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.