A new study from a center for Alzheimer’s research in the US suggests that cognitive skills other than memory, for example visuospatial skills that help us work out how objects relate to each other in three dimensions as we look at them, start to decline years before patients receive a clinical diagnosis for Alzheimer’s.
The study was the work of Dr David K Johnson, of the University of Kansas, Lawrence, and colleagues, and is published in the October issue of Archives of Neurology, one of the JAMA/Archives journals.
The authors wrote that more and more researchers are now looking at when healthy aging turns into the early stages of dementia.
“As new interventions become available, it will become important to identify the disease as early as possible,” they explained.
Loss of episodic memory, that part of memory that is like an autobiography, where one can explicity recount the times and places of particular events and the emotions we felt, is commonly linked to Alzheimer’s, but it is not the only part of cognition (thinking, learning and memory) that is affected by the disease.
For the longitudinal study, Johnson and colleagues followed 444 people who did not have dementia when they enrolled between 1979 and 2006.
Upon enrolling, each participant underwent a clinical evaluation that also tested four cognitive factors: global cognition, verbal memory, visuospatial skill and working memory. They did the tests at least one more time before the end of the study in November 2007.
The average follow up was 5.9 years, during which 134 of the participants developed dementia, and 310 did not. 44 of those with dementia died and when their brains were examined post mortem they showed signs that confirmed a diagnosis of Alzheimer’s.
Brains of people who die with Alzheimer’s disease contain abnormal amounts of amyloid plaques and neurofibrillary tangles that can be seen under a microscope.
When they modelled the results of the cognitive assessments in line with the timing of the clinical diagnoses for dementia, the researchers found that the results for visualspatial skills showed a sudden change to a steeper slope of decline (an “inflection point”), three years before clinical diagnosis.
After that followed decline in overall cognitive ability, which suddenly declined more steeply two years before diagnosis, with verbal and working memory doing the same one year before diagnosis.
When they looked at other subgroups of the dementia patients, the only subgroup to show a similar pattern of decline with the same inflection points was the subgroup of participants with Alzheimer’s disease whose diagnosis was confirmed by autopsy.
The authors concluded that:
“Research into early detection of cognitive disorders using only episodic memory tasks may not be sensitive to all of the early manifestations of disease.”
“In summary, converging longitudinal evidence suggests that after a sharp departure from the relatively flat course of normal aging there is a preclinical period in Alzheimer’s disease with insufficient cognitive decline to warrant clinical diagnosis using conventional criteria but that can be seen with longitudinal data from multiple domains of cognition and not just memory,” they added.
The study was supported by grants from the National Institute on Aging, part of the National Institutes of Health.
“Longitudinal Study of the Transition From Healthy Aging to Alzheimer Disease.”
David K. Johnson; Martha Storandt; John C. Morris; James E. Galvin.
Source: JAMA/Archives.
Written by: Catharine Paddock, PhD