This truly is a big deal. The accuracy of the clinical and MRI diagnosis of Alzheimer’s, even by experienced specialists, is no better than 80%. Disorders that can be mistaken for Alzheimer’s are many, especially vascular (strokes), Lewy body dementia, and frontotemporal degeneration. PET scans (expensive) and spinal fluid analysis (invasive) detect amyloid and tau deposition in the brain. Their usefulness is limited by the fact that a third of cognitively normal elderly people have amyloid deposition but never progress to dementia because of adequate brain reserve, determined by educational achievement.
Even though there is currently no treatment proven to prevent or slow the progression of Alzheimer’s, an accurate blood test can prevent “contamination” of clinical trials. Patients and families would not have to wait for an autopsy for a confident diagnosis.
The blood test measures plasma p-tau181 and is sensitive across the entire Alzheimer’s disease continuum. It is not yet commercially available but almost certainly will be. It will be transformative when a disease-modifying treatment is found.
See the article by Thomas K Karikari et al and the editorial by Clifford R Jack, Jr in Lancet Neurology, Volume 19, May 2020.
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