Psychologists say that after examining dozens of Alzheimer's studies, they now have a clear picture of the cognitive problems which will develop in people with the degenerative brain disease.
Apparently this comprehensive analysis reveals that people can show early warning signs across several cognitive domains, years before they are officially diagnosed.
This finding confirms that Alzheimer’s causes general deterioration and follows a stable preclinical stage with a sharp drop in function.
Ten years worth of studies were examined by researchers at the Karolinska Institute and Stockholm Gerontology Research Center; they were affiliated with the Max Planck Institute for Human Development and the University of South Florida.
The reports examined, had already met stringent criteria and had records on 1,207 people with preclinical Alzheimer’s, who later developed the disease, and 9,097 controls who stayed healthy.
There are two reasons why neuropsychologists are eager to understand the preclinical stage; understanding the transition from normal aging to dementia is vital in understanding how the disease evolves, and, if doctors can identify at-risk individuals as soon as possible, treatment can be more effective.
In their research the authors studied 47 peer-reviewed studies published between January 1985 and February 2003; 1985 marks the introduction of more systematic and reliable diagnostic criteria for Alzheimer’s.
Their analysis showed that in all the studies, people at the preclinical stage exhibited marked preclinical deficits in global cognitive ability, episodic memory, perceptual speed, and executive functioning; along with somewhat smaller deficits in verbal ability, visuospatial skill, and attention. There was no preclinical impairment in primary memory.
According to the authors, the generalized nature of the problem is consistent with recent observations that multiple brain structures and functions are affected long before the AD diagnosis.
They do point out however that the deficits seen in preclinical AD mirrors quite closely those seen in normal aging, such as impairments in episodic memory, executive functioning, and cognitive speed.
Lead author Lars Backman, PhD, says though, that these problems are exacerbated in those who will go on to be diagnosed with dementia.
He says, that as there are no clear qualitative differences in patterns of cognitive impairment, between the normal old 75-year old, and the preclinical AD counterpart, this presents an obvious challenge for accurate early diagnosis.
Also supported in the research is 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 plummets.
A multi-variable approach to understanding the preclinical stage of AD, will help clinicians to more accurately predict the likelihood of disease, and is encouraged by Backman and his colleagues.
Other interesting patterns were revealed in the study.
It was found that people younger than 75 years at baseline were more impaired at the outset than people older than 75 at baseline.
Impairment was also greater for the patients with shorter periods (fewer than three years) to diagnosis.
These findings suggest that preclinical impairment is greater when the disease starts younger and progresses more quickly, due to more widespread and severe brain lesions among younger cases.
The findings appear in the July issue of Neuropsychology, which is published by the American Psychological Association.