August 2005
It's important to be able to predict who will develop Alzheimer's Disease (AD) and related dementias as soon as we possibly can. Identifying the "preclinical phase" of AD will help researchers develop medications that may forestall the dementia that is to develop later. It also helps families plan for the future.
A recent meta-analysis (where a number of past studies were considered together) reveals that people often show warning signs years before they are officially diagnosed with AD. This confirms the generally held view that Alzheimer’s causes general deterioration and usually follows a stable preclinical stage followed by a steeper drop in function.
The researchers in this study reviewed 47 peer-reviewed studies published between January 1985 and February 2003. They included only studies over the past 10 years that met stringent criteria. They reviewed data from 1,207 subjects diagnosed with preclinical Alzheimer’s who later actually developed AD. They also reviewed the data from 9,097 control subjects who did not develop AD.
Persons with "preclinical Alzheimers" showed:
- deficits in global cognitive ability (They were not thinking as well in general.)
- episodic memory problems (memory for specific events, dates, places)
- perceptual speed deficits (They were slower in sensing changes in their environment.)
- executive functioning deficits (They could not make decisions as well.)
- smaller deficits were seen in in verbal ability, visuospatial skill (tasks such as putting together puzzles), and attention
- no impairment in "primary memory" was seen in preclinical AD (suggesting that the patients scored as well as expected on tests of general memory)
The current meta-analysis also supported the emerging consensus that AD’s preclinical period is characterized by an early onset followed by relative stability until a few years before diagnosis, when functioning deteriorated rapidly.
Subjects younger than 75 years at baseline were more impaired at the outset than subjects older than 75 at baseline. Impairment was also greater for the patients with fewer than three years before they were diagnosed with AD. The authors conclude that preclinical impairment is greater when the disease starts younger and progresses more quickly, probably due to more widespread and severe brain lesions among younger cases.
Reference Lars Bäckman, PhD, Sari Jones, PhD, Anna-Karin Berger, PhD, Erika Jonsson Laukka. PhD, and Brent J. Small, PhD. Cognitive impairment in preclinical Alzheimer’s disease: A meta-analysis; University of South Florida. Neuropsychology, Vol. 19, No. 4.
Last updated 11/5/05
