Sci. Aging Knowl. Environ., 28 January 2004
When Spacing Out Brings Clarity
Mental lapses serve as diagnostic clue for type of dementia
Rabiya S. Tumahttp://sageke.sciencemag.org/cgi/content/full/2004/4/nf11
NEW YORK CITY--Everyone has slow-witted moments: entering a room only to forget why, putting ice cream into the fridge, or blanking out on how to use the microwave. Some clinicians think that periodic mental lapses might help diagnose dementia with Lewy bodies (DLB), a scourge that kills brain cells (see DLB Case Study), although not all experts agree. Now, scientists have found that some cognitive blunders crop up more frequently in patients with DLB than in those with Alzheimer's disease (AD) or in healthy elderly individuals, according to work presented here on 15 January 2004 at an American Medical Association briefing for media.
Distinguishing between these two dementias is crucial because some of the drugs used to treat psychosis in AD exacerbate the symptoms of DLB. Clinicians concur that AD and DLB patients behave differently. For example, people with DLB frequently experience visual hallucinations and the rigidity and freezing that is typical of Parkinson's disease, whereas AD patients don't. Not every DLB patient suffers from the symptoms, however, so physicians can't rely on one feature for diagnosis. Many experts have suspected that cognitive fluctuations--periodic mental slowdowns--distinguish the disorder. But everyone experiences slow days, says Tanis Ferman, a neuropsychologist at the Mayo Clinic in Jacksonville, Florida, so using this trait for diagnosis has been controversial, especially because no reliable test for the fluctuations existed.
To address this problem, Ferman and her colleagues developed a questionnaire with which to gauge individuals' behavior, based on their own or a caretaker's responses. They gave it to 200 healthy adults, 70 AD patients, and 70 patients who appeared to have DLB based on symptoms of dementia plus hallucinations and/or the characteristic movement problems. Unlike previous tests for DLB, the 19-item questionnaire does not depend on the clinician's interview skills; it's a multiple-choice test. Sixty-three percent of the DLB patients had at least three symptoms associated with cognitive fluctuations, whereas only 12% of the AD patients and 0.5% of the normal elderly volunteers did. Four symptoms are crucial for distinguishing the disorders, the researchers found: more than 2 hours of daytime sleeping, excessive lethargy, staring into space for a long time, and periods of incoherent speech. The test can differentiate DLB from AD 83% of the time. "This gives us a clear set of behaviors to use to reliably distinguish the fluctuations of Lewy body dementia from Alzheimer's," says Ferman.
The test also allowed the researchers to discriminate between normal aging and disease-related declines. Although 88% of the mentally healthy participants showed none of the four symptoms, 12% had one or two (see "When Does Normal Aging Become Abnormal?")--and among them, unlike DLB and AD patients, the likelihood of experiencing cognitive fluctuations rose with increasing age.
"We cannot treat patients until we have a diagnosis," which makes this finding important, says Marcelle Morrison-Bogorad, a neurobiologist at the National Institute on Aging in Bethesda, Maryland. The new questionnaire could simplify one of neurologists' significant challenges--making it almost as straightforward as using a microwave.
January 28, 2004
Science of Aging Knowledge Environment. ISSN 1539-6150