What Dementia, MCI, and Subjective Cognitive Decline Mean

Understand the terminology of memory disorders.

Posted February 23, 2019 | Reviewed by Davia Sills

Dementia means problems with thinking and memory are impairing daily function

When people have problems with their thinking and memory to the point that they can no longer function independently, they have dementia . People are diagnosed with dementia when three things are present:

They have mild dementia if there is only difficulty doing somewhat complicated daily activities, such as paying bills, shopping, or taking medicines. Difficulties with more basic activities of daily living, such as dressing, bathing, and using the toilet, suggest that dementia is in the moderate or severe stage.

Activities of daily living

Complex activities of daily living

Basic activities of daily living

Dementia can be caused by many different disorders

Dementia is not a disease in itself, it is a condition with many different causes. It is like a headache, which could be due to muscle tension, migraines , a blood clot, or a tumor. Just like a headache, some causes of dementia are relatively benign and easily treatable, whereas other causes are more serious and may have no treatment.

Alzheimer’s disease causes dementia about 70 percent of the time, which is why people often confuse Alzheimer’s disease and dementia. Other common causes of dementia include Parkinson’s disease dementia (also called dementia with Lewy bodies), vascular dementia, and frontotemporal dementia. We’ll discuss the specific causes of dementia in later posts.

In mild cognitive impairment, there is a decline in memory or thinking, but the function is normal

We use the term mild cognitive impairment when three things are present:

Individuals with mild cognitive impairment don’t have dementia, because their function is normal.

Although many people with mild cognitive impairment experience a decline in thinking and memory over time, some remain stable, and others improve. Approximately half of the individuals with mild cognitive impairment show a decline in thinking and memory that leads to dementia, at a rate of about 5 to 15 percent per year. However, that means that the other half remain stable or improve.

Like dementia, mild cognitive impairment is not a disease in itself; it is a condition with many different causes. In individuals over the age of 65, Alzheimer’s disease is the most common cause of mild cognitive impairment. Other common causes include strokes and Parkinson’s disease, as well as depression , anxiety , thyroid disorders, vitamin deficiencies, infections, medication side effects, and medical problems.

Subjective cognitive decline may be a sign of a future memory disorder—but not always

If you have noticed that your memory has declined, you are concerned about it enough to see your doctor, and your doctor tested you and told you that your memory is normal, you have “subjective cognitive decline” (sometimes called, “subjective cognitive impairment”). Individuals have subjective cognitive decline when:

Compared to individuals without concerns about their memory, those with subjective cognitive decline are somewhat more likely to end up with a diagnosable memory disorder over five to 10 years.

Does that sound a bit frightening? Please don’t be alarmed. First, most people with subjective cognitive decline don’t end up having a memory disorder, or they have something reversible, such as a vitamin deficiency or thyroid disorder. You should see your doctor to look for these and other reversible causes.

Second, there are specific things that you can do today to help improve your memory and make it less likely that you will end up with a memory disorder in the future, including improving your diet and engaging in aerobic exercise. Lastly, even if you do end up being diagnosed with a memory disorder, many good treatments are available—and the benefits of these treatments are greatest when started early.

Budson AE, O’Connor MK. Seven Steps to Managing Your Memory: What’s Normal, What’s Not, and What to Do About It , New York: Oxford University Press, 2017.

Budson AE, Solomon PR. Memory Loss, Alzheimer’s Disease, & Dementia: A Practical Guide for Clinicians , 2nd Edition, Philadelphia: Elsevier Inc., 2016.

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Andrew Budson, M.D. , is a professor of neurology at Boston University, as well as a lecturer in neurology at Harvard Medical School.

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This article is part of the Bringwise Psychology Journal — daily insights on human behavior, mental health, and personal growth.