Does Head Injury Increase Risk of Alzheimer's Disease?
Oct. 23, 2000 -- Many patients with Alzheimer's disease have a head injury years before they develop the characteristic memory problems, and researchers have long suggested a link between the two conditions. But could it be just a coincidence? Or does head injury in some way trigger changes leading to Alzheimer's disease, or make it appear earlier?
A new study reported in the Oct. 24 issue of Neurology is helping to solve these mysteries, as it shows that head injuries in young men are associated with an increased risk of Alzheimer's disease and other dementias in late life, and the risk goes up when the injury is more severe.
"This study adds a few more pieces to the puzzle in trying to determine the true association between head injury and Alzheimer's disease," study author Brenda L. Plassman, PhD, director of the epidemiology of dementia program at Duke University in Durham, N.C., tells WebMD.
"There is controversy as to whether head injury is a risk factor for Alzheimer's disease or dementia," Carol F. Lippa, MD, tells WebMD. Both conditions are very common -- about 4 million Americans have Alzheimer's disease, and about 2 million Americans each year have a head injury. So by chance alone, there is likely to be some overlap.
Earlier studies examining this question suffered from inaccuracies related to patients with Alzheimer's disease, or their family members, reporting their own history of head injury. "Remembering events that may have occurred 50 years earlier may be fraught with errors," Plassman says, and it is even more difficult when the patient has memory problems. Fewer than 70% of subjects in this study remembered a head injury that was documented in their medical records.
Or the opposite may happen -- a patient with Alzheimer's disease or his family may be searching for an explanation for the condition, and therefore may be more likely to assume that there was an earlier head injury. Or, "when the time frame is immediate and the head injury mild, the injury probably just draws the family's attention to the patient. They then note an early dementia that was not noticed before," says Lippa, a professor and chief of neurology and director of the Memory Disorders Program at the MCP-Hahnemann University in Philadelphia.
This study solved some of these problems by relying on medical records rather than patient or family reports to document head injury. By examining military records of World War II veterans hospitalized during their service for head injury, or for other conditions unrelated to head injury, the researchers found, examined, and did psychological testing on more than 500 veterans with documented head injury, and on more than 1,200 without it.
Severity of head injury was determined from how long the veteran passed out or had no memory of the injury, with mild head injury being less than 30 minutes, moderate between 30 minutes and 24 hours, and severe being longer than 24 hours.