For older adults, the progression from normal cognition to mild cognitive impairment to Alzheimer’s disease (AD) varies in both timing and severity. Unseen for years in everyday life, the brain of someone with AD may change slowly and subtly until symptoms become obvious to spouses, children, or friends and which may lead to the person seeking help form a doctor. Recent approaches to developing treatments for AD all emphasize early intervention and hence finding reliable methods to diagnose these changes early in their onset would give physicians and patients more options to manage the disease as well as other forms of dementia, which affects 10% of older Americans.
A recent review of the cognitive tests available for identifying impairment related to AD and its very early stages was conducted by researchers with the Minnesota Evidence-based Practice Center (EPC). This review applied a strict criteria to published studies claiming to provide evidence of the sensitivity and specificity of biomarkers and cognitive tests for changes that occur in AD. Their findings are published in an April 2020 Agency for Healthcare Research and Quality (AHRQ) Systematic Review, Diagnosis and Treatment of Clinical Alzheimer’s-Type Dementia.
Commenting on the import of the study, Dr. Howard Fink, the study lead and professor at the University of Minnesota and Director of the Minneapolis VA Geriatric Research Education and Clinical Center (GRECC), said, “More accurate diagnoses of the underlying causes of dementia in living patients could help patients and families better plan for what to expect in the future…More accurate identification of dementia type can help direct patients to research studies targeted at specific dementia types.”
In the analyses of cognitive assessments, the investigators reviewed research literature from studies that included brief cognitive tests administered in an outpatient setting via computer or pencil and paper formats. Researchers summarized evidence about these tests’ ability to identify Clinical Alzheimer’s-type Dementia (CATD) in individuals with suspected cognitive impairment.
The team found 56 studies that met their stringent inclusion criteria. The cognitive tests used in these studies included those designed as standalone measures of memory, language and executive function, as well as multidomain test batteries that examine several different cognition factors. Several of the cognitive tests were able to differentiate between moderate to advanced Alzheimer’s disease and normal cognition, while tests were less able to distinguish between mild Alzheimer’s and mild cognitive impairment (MCI) or between MCI and normal cognition.
The Cogstate Brief Battery (CBB) and the Cogstate International Shopping List Test were featured in the review. Results from the research rank both tests in the highest bracket for sensitivity and specificity at distinguishing CATD from normal cognition. The CBB was the only computerized cognitive test battery with published evidence sufficient to be included in the review. This requirement was that sample sizes were large, replication had occurred, and there was a low risk of bias in the results.
Summarizing the benefits of cognitive testing to identify CATD, Fink et al wrote that while these assessments on their own cannot diagnose Alzheimer’s, the cognitive tests they identified “may help providers decide which patients warrant a more comprehensive diagnostic evaluation. Brief cognitive tests may also provide a less burdensome way than comprehensive neuropsychological testing to objectively document cognitive impairment when patients have already undergone an appropriate cognitive history and have evidence of functional impairment.”