Monday November 9 2009
“A multi-tasking test can help avoid confusion between symptoms of depression and early Alzheimer’s,” The Daily Telegraph reported. It said that people with Alzheimer’s often have mildly impaired reasoning and memory, which can easily be mistaken for signs of depression. This can lead to them being wrongly diagnosed.
This news is based on research that involved a ‘dual test’, in which two different mental tasks were carried out simultaneously. It found that Alzheimer’s patients performed worse than people with depression and healthy people.
To see whether a test based on this principle improves the overall diagnosis of Alzheimer’s, it will need to be tested alongside the usual assessments in a larger group of patients who are not already known to have Alzheimer’s disease.
Where did the story come from?
The research was carried out by Dr Reiner Kaschel and colleagues from the University of Osnabruck in Germany. The source of funding for the research is not clear. The study was published in the peer-reviewed medical journal Journal of Neurology.
Generally, the study was reported accurately in the newspapers.
What kind of research was this?
The researchers say that, when making a clinical diagnosis, it is difficult to distinguish between early Alzheimer’s disease and chronic depression in the elderly. This cross-sectional study compared the performance of Alzheimer’s patients to people with chronic depression and a group of healthy individuals in a dual task. The purpose was to determine whether performance in this kind of task is different between the groups and, therefore, potentially discriminatory, that is whether it could tell people with Alzheimer’s apart from healthy people or those with depression.
This was not a usual diagnostic study, in which a test’s ability to identify people with Alzheimer’s (to help diagnose the disorder) is assessed in a group of people who are not already known to have Alzheimer's (an unselected population). The participants in this study were known to have Alzheimer’s disease and were compared with people known to have depression.
What did the research involve?
The researchers carried out two separate experiments to validate their test. In the first, 22 patients with Alzheimer’s disease were recruited from a memory clinic. The patients were diagnosed using conventional methods and none of them had a history of other neurological or psychiatric disorders, or alcohol or drug abuse. A test for depression in this group showed that none of them had depression.
The researchers also recruited 43 people with chronic depression (who had not had a period of remission for longer than one month at a time) who did not have neurological or psychiatric disorders and did not abuse alcohol and drugs. This group did not have signs of dementia.
As a control group, 24 healthy people were also tested. These were relatives or spouses of people in the other groups and had no current or previous neurological or psychiatric disorders.
Each group performed memory tests, specifically of their episodic memory (the ability to recall times, places and past experiences). All participants were then given the dual task assessment, in which they simultaneously carried out a digit recall test and a tracking task. The digit recall test involved repeating a sequence of numbers read aloud by an experimenter. The tracking task involved drawing a line through a series of circles arranged irregularly on a sheet of paper. These tasks were also performed separately.
Each group’s performance on the dual task and the separate tasks were then compared. The researchers found that Alzheimer’s patients had worse episodic memory than the other groups. To take into account the possibility that performance on the dual test was affected by differences in the individuals’ episodic memory, this was adjusted for in the analyses. The researchers then used a formula to calculate the difficulty of carrying out both tasks simultaneously and of carrying them out consecutively for the two groups.
The second experiment was similar and included 29 new Alzheimer’s patients and 24 new depressed patients. The difference between this and the first experiment was that the people with depression also had episodic memory problems. The results were analysed in the same way as above.
What were the basic results?
In the first experiment, all three groups performed equally well in the digit recall test and the tracking task when they were carried out separately. On the dual test, people with Alzheimer’s disease performed worse on tracking compared with both the control group and the depressed group. People with depression did not differ from the control group. The three groups performed as well as each other in the digit recall test when the tests were carried out simultaneously.
In the second experiment, the Alzheimer’s patients performed worse than the depressed group on both digit recall and tracking tasks when the tests were carried out simultaneously. There was no difference in performance when the tasks were given separately.
How did the researchers interpret the results?
The researchers say that the function required to perform concurrent memory and tracking tasks is affected in people with Alzheimer’s disease, compared to healthy controls and to people with depression, and this is independent from memory differences between the groups.
The results of the second experiment in which Alzheimer’s patients and depressed patients were balanced (i.e. both people with depression and those with Alzheimer’s had episodic memory problems) confirm this.
This series of cross-sectional observations has demonstrated that Alzheimer’s patients perform worse than healthy elderly people and those with depression in this dual task. This seems to be independent from the memory problems commonly associated with Alzheimer’s.
The results are important in the field of neurology because they further the understanding of the effect of Alzheimer’s on the brain. As the researchers say, these results and those of other studies support the idea that Alzheimer’s affects the brain function that allows tasks to be performed simultaneously.
Importantly, this study does not offer "a new test" for Alzheimer’s disease, but demonstrates that people with Alzheimer’s may have specific problems co-ordinating two simultaneous tasks. A potential value of adding this test to existing tests is that it might improve the specificity of these tests (the ability of the test to correctly identify people who do not have the disease).
To establish whether a dual task test would improve overall diagnosis of Alzheimer’s, it would need to be added to the usual assessments to see whether it correctly identifies the disease in a larger, unselected group of people, and the results compared to the gold standard diagnostic tools for the disease.