Core idea

In this post, we report on a comprehensive review article (rather than an article on a single study) that pulled together literature on a very important topic: The search for early signs of dementia.

Traditionally Alzheimer’s disease has been diagnosed in individuals suffering from episodic memory loss (loss of memory for events); however, new research shows that there may be other cognitive deficits that may come before memory loss.  Diagnostic criteria need to be updated to include the following cognitive deficits when diagnosing elders in the early stages of Alzheimer’s disease: changes in personality, difficulty in executive function (difficulty in decision-making and planning), difficulties in attentional and inhibitory control, and deficits in semantic memory (deficits in the meaning of words). 

What they say

One reason it has been difficult to study psychological deficits that exist in Alzheimer’s before memory is affected is that memory loss is required for the diagnosis of Alzheimer’s. Therefore, only people with memory problems typically have been studied.  Thus the segment of the population without memory problems (but with other cognitive deficits that are precursors to Alzheimer’s) has not been studied widely.  

Recently there have been longitudinal studies (studies that are done over the span of several years) that examined people who at the start of the study did not have Alzheimer’s but eventually developed the disease.  One study found that verbal memory and an abstract reasoning test predicted Alzheimer’s.  Another study found that poor initial performance on measures of attention and executive function were better predictors of which individuals would develop Alzheimer’s.  A third study found that performance on a test that involved planning and sequencing predicted whether a person would be eventually diagnosed with Alzheimer’s.

In addition to longitudinal studies, other studies have looked at individuals who have experienced some decline but do not meet existing criteria for an Alzheimer’s diagnosis.  These individuals are said to experience mild cognitive impairment. Only 61% of those with mild cognitive impairments began with memory loss.  The initial problems for the remaining 39% were visuospatial (11%), executive function (19%), or combined visuospatial and executive deficits (9%).

Other studies found that early stages of Alzheimer’s could be predicted even before people experienced mild cognitive impairment -- by using information about changes in the person’s previous levels of functioning.  This information was obtained from other people who knew that person. One study found that in a sample of adults without dementia, about half of those who later developed dementia had experienced changes in personality. Other changes that were predictive of Alzheimer’s were increased rigidity, apathy, self-centeredness, and emotional lability. People without dementia but with reported personality change were twice as likely to be diagnosed with Alzheimer’s two years later.

What it means

Psychological functions other than memory appear to be affected quite some time before the diagnosis of Alzheimer’s. Changes in personality and higher-order cognitive functions such as reasoning and executive function can predict Alzheimer’s disease.

References

Storandt, M. (2008). “Cognitive Deficits in the Early Stages of Alzheimer’s Disease.” Current Directions in Psychological Science, 17(3), 198-201.