New Thinking About Alzheimer’s Dementia
Since the beginning of recorded history of global populations, infants and young children have outnumbered older adults.
We are now at the equal crossroads and have begun to reverse this trend. By 2050, the global population will have 15-18% older adults and only 6-8% infants and young children. Many of these older adults will suffer from age-related cognitive disorders, the most common being Alzheimer’s dementia.
The present societal impact of Alzheimer’s dementia totals three billion dollars annually. This number will increase to 1.1 trillion dollars by 2050 unless a cure or better treatment for Alzheimer’s dementia is found.
The diagnosis of Alzheimer’s dementia is made on clinical grounds after extensive history of the illness is obtained from the patient along with a detailed neurological examination of the patient, brain imaging, laboratory tests and neuropsychological testing. The definitive diagnosis can only come from tissue at autopsy or with a brain biopsy, which is not commonly obtained.
The exact cause of Alzheimer’s dementia is not known. It is speculated that the disorder is produced by an unknown chain of events caused by the deposit of an otherwise normal protein called amyloid.
This protein becomes a toxic form and is deposited extracellularly causing an additional chain reaction within the neurons, characterized by the production of an additional second protein called tau, which ultimately causes the neuronal death. As a result of these changes in the brain, numerous biomarkers have been discovered allowing for better diagnostic accuracy in dealing with persons suffering from or suspected of having Alzheimer’s dementia.
Recently, biomarkers have been discovered and have increased the accuracy of the diagnosis of Alzheimer’s dementia in the living patient. These biomarkers increase in accuracy allowing for earlier detection of possible Alzheimer’s dementia patients and will improve experimental research looking for better treatments of such patients.
Today, there are four available biomarkers used to aide in the diagnosis of Alzheimer’s dementia.
The first is a cerebral spinal fluid evaluation for two substances; one is beta amyloid and the other is tau protein, both are the abnormal proteins seen in patients with Alzheimer’s disease and contribute to the pathogenesis of the disorder. These biomarkers are obtained from a lumbar puncture or spinal tap in order to obtain a sample of cerebral spinal fluid.
The second biomarker is an amyloid PET scan. This is a form of brain imaging where a harmless radioactive product is injected intravenously and accumulates in the brain attaching to the abnormal amyloid molecule.
The third biomarker is also a PET scan, but uses a glucose marker FDG. This PET scan records metabolism in the living cells of the brain. The patterns of changes are very characteristic in patients with Alzheimer’s disease.
The fourth biomarker is magnetic resonance imaging scanning of the brain, looking for atrophy in the two important areas of known atrophy found in patients suffering from Alzheimer’s disease; the hippocampus and the posterior parietal lobes.
There are five identified stages of Alzheimer’s dementia; preclinical, mild cognitive impairment, mild dementia, moderate dementia and severe dementia. The preclinical stage of Alzheimer’s dementia begins 15-20 years prior to any clinical symptoms. Although asymptomatic, these preclinical Alzheimer patients may already have abnormal amyloid deposits in their brains. These deposits can be shown by both the CSF assessment as well as a positive amyloid PET scan. In the next stage, mild cognitive impairment, the person frequently notices mild memory difficulty, especially short-term memory as well as thinking and learning. However, these symptoms do not interfere with activities of daily living. It should be noted that not everyone suffering from mild cognitive impairment will develop a dementia.
Some patients are suffering from temporary medical conditions which can be corrected and/or a depression, which can be treated. Although there is no cure for Alzheimer’s dementia, there are now better biomarker indicators allowing for earlier identification of likely persons suffering from Alzheimer’s dementia.
These biomarkers will allow researchers to set up experimental drug trials for preclinical and early Alzheimer patients rather than attempting to use only patients with advanced Alzheimer’s dementia. Clearly, the earlier intervention therapy is started in a patient with suspected Alzheimer’s dementia, the greater the chance of achieving a positive response. In the future, as biomarker research advances, we should discover a simple blood test that can be used to screen and diagnose patients with potential Alzheimer’s dementia. We should then be able to start treatment aimed at reducing the likelihood of developing clinically evident Alzheimer’s dementia at the earliest point possible.
Dr. H. Murray Todd is the medical director of Broward Health North’s Neurological Institute and Memory Disorder Center. He can be reached at firstname.lastname@example.org or (954) 786-7341.