raised about the possible long-term effect of concussions, particularly those related to explosions. Researchers said many troops who suffer the injuries reportedly have irritability, memory problems, headache, difficulty concentrating or other symptoms.

Dr. Edward Kendjelic, a neuropsychologist at the VA Pittsburgh Healthcare Center, said treatments for those injuries or PTSD could include medication, psychotherapy or retraining.

At VA Pittsburgh, many returning veterans who seek help for suspected PTSD or other behavioral issues can be seen on a walk-in basis, he noted.

The health system also has begun screening returning veterans for traumatic brain injury. Veterans who screen positive are offered follow-up appointments in 30 days or less, he said.

The VA began implementing the screenings last April, said Dr. Barbara Sigford, national director for physical medicine and rehabilitation for the Veterans Health Administration, which provides VA health care.

She said the four-question screen asks veterans who appear for clinical care whether they were exposed to a blast, were wounded or had other problems, such as a fall or motor vehicle accident; whether the incident resulted in altered consciousness; whether they had new or worsening symptoms; and whether they continue to have those health problems.

Officials said that by the end of October, more than 61,000 veterans had been screened, and about one in five tested positive for traumatic brain injury symptoms. Those who did were to undergo further testing to determine if they suffered such an injury or whether their symptoms were due to other causes, such as PTSD.

A report to the Army Surgeon General by a Traumatic Brain Injury Task Force, released earlier this month, noted that the military also has taken a number of steps to improve care, including screening and documentation of all soldiers exposed to explosions.