A recent study on AD has revealed that people who go on to have Alzheimer's disease (AD), lose several of their cognitive abilities much before they actually succumb to dementia caused by the neurodegenerative disorder.
Researchers at the University of Kansas, Lawrence, have said that in such people, declines of thinking and learning skills, including visuospatial skills needed to perceive relationships between objects, may decline years prior to a clinical diagnosis of AD.
"Recent studies have focused on identifying the beginning of the transition from healthy aging to dementia. As new interventions become available, it will become important to identify the disease as early as possible," wrote the authors of the study.
Loss of episodic memory-remembering events in one's life that can be explicitly stated-is commonly linked to Alzheimer's disease, but it is not the only aspect of cognition (thinking, learning and memory) that is affected.
Researchers led by Dr. David K. Johnson assessed 444 individuals who did not have dementia when they were enrolled in the study, between 1979 and 2006.
After enrolment, each participant underwent a clinical evaluation and a psychometric assessment including tests of four cognitive factors-global cognition, verbal memory, visuospatial skill and working memory.
Participants were then evaluated at least one additional time before November 2007.
Over an average follow-up of 5.9 years, 134 individuals developed dementia and 310 did not; 44 with dementia died and underwent brain autopsies that confirmed a diagnosis of Alzheimer's disease.
Using data from the psychometric assessments, the researchers constructed models to evaluate the decline in various cognitive areas before individuals were diagnosed with dementia.
"A novel finding was that visuospatial abilities demonstrated an inflection point [sudden change to a steeper slope of decline] three years before clinical diagnosis," wrote the authors.
Declines in overall cognitive abilities followed in the next year, whereas inflection points for verbal and working memory were not seen until one year before clinical diagnosis. Similar results occurred in only the subgroup of individuals with Alzheimer's disease diagnosis confirmed by autopsy.
The study has been published in the latest issue of Archives of Neurology, one of the JAMA/Archives journals.