Cognitive tests can identify mental decline, but they do not do a very good job of differentiating Alzheimer’s disease (AD) from vascular dementia, the American Psychological Association suggests.

A meta-analysis of 81 previous studies concludes that when older people are confused and forgetful, clinicians should base their diagnoses on many different types of information, including medical history and brain imaging, as well as testing.

While both AD and vascular dementia affect learning and memory, behavior, and day-to-day function, the two disorders have different causes that require different treatment. Consequently, it’s important to tell them apart accurately, the report emphasizes (Neuropsychology. 2009; 23:441-423).

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The meta-analysis compared the cognitive testing of people diagnosed with dementia of the Alzheimer’s (4,867) or vascular type (2,263). The average age of participants was 75 years.

Of the 118 tests used in more than one study, researchers found that only two were able to adequately differentiate between Alzheimer’s and vascular dementia: the Emotional Recognition Task and the Delayed Story Recall.

Nevertheless, the results were not definitive, and further diagnostic testing was needed. “The combined picture is what’s important, so we need to look at how we can improve diagnosis by combining different measures,” the authors say.

Many common tests (e.g., repeating a set of numbers forward and backward; listing words by a category, such as animals, or by first letter; and drawing) were unable to distinguish between dementia types. “While these tests may assist in diagnosing dementia, they do not adequately discriminate,” the authors write.

Teasing apart the different types of dementia is often harder than deciding whether someone has dementia in the first place.

“All cognitive tests were limited in their ability to discriminate between [AD] and vascular dementia, suggesting that [the tests] should be used cautiously and only in conjunction with other information (imaging, medical history) when diagnosing patients,” the authors conclude.