Biomarkers for Dementia
At this year's American Academy of Neurology's annual meeting, the discussion was focused on examining important biomarkers and their significance for diagnosing dementia. Dementia is a general term that often relates to a number of neurodegenerative disorders that often influence a person's memory and personality. Alzheimer's disease is the most common of the dementias. Traditionally, dementia has been diagnosed by ruling out other possible causes. In addition, typically the only way to fully provide diagnostic assurance of dementia is through autopsy.
However, recently new tests and biomarkers have been discovered that can provide greater assurance of diagnostic accuracy. These tests and biomarkers are not without a cost, however, both financially and psychologically. Therefore, even though science has progressed to provide use with a greater level of illumination into a clearer and more valid diagnosis, the question can be raised whether 1. they provide any greater efficacy for medical intervention since no cures exist for these illnesses; 2. the potential for false positives to exist can lead to psychological harm to the person receiving incorrect information; and 3. the potential for augmenting already exorbitant health costs, while not giving commensurate benefits to the patient. This is classic example of practicing medicine with no clear goals in which the means becomes the end in itself.
At the conference, three important biomarkers raised considerable interest. Hippocampal atrophy, decreased cerebral spinal fluid amyloid, and decreased brain glucose metabolism appeared to have a positive and cumulative association for dementia. In other words, those that had these biomarkers were more likely to progress to dementia, with those having all three being the most likely to eventually have a diagnosis of dementia. In fact, in one of the studies cited, only four percent of the individuals that failed to have any of the biomarkers progressed to dementia. However, 100 percent of those in the study that had all three biomarkers eventually acquired dementia.
An important consideration raised by many members at the convention was that there needs to be a standardized way to measure the biomarkers. This would enhance the validity of the tests as well. In fact, how biomarkers are measured may be more important than the type or amount of biomarkers used. Since there is so much variability currently in how many of these biomarkers are measured, this in itself can introduce considerable levels of error and reduce the accuracy of the testing.
It was found that an important biomarker, a positive amyloid beta marker, had a significant predictive validity for determining the progression of future cases of dementia. Among those that had a positive amyloid beta marker, 82% progressed to Alzheimer's disease compared with only 0 to 7% of those that were amyloid beta negative. However, 20 to 40% of the elderly who do not have any diagnosis of dementia also have amyloid plaques and are therefore positive for a amyloid marker and yet do not have any visible signs or symptoms of dementia.
Therefore, one has to weigh the costs and benefits of using such tests for diagnostic purposes. Consider if the tests provide any enhanced ability to provide therapeutic intervention and subsequently enhance the functional significance of a person's life. The argument for using these tests is that one is able to find out who will progress to dementia and therefore start aggressive treatment earlier, possibly before noticeable signs and symptoms appear.
The first concern is given the current levels of treatment for dementia, especially those of the Alzheimer's type, none of which has any cure associated with them, will starting treatment earlier really forestall the progression of the disease to any appreciable level? The second concern is if patients harbor biomarkers that may eventually lead to a particular dementia, this could have a significant psychological toll on the individual. A third issue is that some individuals have these markers but possibly may not have any signs or symptoms of the disease. Fourth, without any cures, does providing greater assurance of a proper dementia diagnosis really hold any significant medical value, especially for the patient?
Often in science, we may lose sight of the true goals, which in this case would be to benefit the person who has one of these dreaded diseases. Yet, if enhanced accuracy in this area fails to promote any potentially greater benefit such as attenuation of the symptoms or eradication of the disease, then the question arises, "Are we just enamored with the technology for measuring a particular biomarker?"
If this is the case, we have lost sight of the ultimate goal, which is to reduce or eliminate the disease. Finally, given the cost of such tests, which can cost thousands of dollars, multiplied by the number of individuals that may potentially get tested, this can augment our annual health care expenses considerably.
Therefore, the question that needs to be answered is whether the benefits of such biomarker tests outweigh the costs that may be incurred. It is difficult to jusitfy the costs given the very few, if any, benefits that may result with our current level of therapeutic knowledge for disease amelioration. This does not mean that the tests don't have any value in more specific cases. Nor does it mean that we as a scientific and medical community should shelve these tests. Currently, the ability to use a curative or significantly ameliorative intervention has not kept pace with our ability to find important biological makers. We have found some very important biomarkers that appear to be strongly associated with dementia may actually be used to enhance our progress toward finding better forms of therapeutic intervention to address these deadly diseases.
The establishment of firmly grounded biomarkers, although not at this time being an important therapeutic breakthrough for the amelioration of disease, may ultimately help to hone our ability in finding important curative interventions.
Stetka, B. S. (2013/April). Alzheimer Biomarkers in Clinical Practice. Medscape News. http://www.medscape.com/viewarticle/781533?src=wnl_edit_specol&uac=87637DR
Read more articles on this topic:
Strategic Plan to Tackle Alzheimer's
Alzheimer's Research Update
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