More Evidence Links Head Trauma to Alzheimer's Pathology

December 27, 2013

Further evidence that head trauma could be associated with Alzheimer's disease later in life has been reported in a new study.

The study, published online in Neurology on December 26, was conducted by a team led by Michelle M. Mielke, PhD, Mayo Clinic, Rochester, Minnesota.

"In our study we found that among older adults with mild cognitive impairment, those who reported having had a head trauma earlier in life were more likely to show brain changes suggestive of Alzheimer's disease. But we didn't find any such association in cognitively normal individuals," Dr. Mielke commented to Medscape Medical News.

"Our results add merit to the idea that concussion and Alzheimer's disease brain pathology may be related. However, the fact that we did not find a relationship in cognitively normal individuals suggests that any association between head trauma and amyloid is complex," she added.

Amyloid Deposition

The researchers report that autopsy studies have reported significant amyloid-β deposition in up to 30% of persons who die acutely following a brain injury, including children. It has also been observed that cerebrospinal fluid levels of amyloid-β are lower, and tau levels higher, immediately after severe traumatic brain injuries.

"Several previous epidemiological studies have looked at the association of head trauma and Alzheimer's," Dr. Mielke noted. "Some have found an association. Some have not."

The current study included 448 cognitively normal individuals and 141 individuals with mild cognitive impairment, all aged 70 to 89 years, from the Mayo Clinic Study of Aging who underwent positron emission tomography (PET) and MRI and were asked about head trauma with at least momentary loss of consciousness or memory earlier in life.

Results showed that 17% of cognitively normal individuals and 18% of those with mild cognitive impairment reported a previous head trauma.

In the cognitively normal population, no neuroimaging measures differed between those with and without head trauma. However, in the cognitively impaired group, amyloid levels were higher among those who reported having had head trauma, by an average 0.36 standardized uptake value ratio units (P = .002).

The researchers offer several possible explanations as to why the results differed between the cognitive normal and impaired groups. One possibility is that because amyloid is a byproduct of the myelin repair process, its deposition occurs only after a critical level of demyelination has occurred.

"Head injury causes shearing of the axons, which some individuals have the capacity to overcome and some do not. The hypothesis is that this causes increased amyloid deposition," Dr. Mielke told Medscape Medical News.

The study was supported by the National Institutes of Health, the Robert Wood Johnson Foundation, the Alexander Family Alzheimer’s Disease Research Professorship, GE Healthcare, the Elsie and Marvin Dekelboum Family Foundation, the MN Partnership for Biotechnology and Medical Genomics, and the Robert H. and Clarice Smith and Abigail van Buren Alzheimer's Disease Research Program.

Neurology. Published online December 26, 2013. Abstract

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