Depression may be an early sign of Alzheimer's disease

In the elderly, symptoms of depression such as low energy and concentration problems may be early signs of Alzheimer's disease, according to Swedish researchers.

The results of their study suggest that these symptoms are not due to patients realising that their memories are failing, but rather that depressive symptoms are part of the early stages of Alzheimer's.

In a 3-year study that followed 222 people aged 74 and older, researchers found that those who developed Alzheimer's were 50% more likely than other participants to have suffered depressive symptoms at the study's start.

"The people who developed Alzheimer's weren't even close to a clinical diagnosis of depression, but they did have more symptoms of depression, such as a lack of interest, loss of energy and difficulty concentrating," lead researcher Dr. Lars Backman said in a statement. Backman and his colleagues at the Stockholm Gerontology Research Centre report their findings in the December 10th issue of the journal Neurology.

Although other investigators have noted a link between depression and Alzheimer's, the nature of this relationship has been unclear. Some studies have suggested depression may be a risk factor for Alzheimer's; other researchers have concluded that Alzheimer's patients suffer depression as an emotional response to the loss of memory and thinking abilities that mark the disease.

This study, according to Backman's team, suggests that depression is neither a response to Alzheimer's nor a risk factor, but rather an early sign of the disease.

Backman and colleagues looked at two types of depression among the study participants -- "mood-related" symptoms such as unhappiness, guilt and thoughts of death; and "motivation-related" symptoms including lack of energy and interest, and concentration problems. They found that at the start of the study, participants who would later develop Alzheimer's commonly had motivation-related symptoms.

"That provides further evidence that the symptoms are not related to people's feelings about their cognitive difficulties, and actually reflect changes in the brain regions involved in attention and energy," Backman explained in the statement.

Alzheimer's currently affects about 4 million Americans; as the elderly population grows, that number is expected to jump to 14 million over the next 50 years, according to the Chicago-based Alzheimer's Association. There is no one test that diagnoses the brain disease. Rather, physicians rely on a combination of physical, psychological and neurological tests to diagnose "probable" Alzheimer's.

According to Backman, because the depressive symptoms that emerged in his study are fairly common among the elderly, they may be "easily overlooked" as early signs of Alzheimer's disease.