Sometimes doctors have a hard time determining whether cognitive symptoms are caused by clinical depression or by a neurological disease like dementia. Here's why the two conditions have so much overlap — and how to treat them both.
Depression is a common mood disorder that can make people feel persistently sad or hopeless, extremely fatigued, and cause them to lose joy in everyday activities they once found exciting. It can also have an impact on cognitive function. In fact, as many as three in five people diagnosed with depression will also experience memory loss or other problems with learning new information, remembering things, or staying focused.
People with these additional depression symptoms will have problems remembering directions, putting names to new faces, and carrying out more complex tasks which involve some planning.
That sounds a bit like the early stages of dementia, doesn’t it?
Unsurprisingly, many people with depression are mistakenly diagnosed with dementia — and on the flip side, many people living with dementia are also mistakenly diagnosed with depression. But it’s not uncommon for these conditions to co-exist either. More than 60 percent of people with dementia are also diagnosed with depression.
What do depression and dementia have in common?
There’s a lot of overlap in the symptoms between these two conditions, and some studies indicate that depression could even speed up the brain’s aging. Scientists and clinicians believe understanding this dementia-depression link could help treat both diseases.
Around 6.7 million Americans are living with Alzheimer’s disease or other forms of dementia according to a 2023 report from the Alzheimer’s Association. Meanwhile, according to a 2020 report by the U.S. Centers for Disease Control and Prevention, 18.4% of U.S. adults — nearly one in five — said they’ve been diagnosed with depression at some point.
Since both diseases occur so often, figuring out just how they’re related — and whether similar processes in the brain are driving them — is difficult. There are, however, many shared risk factors that provide scientists with clues.
There is even overlap in clinical trials, where researchers are looking at the effectiveness of depression treatments for some symptoms of dementia. A recent analysis found that the antidepressant drug fluoxetine may show promise in improving cognitive symptoms in Alzheimer’s.
And, both dementia and depression are treatable — but to varying extents.
Treating dementia and depression
One big difference between these two diseases is that depression is easier to treat.
Speaking with a doctor and getting the correct diagnosis is essential for treatment. Some older adults diagnosed with depression could experience more cognitive impairment when treated with some, but not all, antidepressants, while others could lower the risk of developing dementia.
On the other hand, there is currently only one fully FDA-approved disease-modifying treatment approved for Alzheimer’s — Biogen and Eisai’s drug Leqembi — but clinicians can only prescribe it to people in the very earliest stages of this one specific form of dementia.
Because they are each growing more prevalent, depression and dementia may be two of the most challenging medical issues that we face in the coming decades. However, learning what these two diseases have in common could help us treat both.