LOS ANGELES - Long before symptoms of Alzheimer's disease become apparent to patients and their families, biological changes are occurring within the brain. Amyloid plaques, which are clusters of protein fragments, along with tangles of protein known as tau, form in the brain and grow in number, eventually getting in the way of the brain's ability to function. These biological changes can be detected early in the course of Alzheimer's disease through positron emission tomography (PET) scan or cerebrospinal fluid analysis. Now, a new study led by Keck Medicine of USC neuropsychologist Duke Han, PhD, associate professor of family medicine (clinical scholar) at the Keck School of Medicine of the University of Southern California suggests that cognitive tests are also able to detect early Alzheimer's in people without symptoms.
"In the last decade or so, there has been a lot of work on biomarkers for early Alzheimer's disease," Han says. "There are new imaging methods that can identify neuropathological brain changes that happen early on in the course of the disease. The problem is that they are not widely available, can be invasive and are incredibly expensive. I wanted to see whether the cognitive tests I regularly use as a neuropsychologist relate to these biomarkers."
Putting neuropsychological measures to the test
Han and his colleagues conducted a meta-analysis of 61 studies to explore whether neuropsychological tests can identify early Alzheimer's disease in adults over 50 with normal cognition. The study, which was published in Neuropsychology Review, found that people who had amyloid plaques performed worse on neuropsychological tests of global cognitive function, memory, language, visuospatial ability, processing speed and attention/working memory/executive function than people who did not have amyloid plaques.
The study also found that people with tau pathology or neurodegeneration performed worse on memory tests than people with amyloid plaques. Amyloid plaques and tau pathology were confirmed by PET scan or cerebrospinal fluid analysis.
"The presumption has been that there would be no perceivable difference in how people with preclinical Alzheimer's disease perform on cognitive tests. This study contradicts that presumption," Han says.
Routine cognitive screenings: A new normal?
Han believes that the study results provide a solid argument for incorporating cognitive testing into routine, annual checkups for older people.
"Having a baseline measure of cognition before noticing any kind of cognitive change or decline could be incredibly helpful because it's hard to diagnose early Alzheimer's disease if you don't have a frame of reference to compare to," Han said. "If people would consider getting a baseline evaluation by a qualified neuropsychologist at age 50 or 60, then it could be used as a way to track whether someone is experiencing a true decline in cognition in the future."
Early detection could be a powerful tool to manage Alzheimer's, Han says, giving people precious time to try different medications or interventions that may slow the progression of the disease early on.
"While there's no cure for Alzheimer's disease, the earlier you know that you're at risk for developing it, the more you can potentially do to help stave off that diagnosis in the future," Han says. "For example, exercise, cognitive activity and social activity have been shown to improve brain health."
An estimated 5 million people in the United States have Alzheimer's, and that number could reach 16 million by 2050, according to the Alzheimer's Association.
ABOUT THE KECK SCHOOL OF MEDICINE OF USC
Founded in 1885, the Keck School of Medicine of USC is among the nation's leaders in innovative patient care, scientific discovery, education, and community service. It is part of Keck Medicine of USC, the University of Southern California's medical enterprise, one of only two university-owned academic medical centers in the Los Angeles area. This includes the Keck Medical Center of USC, composed of the Keck Hospital of USC and the USC Norris Cancer Hospital. The two world-class, USC-owned hospitals are staffed by more than 500 physicians who are faculty at the Keck School. The school today has approximately 1,650 full-time faculty members and voluntary faculty of more than 2,400 physicians. These faculty direct the education of approximately 700 medical students and 1,000 students pursuing graduate and post-graduate degrees. The school trains more than 900 resident physicians in more than 50 specialty or subspecialty programs and is the largest educator of physicians practicing in Southern California. Together, the school's faculty and residents serve more than 1.5 million patients each year at Keck Hospital of USC and USC Norris Cancer Hospital, as well as USC-affiliated hospitals Children's Hospital Los Angeles and Los Angeles County + USC Medical Center. Keck School faculty also conduct research and teach at several research centers and institutes, including the USC Norris Comprehensive Cancer Center, the Zilkha Neurogenetic Institute, the Eli and Edythe Broad Center for Stem Cell Research and Regenerative Medicine at USC, the USC Cardiovascular Thoracic Institute, the USC Roski Eye Institute and the USC Institute of Urology.
In 2017, U.S. News & World Report ranked Keck School of Medicine among the Top 40 medical schools in the country.
For more information, go to keck.usc.edu.
Twenty-seven percent of this project's funding ($2,000 in salary support) was funded by the National Institutes of Health under award number K23AG040625. Seventy-three percent of the project's funding ($5,495) was not federally funded. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health.