Practice imperfect—repeated cognitive testing can obscure early signs of dementia

July 12, 2018, University of California - San Diego
Credit: CC0 Public Domain

Alzheimer's disease (AD) is a progressive, neurodegenerative condition that often begins with mild cognitive impairment or MCI, making early and repeated assessments of cognitive change crucial to diagnosis and treatment.

But in a paper published online in the journal Alzheimer's & Dementia: Diagnosis, Assessment & Disease Monitoring, a team of researchers led by scientists at the University of California San Diego School of Medicine found that repeated testing of middle-age men produced a "practice effect" which obscured true cognitive decline and delayed detection of MCI.

"When persons take the same or similar tests repeatedly over time, they simply get better at taking the tests," said first author Jeremy A. Elman, Ph.D., a postdoctoral fellow in the lab of senior author William S. Kremen, Ph.D., professor of psychiatry and co-director with Carol E. Franz, Ph.D., of the Center for Behavior Genetics of Aging at UC San Diego School of Medicine. "The consequence is that their results may not accurately reflect the reality of their condition."

Researchers re-tested 995 middle- to late-middle-aged men in a six-year follow-up of the Vietnam Era Twin Study of Aging (a longitudinal study of male-male twins who had all served in the military sometime between 1965 and 1975, though almost 80 percent reported no combat exposure). A second group of 170 age-matched males were tested for the first time. Group differences were used to calculate practice effects.

The scientists found that there were significant practice effects in most cognitive domains, and diagnoses of MCI doubled from 4.5 to 9 percent after correcting for practice effects. "In other words," said Kremen, "some men would have declined to levels indicating impairment on follow-up testing had they not been exposed to the tests before."

The authors said the disparity has significant clinical consequences. Consider, for example, two people with similar characteristics who have identical cognitive scores just above the threshold for an MCI diagnosis. The only difference: One individual is being tested for the first time while the other has taken such tests before.

"We can infer that the second individual may actually have more impairment, but the effects of practice are artificially increasing their scores," wrote the authors. "This scenario would suggest that the individual may have dipped below the norm-based threshold and would have been diagnosed as having MCI had the test been taken for the first time."

The clinical significance, they said, is that treatment for AD is shifting increasingly toward prevention strategies that rely on early identification. The researchers say their findings strongly suggest the importance of correcting for effects in longitudinal studies of older adults, such as using similar replacement persons taking the test for the first time.

Explore further: Polygenic risk score may identify alzheimer's risk in younger populations

More information: Jeremy A. Elman et al, Underdiagnosis of mild cognitive impairment: A consequence of ignoring practice effects, Alzheimer's & Dementia: Diagnosis, Assessment & Disease Monitoring (2018). DOI: 10.1016/j.dadm.2018.04.003

Related Stories

Polygenic risk score may identify alzheimer's risk in younger populations

March 5, 2018
For the first time, an international team of scientists, led by researchers at University of California San Diego School of Medicine, have determined that an Alzheimer's disease (AD) polygenic risk score can be used to correctly ...

Diagnosis of Alzheimer's becoming more common, but less severe

June 26, 2018
Alzheimer's disease is the most common form of dementia, affecting nearly six million Americans. Aside from the incredible toll it takes on patients and their families, the estimated total cost of care is over $400 billion. ...

Late, but not too late—screening for olfactory dysfunction

April 20, 2018
In a large population-based study of randomly selected participants in Germany, researchers found that participants aged 65-74 years with olfactory dysfunction showed impaired cognitive performance. Interestingly, this strong ...

The role of verb fluency in the detection of early cognitive impairment in Alzheimer's disease

March 16, 2018
The ability to generate spoken verbs in infinitive in a given time begins to worsen in the early stages of Alzheimer's disease (AD). Thus, the verb fluency test has been found to be a suitable neuropsychological tool for ...

What if you could know that your mild cognitive impairment wouldn't progress

April 24, 2018
Researchers from the Lisbon School of Medicine, University of Lisbon found that, in some mild cognitive impairment patients, real neuropsychological stability over a decade is possible and that long-term stability could be ...

Alzheimer's drug prescribed 'off-label' for mild cognitive impairment could pose risk for some

February 24, 2017
Donepezil, a medication that is approved to treat people with Alzheimer's disease, should not be prescribed for people with mild cognitive impairment without a genetic test. UCLA School of Nursing researchers discovered that ...

Recommended for you

Study clarifies ApoE4's role in dementia

September 20, 2018
ApoE4, a protein linked to both Alzheimer's disease and a form of dementia caused by damage of blood vessels in the brain, increases the risk of cognitive impairment by reducing the number and responsiveness of blood vessels ...

Machine learning IDs markers to help predict Alzheimer's

September 19, 2018
Nearly 50 million people worldwide have Alzheimer's disease or another form of dementia. These irreversible brain disorders slowly cause memory loss and destroy thinking skills, eventually to such an extent that self-care ...

Discovery could explain failed clinical trials for Alzheimer's, and provide a solution

September 19, 2018
Researchers at King's College London have discovered a vicious feedback loop underlying brain degeneration in Alzheimer's disease which may explain why so many drug trials have failed. The study also identifies a clinically ...

Air pollution may be linked to heightened dementia risk

September 18, 2018
Air pollution may be linked to a heightened risk of developing dementia, finds a London-based observational study, published in the online journal BMJ Open. The associations found couldn't be explained by factors known to ...

A new approach for finding Alzheimer's treatments

September 11, 2018
Considering what little progress has been made finding drugs to treat Alzheimer's disease, Maikel Rheinstädter decided to come at the problem from a totally different angle—perhaps the solution lay not with the peptide ...

Study prevents cognitive decline in older blacks with memory loss

September 10, 2018
With nearly twice the rate of dementia as whites, blacks are at a higher risk for developing diseases like Alzheimer's, but there has been little research on how to reduce this racial health disparity. A new study in black ...

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.