Link Between Subjective And Objective Memory Decline

"Several studies have found that people with subjective cognitive decline have an increased risk of dementia," said study author Michael Wagner, PhD, of the German Center for Neurodegenerative Diseases in Bonn. "Our results now suggest that people with subjective cognitive decline who also have minor test deficits, or early signs of memory and thinking problems not yet reaching the diagnosis of mild cognitive impairment, may be more likely to progress to memory disorders. Testing for these deficits in people with self-reported decline could help identify people at a higher risk for progressing to mild cognitive impairment."

For this study, 439 participants with subjective cognitive decline and an average age of 71 years old without dementia or mild cognitive impairment completed a series of testing to assess thinking and memory skills. These tests included memorizing lists, copying a drawing, and identifying time frames and current location. For this study minor test deficits were defined as having a score of at least 0.5 standard deviations below average score. Mild cognitive impairment was diagnosed by a panel that reviewed participant performance across the tests, and a score of at least 1.5 standard deviations below the average was necessary for a diagnosis. 

According to the researchers, of those with subjective cognitive decline, 13% (55 people) had minor test deficits at the beginning of the study, and 87% (384 people) did not have minor deficits. Participants were followed for an average of 3 years to see who developed mild cognitive impairment. After adjusting for a variety of factors, those with subjective cognitive decline who also had minor test deficits were more than four times more likely to progress to mild cognitive impairment compared to those without minor deficits. 

Among those with subjective cognitive decline, 17% (58 people) who did not have minor deficits and 48% (24 people) who did have minor deficits progressed to mild cognitive impairment at follow-up. Those with subjective cognitive decline and minor test deficits had a 35% probability of developing mild cognitive impairment within 2 years and an estimated probability of 84% of developing mild cognitive impairment within four years. Those with subjective cognitive decline and minor test deficits were also found to have higher levels of biomarkers measuring protein changes in the brain, indicating an increased risk of Alzheimer’s disease. 

"Our results shed new light on the link between subjective and objective decline before being diagnosed with Alzheimer's dementia," said Wagner. "Future research may help doctors to measure and communicate individual risk for people with subjective cognitive decline."