Many different diseases
may produce symptoms of dementia - defined as cognitive decline and impaired
memory - in aged persons. Although Alzheimer's disease is probably the most
recognized cause of dementia, HS-AGING also causes serious cognitive impairment
in older adults. In those who live to a very advanced age (beyond the age of
95) HS-AGING is roughly as prevalent as Alzheimer's.
It is important for
physicians and scientists to understand the unique pathology of HS-AGING, and
to be able to differentiate it from other diseases, as it is only by making an
accurate diagnosis that clinicians can hope to treat people who present with
signs of cognitive decline.
What is HS-Ageing?
HS-Ageing stands for “Hippocampal Sclerosis in
Ageing People”. Both Alzheimer’s and HS-Ageing are different types of dementia.
In people aged 65 to 95, 60% of dementia cases are Alzheimer’s. That is
why Alzheimer’s is so well-known. At age 95, the balance shifts and HS-Ageing
becomes about as common as Alzheimer’s. And when dementia is seen in the
elderly, the default diagnosis is Alzheimer's. This is caused by many factors,
among them:
- Patients
often do not want to go through extensive testing for a variety of
reasons.
- There
is no simple test. The differences between dementias can be subtle.
Therefore, distinguishing between dementias is often technically
challenging.
- Cost
comes into play. For example, F18 dementia scans can run thousands of
dollars. Therefore, many a diagnosis is made based on incomplete
information.
With these realities, it is common for a diagnosis
to default to the most common dementia, which is Alzheimer's. As a result,
people with dementias such as HS-Ageing often live out their lives thinking
they have Alzheimer's.
How does HS-Ageing differ from
Alzheimer’s?
Alzheimer’s and HS-Ageing both damage the
hippocampus. It seems that HS-Ageing hits harder than Alzheimer’s, causing
greater disturbances to memory.
HS-Ageing puts a brain under attack from a protein
called TDP-43. It causes sclerosis, or the hardening of tissues. In the case of
HS-Ageing, TDP-43 proteins harden brain tissue in the hippocampus (sometimes
called the memory-processing center), causing the loss of a large number of
crucial brain cells. It is called Hippocampal Sclerosis because the brain’s
hippocampus is the focus of the attack.
Alzheimer’s, on the other hand, is an attack on the
brain by plaques (made from beta-amyloid) and tangles (made of tau proteins).
Researchers speculate that the plaques clump together and “choke” brain cells,
while the tangles strangle them from within.
How does HS-Ageing differ from regular
HS?
Regular Hippocampal Sclerosis (HS) occurs in younger
people where brain tissue hardening is associated with epilepsy. HS-Ageing is a
similar hardening, but it occurs in the elderly with different consequences. It
is caused by a long life of physical wear-and-tear on the brain, similar to vascular
dementia. As a matter of fact, once people hit 95, the combined occurrence of HS-Ageing
PLUS vascular dementia actually outstrip Alzheimer’s.
Why does the type of dementia matter?
As explained above, the biochemistry of each
dementia differs significantly. This implies different medications are required
to fight the chemicals causing the dementia. A person’s response to medicines
and supplements will be entirely different, depending on the disease.
Importantly, new F18 imaging techniques have
recently been introduced that let doctors see if a person with dementia has the
plaques associated with Alzheimer's. Using this technique helps doctors tell
the difference between Alzheimer’s and HS-Ageing. This is particularly crucial
in the world of clinical trials, where participants must closely match the
experimental drugs they are testing.
Research
It is important for physicians and scientists to
understand the unique pathology of HS-AGING, and to be able to differentiate it
from other diseases, as it is only by making an accurate diagnosis that
clinicians can hope to treat people who present with signs of cognitive
decline.
Nelson, a neuropathologist, analyzed autopsy data
from 1,100 individuals (2011), each with substantial clinical data available
from before death. The long-term clinical information was obtained through the
University of Kentucky Alzheimer's Disease Center, the Nun Study and the
Georgia Centenarian Study (all autopsies were performed at the University of
Kentucky). The large numbers of patients and the high quality of the data
enabled the research team to gather new clues about the prevalence and impact
of HS-AGING.
"We and others have shown previously that
HS-AGING has a strong impact on cognition. The goal of the new study was to
define HS-AGING as a distinct disease entity," said Nelson.
"There were some surprises. The high prevalence
of HS-AGING in individuals older than 95 was unexpected. In addition, by
analyzing neuropathological data alongside clinical data, we were able to
determine that there is a recognizable cognitive profile for individuals likely
to develop HS-AGING," said Nelson.
In the future, clinicians may be able to utilize
cognitive tests with increased accuracy to differentiate a diagnosis of
HS-AGING from a general diagnosis of cognitive decline. Being able to pinpoint
the cause of cognitive decline may lead to better and more accurate diagnosis
and treatment of aging individuals who present with signs of dementia.
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