As I’ve said in previous blogs, Alzheimer’s is a disease that can only be diagnosed after death. A patient with dementia must die and have an autopsy before doctors can be certain they have Alzheimer’s. Currently, there is no test to say for sure a patient with dementia has Alzheimer’s. Most people are diagnosed with Alzheimer’s only after all other causes are eliminated. Thus, if the patient doesn’t have dementia as the result of a stroke, vascular brain disease, alcoholism, Parkinson’s disease, or a host of other causes, the diagnosis, by exclusion, is Alzheimer’s disease. Doctors never are 100% certain, however, until the pathologist examines the brain at autopsy.
At the risk of getting too esoteric, I must state there are two changes in the brain tissue that determine for certain the patient had Alzheimer’s disease. They are:
- Neurofibrillary tangles
- Senile plaques
These abnormalities can be found only by microscopic examination of the brain at autopsy. Any time a patient is suspected of Alzheimer’s, they must have these findings to accurately say they had it.
Neurofibrillary tangles are caused by the accumulation of an abnormal protein within the brain cells. This protein substance is called Tau protein. Normal brain cells do not contain Tau protein.
Senile plaques are an accumulation of a substance called Amyloid protein on the surface of brain cells. Normal brain cells do not have Amyloid protein plaques, either.
To confirm the diagnosis of Alzheimer’s, both of these abnormalities need to be present when the pathologist examines the deceased patient’s brain tissue under the microscope. At least, that was up until recently.
A report in the Journal of the American Medical Association (JAMA) stated the FDA has just approved a new drug (Tauvid) that will detect Tau Protein in the brains of patients being evaluated for dementia. Adults with cognitive impairment (dementia) are given this drug intravenously. The brain is then scanned with a PET Scanner (Positron Emission Tomography). If there is Tau protein in the brain cells, the drug binds to sites in the brain where it is located, and it shows up on the PET scan image. Alzheimer’s disease is the most likely cause of this abnormality.
Researchers in two studies gave Tauvid to 315 terminally ill dementia patients prior to death. The results of their PET scans were compared to findings at autopsy. In the two studies, there was a 92% and 87% correlation between the PET scan and autopsy results.
This means that now doctors have a drug that can be used to confirm the diagnosis of Alzheimer’s in patients with severe dementia while the patient is still alive. Researchers do state that the patients studied had advanced dementia and Tau protein was plentiful and thus easier to detect. They caution doctors that patients with early-onset dementia may not as easily show evidence of the Tau protein abnormality.
Dr. G’s Opinion: I think this is good news for patients with dementia and for their loved ones. There’s a good chance Alzheimer’s disease can be diagnosed earlier. But unless medical science develops an effective treatment that reverses the course of Alzheimer’s dementia, this is merely a novel idea. Yes, it’s great to be able to diagnose Alzheimer’s early, but if you can’t do anything about it, what difference does it make? It will, however, confirm that you have excluded any possibly reversible dementia.
References: Perl DP, Neuropathology of Alzheimer’s Disease. Mt Sinai J Med 2010; 7(1):32-42.
News From the Food and Drug Administration.”The new diagnostic agent detects Tau pathology in the brain” JAMA 2020 Jul 7;324(1):19.
