Blood Vessel Disease Causes Third Of Dementia
Here's yet another reminder that aging isn't just about creaky bones, gray hair, and wrinkled skin. Brain damage caused by lots of small strokes might account for a third of all old age dementia. Dementia isn't dignified and it doesn't make you wise.
Alzheimer's disease may be what most people fear as they grow older, but autopsy data from a long-range study of 3,400 men and women in the Seattle region found that the brains of a third of those who had become demented before death showed evidence of small vessel damage: the type of small, cumulative injury that can come from hypertension or diabetes.
Dr. Thomas Montine, University of Washington, presented the study results at Experimental Biology 2008 in San Diego on April 6. His presentation was part of the scientific program of the American Society for Biochemistry and Molecular Biology (ASBMB).
In the autopsied brains of people who had experienced cognitive decline and dementia, 45 percent of the risk for dementia was associated with pathologic changes of Alzheimer's disease. Another 10 percent of dementia risk was associated with Lewy bodies, neocortical structural changes that indicate a degenerative brain disease known as Lewy Body Dementia, believed by some clinicians to be a variant of Alzheimer's and/or Parkinson's disease. But a third of the risk for dementia (33 percent) was associated with damage to the brain from small vessel disease.
Dr. Montine and his colleagues believe that, and are now studying in more detail, this small vessel damage is the cumulative effect of multiple small strokes caused by hypertension and diabetes, strokes so small that the person experiences no sensation or problems until the cumulative effect reaches a tipping point. This may be good news, says Dr. Montine. At a time when prevention and treatment for Alzheimer's remain investigational, methods for preventing complications of hypertension and diabetes are currently available.
My guess is that the estimate of a third of all dementia as caused by blood vessel problems might be an underestimate. Other brain aging diseases might develop in part due to poor circulation reducing nutrition to brain cells.
On the bright side, stem cell therapies that repair blood vessels will some day slow brain aging by avoiding accumulation of stroke damage. Better blood vessels will keep the brain better fed and undamaged by blood vessel ruptures.
Dr. Montine may be right, but it's hard to be certain. At one time vascular disease was considered to be the major cause of dementia, then it went out of fashion, but now it's back. The problem is that none of these changes are absolutely specific for dementia. The changes of Alzheimer's disease also occur in non-demented elderly people, but in lesser amounts:
The confirmation of a diagnosis of AD is made at autopsy. The pathognomonic microscopic feature of AD is an increased number of neuritic plaques in the cerebral cortex. These neuritic plaques are composed of tortuous neuritic processes surrounding a central amyloid core. Reactive astrocytes and microglia may appear at the periphery of these plaques. Though plaques may easily be found in the hippocampus, their presence in increased numbers in neocortex is necessary for a diagnosis of AD. The amyloid core consists primarily of a small peptide known as Aß which is derived from the larger amyloid precursor protein (APP). Plaques that have the amyloid proteins but lack the neuritic processes are known as diffuse plaques, which do not count toward the diagnosis of AD. Since the number of plaques increases with age, the number needed for diagnosis of AD is age-dependent. Other histologic features of AD include neurofibrillary tangles, amyloid angiopathy, and granolovacuolar degeneration.
And so it is with small vessel disease - it also occurs commonly in elderly people without dementia and is increased in conditions such as diabetes and hypertension. I think Dr. Montine is probably right - it probably does play a major role in many cases of dementia. However, in order to prove this, it would be necessary to demonstrate a higher level of small vessel disease in demented individuals who do not have Alzheimer's disease as compared to an age-matched control group with no dementia. Of course, these conditions may coexist, and clinical dementia may be the final common pathway for a number of underlying conditions, including small vessel disease, Alzheimer's disease and Parkinson's disease/Lewy body dementia.
And so it is with small vessel disease - it also occurs commonly in elderly people without dementia...
Many elderly people have some degree of mental or intellectual disability, even though it's not severe enough to qualify as dementia. If the cognitive and memory impairments associated with "normal" aging were quantified in IQ terms, it's quite possible that a correlation would be found with the amount of amyloid plaques or small vessel damage in the brain.