Scientists continue to make advances in the diagnosis of Alzheimer's, using advanced brain scans and special dyes to detect the ways that the disease damages the brain. The advances could lead to earlier and more reliable diagnosis of Alzheimer's and help doctors develop more effective treatments for the disease.
Two new studies in the Archives of Neurology, a journal from the American Medical Association, describe how doctors are using positron emission tomography, or PET, scans to image the brain. The technique involves injecting radioactive dyes, or tracers, into the blood, which then permeate the brain. The special PET scanners then provide images of brain areas affected by beta-amyloid, a toxic protein that congregates in the brains of those with Alzheimer's.
In one of the studies, researchers from the Penn Memory Center in Philadelphia evaluated a tracer called fluorine 18-labeled flutemetamol. Seven volunteers suspected of having Alzheimer's were given the substance, then given PET scans. Following the PET scans they were given biopsies, which removed small samples of tissue from the brain to look for beta-amyloid, a toxic protein that builds up in the brains of those with Alzheimer's. The scans were accurate in visualizing areas of the brain affected by beta-amyloid and agreed with the results of the biopsies.
In the other study, researchers at Banner Alzheimer’s Institute in Phoenix used another dye called florbetapir F 18, followed by PET imaging. This study was larger, and included 68 individuals with probable Alzheimer's; 60 with mild cognitive impairment, a serious form of memory loss that sometimes precedes Alzheimer's; and 82 healthy individuals who served as controls. The three groups had distinct patterns of uptake of florbetapir F 18 in the brain, reflecting different levels of beta-amyloid buildup between those with Alzheimer's and the healthy controls.
Currently, doctors commonly use a dye called Pittsburgh compound B, which has been available for a number of years, to image brain changes with PET scans. These new dyes offer new and possibly more specific ways to monitor the progression of Alzheimer's disease and mild cognitive impairment. Because these newer dyes are more stable than Pittsburgh compound B, it may be easier one day to use them in doctor's offices.
“With the potential emergence of disease-specific interventions for Alzheimer's disease,” said Dr. David A. Wolk, one of the authors of the Penn report, “biomarkers that provide molecular specificity will likely become of greater importance in the differential diagnosis of cognitive impairment in older adults.” Earlier and more accurate diagnosis could be useful for testing new drugs to see whether they are effective in preventing disease progression.
Tests to measure levels of the toxic protein beta-amyloid, either in the brain or in the spinal fluid, have an increasingly important role in diagnosis of the disease.
In an editorial accompanying the papers, Dr. William J. Jagust of the Helen Wills Neuroscience Institute at the University of California, Berkeley, notes that this ongoing area of research is “a topic of active investigation” and “continues to advance the field.” Such testing may help to standardize results, so that early Alzheimer's might be diagnosed more reliably.
The findings also highlight the importance of basic research into the underlying causes of Alzheimer's disease. Only through continued research can doctors continue to make strides in diagnosis and treatment and, one day, find a cure for the disease.
Adam S. Fleisher; Kewei Chen; Xiaofen Liu; et al: Using Positron Emission Tomography and Florbetapir F 18 to Image Cortical Amyloid in Patients With Mild Cognitive Impairment or Dementia Due to Alzheimer Disease. Archives of Neurology, online, July 13, 2011. doi:10.1001/archneurol.2011.15
David A. Wolk; Igor D. Grachev; Chris Buckley; et al: Association Between In Vivo Fluorine 18–Labeled Flutemetamol Amyloid Positron Emission Tomography Imaging and In Vivo Cerebral Cortical Histopathology. Archives of Neurology, online, July 13, 2011, doi:10.1001/archneurol.2011.153
William J. Jagust: Amyloid Imaging: Liberal or Conservative? Let the Data Decide (editorial). Archives of Neurology, online, July 13, 2011. doi:10.1001/archneurol.2011.152