September 20, 2003
Alzheimer's disease is often difficult to diagnose, especially early in the course of the illness, when memory lapses may be mild and symptoms may be mistaken for depression or other ailments that can impair mental focus. Researchers from the University of Zurich in Switzerland report on a new laboratory test that, if results are confirmed, may aid doctors in the diagnosis of Alzheimer's and help to distinguish it from other, potentially treatable, causes of dementia and memory loss. The study appeared in the September 15, 2003 issue of the Archives of Neurology, a medical journal for physicians.
The test measures two compounds in the spinal fluid, high levels of which have been linked to Alzheimer's disease. One of these, known as tau protein, is a key component of the twisted nerve cell fibers (neurofibrillary tangles) that accumulate in the brains of people with Alzheimer's. The other, a toxic substance called beta amyloid, is a sticky protein that builds up around dying nerve cells in Alzheimer's-addled brains.
The ratio of tau to beta amyloid was significantly higher in the spinal fluid of people with Alzheimer's, the researchers report, than in those who had other forms of dementia or nervous system disorders. It was also higher than the ratio in healthy controls who had no mental decline.
The scientists concluded that the spinal fluid test could offer "a promising tool" for diagnosing Alzheimer's at an early stage but called for additional testing to confirm the results and to determine when they may be most accurate. In the current report, the researchers took spinal fluid samples from 100 patients who entered a clinic with symptoms of Alzheimer's or other forms of dementia. They also tested 31 mentally alert men and women who served as comparison controls.
"These results need further, independent confirmation," reiterates Samuel Gandy, M.D., Ph.D., Chairman of the Scientific Advisory Board of the Fisher Center for Alzheimer's Research Foundation. "A recent review of the literature on these markers was less impressive than the claims made in the Archives of Neurology paper." That review, which analyzed earlier studies, appeared in the April 23-30, 2003 issue of the Journal of the American Medical Association.
Early Diagnosis: An Ongoing Dilemma
A prompt test to diagnose Alzheimer's would be extremely helpful for the care and management of patients with the disease. Detecting the disease earlier in its course may allow more patients to benefit from currently available Alzheimer's drugs because, although their benefits are limited these medicines are most effective for those with early-stage Alzheimer's. Prompt diagnosis would also allow patients and their loved ones better prepare for the future.
Researchers have been investigating sophisticated imaging techniques, such as MRI and PET scans, to look for changes in the brain's structure or areas of activation that may indicate a diagnosis of Alzheimer's. They have also been measuring proteins in the fluids that circulate in the brain and spinal cord to look for markers of Alzheimer's.
So far, however, no lab test can accurately diagnose Alzheimer's disease with a high degree of certainty. In some cases, the disease cannot be definitively diagnosed until an autopsy is done after death.
In an accompanying editorial, Douglas Galasko, M.D., of the University of California, San Diego, notes that dementia specialists can currently diagnose Alzheimer's disease about 90 percent of the time, but that general physicians are less successful at making a diagnosis.
Dr. Glasko likewise calls for additional research to confirm the accuracy of the current laboratory findings and to determine how they compare to typical symptom-based diagnoses based in a typical doctor's office.
"In view of the increasing emphasis on early detection," he writes, "patients with MCI, or mild cognitive impairment, should also be evaluated." MCI is a mild form of memory loss in older people that, in some cases, eventually progresses to Alzheimer's disease.
For more on the diagnosis of Alzheimer's disease, visit www.ALZinfo.org.
By Toby Bilanow, Medcial Writer, for www.ALZinfo.org, The Alzheimer's Information Site. Reviewed by Samuel E. Gandy, M.D., Ph.D., Chairman of the Scientific Advisory Board, Fisher Center for Alzheimer's Research Foundation.