There's no single test that can differentiate depression from dementia. But some behavior clues may help the doctor make an educated assessment.
"Alzheimer's disease and depression are probably related in ways we don't understand," says Brent Forester, MD, director of the mood disorders divison in the geriatric psychiatry research program at McLean Hospital in Belmont, Mass. "Forty to 50% of people with Alzheimer's disease get depression, but depression also may be a risk factor for Alzheimer's."
Here is how geriatric psychiatrists tell the two conditions apart.
- Memory: People who are depressed may have trouble concentrating. They may even suffer occasional memory lapses, which can make their mood worse. But people with Alzheimer's disease consistently have trouble storing new information, such as the recent visit of a close relative or what they ate for dinner. They may not remember eating dinner at all.
- Orientation: Most people who are depressed generally know with whom they're speaking, what time and day it is, and where they are. People with dementia tend to be confused about some or all of this.
- Language use: Depressed people use language properly, although they may speak slowly at times. People who are demented because of Alzheimer's disease or strokes often have lots of language problems. Particularly hard: remembering the names of common objects such as "pen" or "lamp" or "birthday cake."
- Use of familiar objects: Again, not a problem for people with depression. Someone with dementia may not recall how to get a pullover sweater on, for example. This is called apraxiatrouble remembering how to perform previously learned and routine motor activities.
- Negativity: Depressed people have a general tendency to put a negative spin on events. For example, if asked to take a test designed to screen for depression or Alzheimer's, they may jump to the conclusion that they did quite badly, and they often overestimate the problem. In contrast, someone with dementia may try to fabricate some story or excuse for a memory lapse or poor performance on a memory test.