A mixture of brain ailments, as opposed to just one condition, might be driving dementia, new research found.
In this study, the researchers wanted to further examine how mixed pathology can lead to dementia. Previous studies have suggested that a blend of multiple conditions contributes to the development of the neurodegenerative disease but none of the studies had provided a set of data that was comprehensive enough to support this disease progression model.
"Even the lay public seems to now be appreciating that dementia is often the result not of a single disease process, but of a combination," said lead investigator Dr. Lon White, from the University of Hawaii and the Veterans Affairs-affiliated Pacific Health Research and Education Institute.
White and his colleagues analyzed data taken from two long-term studies that tracked hundreds of aging adults via multiple cognitive tests and conducted post-mortem brain autopsies. The two studies included 334 Roman Catholic nuns and 774 Japanese American men. The average age of death was about 90 in the Nun Study and 88 in the Honolulu-Asia Aging Study.
After examining the participants' brain autopsies, the researchers found that about 50 percent of the brains had signs of Alzheimer's. The researchers noted that not all of the Alzheimer's afflicted brains had the same lesion type. In only half of this group, the researchers could categorize the disease as the main lesion type.
When the researchers looked at the 279 participants with severe Alzheimer's pathology, however, at least 75 percent of them had one or more other types of lesions. In other participants who experienced cognitive decline, their brains did not have any signs that would point to Alzheimer's.
Based on the differences between the participants, the researchers concluded that dementia is most likely caused by multiple conditions. The researchers added that a greater combination of ailments was associated with a more dramatic effect on a participants' dementia risk.
"I believe it's because all of these lesion types seem to be broadly distributed around the brain, each involving different neuron types and fields. So the result of their summation reflects the wiping out of multiple different systems within the brain, each required for optimal cognition," White explained. "The bad news is that it is much worse to have comorbid lesions than to have a single lesion type."
The researchers were able to identify five varying brain pathologies that could all cause dementia. These pathologies were Alzheimer's disease, hippocampal sclerosis, microinfarcts, low brain weight and Lewy bodies. They argued that researchers could potentially develop better treatments for dementia by targeting the different brain pathologies.
The study was published in the journal Neurology.
