Research Review

Alzheimer’s Cognitive Decline Slows in Advanced Age

The greatest risk factor for Alzheimer’s disease (AD) is advancing age. By age 85, the likelihood of developing the dreaded neurological disorder is roughly 50%. But researchers at the University of California (UC), San Diego School of Medicine say AD hits hardest among the “younger elderly”—people in their 60s and 70s—who show faster rates of brain tissue loss and cognitive decline than AD patients aged 80 and older.

The findings, reported online in PLOS One, have profound implications for both diagnosing AD and efforts to find new treatments. There is no cure for AD and existing therapies do not slow or stop disease progression.

“One of the key features for the clinical determination of AD is its relentless progressive course,” says Dominic Holland, PhD, a researcher at the department of neurosciences at UC San Diego and the study’s first author. “Patients typically show marked deterioration year after year. If older patients are not showing the same deterioration from one year to the next, doctors may be hesitant to diagnose AD, and thus these patients may not receive appropriate care, which can be very important for their quality of life.”

Holland and colleagues used imaging and biomarker data from participants in the Alzheimer’s Disease Neuroimaging Initiative, a multi-institution effort coordinated at UC San Diego. They examined 723 people, aged 65 to 90, who were categorized as either cognitively normal, with mild cognitive impairment (an intermediate stage between normal, age-related cognitive decline and dementia) or suffering from full-blown AD.

“We found that younger elderly show higher rates of cognitive decline and faster rates of tissue loss in brain regions that are vulnerable during the early stages of AD,” says Holland. “Additionally cerebrospinal fluid biomarker levels indicate a greater disease burden in younger than in older individuals.”

Holland says it’s not clear why AD is more aggressive among younger elderly.

“It may be that patients who show onset of dementia at an older age, and are declining slowly, have been declining at that rate for a long time,” says coauthor Linda McEvoy, PhD, an associate professor of radiology. “But because of cognitive reserve or other still-unknown factors that provide ‘resistance’ against brain damage, clinical symptoms do not manifest till later age.”

Another possibility, according to Holland, is that older patients may be suffering from mixed dementia—a combination of AD pathology and other neurological conditions. These patients might withstand the effects of AD until other adverse factors, such as brain lesions caused by cerebrovascular disease, take hold. At the moment, AD can only be diagnosed definitively by an autopsy. “So we do not yet know the underlying neuropathology of participants in this study,” Holland says.

— Source: University of California, San Diego Health Sciences