Last month, 75-year-old Martha K turned up at her friend's
house ex-pecting to find their bi-weekly book club in
progress, only to find that she had mistaken the day —
again. Are Martha's mix-ups merely part of the aging process
or are they a sinister sign of early stage Alzheimer's
disease (AD)? The key to answering this question may lie
in a report in the March 29 edition of the Proceedings
of the National Academy of Sciences (PNAS), which
describes a modification of a standard test for cognitive
impairment that more accurately pinpoints early AD.
"Early detection is absolutely
critical," stresses lead author Dr William Shankle,
of the University of California, Irvine, in an interview
with Reuters Health. This is because the damage done
by AD is irreversible and current treatments can slow
down deterioration.
OLD
TEST, NEW TRICKS
The standard scoring test for dementia is a mouthful
known as "the National Institute of Aging's Consortium
to Establish a Registry for Alzheimer's Disease's 10-word
list" (CWL). The test requires participants to recall
a 10-item word list three times immediately after looking
at it, and once after a time delay accomplished by having
the participant perform an interference task.
According to Dr Shankle, "[In]
the traditional scoring and intervention only the total
score from the fourth trial is usually used." But analysis
of the patterns of the words that are recalled can be
a goldmine of information. "The method we describe ...
uses the individual responses to every item in all four
trials to come up with an answer," adds Dr Shankle.
Answers to the modified 10-minute
test are analyzed using an algorithm that takes into
account the pattern of responses. The resulting correspondence
analysis (CA) — a technique that creates weighted
scores from individual performance profiles — is
pumped out in seconds. The PNAS paper compared
the modified test to the standard CWL test in 471 people,
who'd been previously evaluated using the interview-based
Clinical Dementia Rating Scale to confirm their status.
The CA-weighted scoring teased
out cases of true mild cognitive impairment from the
normal mental wear and tear of aging with a sensitivity
of 94%. In contrast, the CWL score had a sensitivity
of only 82%.
The modified test's sensitivity
— highest of any published test results to date,
according to the PNAS paper — may help physicians
get a jump on treatment. With such early treatment,
"many patients can live out the rest of their life with
no impairment or only minimal impairment," says Dr Shankle
in the paper.
PNAS Mar 29, 2005;102:4919-24
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