Is it Dementia, Depression or Both?

From Jan. 30–Feb. 2, ASA presents the Generations Forum Mental Health & Aging. While planning the Forum the idea was raised that people may have a difficult time differentiating between dementia and depression when it occurs in older adults. This post details those differences.

Dementia and depression both can be common after age 65. Also, they both impair functional abilities in older adults, albeit in different ways. Still, to an untrained observer, the two conditions may be difficult to differentiate. Occasionally, even experts find the distinction challenging. Because the two disorders can overlap by chance and because there is more than a chance of co-occurrence between the two disorders, it is best to approach them separately.

Is it Dementia?

In people older than age 65, the prevalence of dementia is so strongly related to age that up to half of people ages 90 and older are affected. Dementia refers to a loss of cognitive abilities relative to a younger age. By definition the decline in cognitive abilities needs to be sufficiently severe as to impair usual daily function. Dementia is not subtle. Yet, function is often limited by other physical conditions. Thus, classic signs of dementia can be missed in someone who is also limited by physical disabilities, which are common in older persons.

Repeating questions and getting lost are among the hallmark early signs of dementia. However, because memories from youth and middle age are retained early in dementing illnesses, observers may conclude that the memory is fine. Other things that may be noticed are withdrawal from usual hobbies and friends, and disengagement in conversation. This can be interpreted as depression. But loss of memory and cognition impair social interactions as well because social interactions require retaining information for an extended period of time, a duration that often exceeds the memory capacity of an affected person.

Dementia is caused by one or more neurologic diseases of the brain. These diseases fall into two groups. One is neurodegenerative diseases. Here, the brain is physically smaller due to destruction of brain tissue. These diseases have characteristic pathologies that can be seen under a microscope. The most common neurodegenerative disease is Alzheimer’s disease with its characteristic neuritic plaques and neurofibrillary tangles. Neurodegenerative diseases cause progressive dementia that relentlessly worsens over time.

People who are depressed also disengage socially and thus share some of the signs that are seen with dementia.

The second group are cerebrovascular diseases that typically exist in the absence of an actual stroke. These also can be seen upon inspection of the brain and in some cases with a brain MRI scan. Like neurodegenerative diseases, these, too, most commonly cause a progressive dementia. In essence, being able to visualize the abnormality in the brain on a person-specific basis is what makes these conditions neurologic. These diseases are all related to age in that the most common cause of dementia in old age is Alzheimer's disease with one, two, three or more other conditions. It’s increasingly important to be able to determine whether someone has Alzheimer's disease given recent progress in both biomarkers such as PET scans, spinal fluid and more recently blood tests, for the disease and therapeutics that target the underlying disease pathology.

What Is Depression?

In contrast to dementia, major (unipolar or bipolar) depression peaks at younger ages and is sufficiently distinct such that it does not, except in quite unusual cases, present a diagnostic conundrum. But old age is often accompanied by Persistent Depressive Disorder or Dysthymia. Depression has no obvious abnormality on a brain scan or under a microscope or on any other test that is now performed. It is a psychiatric disease. The central hallmark of depression is persistent depressed mood, persistent sadness.

Older persons are susceptible to depression for many reasons such as the death of a spouse, sibling or close friends. Physical disabilities and loss of social connections can result in house-bound, lonely older persons. About five years ago the United Kingdom appointed a Minister of Loneliness to make policy recommendations to combat this common problem. People who are depressed also disengage socially and thus share some of the signs that are seen with dementia. In contrast to dementia, depression is not relentlessly progressive. It tends to fluctuate over time and situational depression, e.g., loss of a family member or close friend, typically improves over time. Making a diagnosis of depression is important as there are medications that can improve mood and function.

Is it Both?

While two common conditions such as dementia and depression will co-occur by chance, there is now very good evidence that depressive symptoms are a risk factor for dementia. Thus, the two conditions co-occur more often than just by chance. For example, in a recent study we reported that persons with modest depressive symptoms developed Alzheimer’s dementia an average of five years sooner when compared to persons without depressive symptoms. Further, it has long been known that dementia can result in depression.

Both dementia and depression are diseases of the brain. But they are very different diseases. The former results in brain degeneration and the accumulation of characteristic pathologies that are progressive and track with loss of cognition and function. The latter has no obvious visual pathologies and fluctuates or improves. While they can mimic one another, a careful history and examination can usually identify whether it’s one, the other, or both. Also, there are therapeutic strategies for both that warrant all professionals and non-professionals who work with older persons to be vigilant for their signs and to be familiar with their differences.

David Bennett, MD, directs the Rush Alzheimer’s Disease Center and is the Robert C. Borwell Professor of Neurologic Sciences at Rush University Medical Center, in Chicago, IL.