Oct. 12 (HealthDay News) -- The ability to perceive relationships between objects (visuospatial skills) may decline years before a person is diagnosed with Alzheimer's disease, a new study suggests.

It included 444 people who were dementia-free when they were enrolled in the study and underwent tests on a number of cognitive abilities, including visuospatial skills. The assessments were repeated at least once before the end of the study. After an average follow-up of 5.9 years, 134 participants had developed dementia. Of those, 44 underwent brain autopsies that confirmed they had Alzheimer's disease.

The researchers used data from the cognitive assessments to chart declines in various areas before participants were diagnosed with dementia. They found an inflection point (sudden change to a steeper slope of decline) in visuospatial abilities three years before clinical diagnosis of dementia.

Declines in overall cognition occurred the next year, while inflection points for verbal and working memory weren't seen until one year before diagnosis.

The findings appear in the October issue of the Archives of Neurology.

"There are several implications of this study," wrote David K. Johnson, of the University of Kansas, and colleagues. "Some of the earliest signs of preclinical disease may occur on tests of visuospatial and speeded psychomotor skills. Furthermore, the greatest rate of preclinical decline may occur on executive and attention tasks. These findings suggest that research into early detection of cognitive disorders using only episodic memory tasks, such as word lists or paragraph recall, may not be sensitive to either all of the earliest manifestations of disease or the most rapidly changing domain."

"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."

SOURCE: JAMA/Archives journals, news release, Oct. 12, 2009