What is mild cognitive impairment (MCI)?

Supervised by: Atsushi Iwata, Associate Professor, Department of Neurology, Graduate School of Medicine, University of Tokyo

One in four elderly people is said to have MCI or dementia. Alzheimer-type dementia is thought to account for approximately 50% of all cases of dementia. This prevalence is very high, but MCI prior to the onset of dementia is missed in some cases, because the family and other persons around could not recognize the symptoms. The timing of delayed detection influences the subsequent course. Once Alzheimer-type dementia occurs, there is no treatment available that can completely cure the condition. Alzheimer-type dementia is also preceded by a stage of MCI, referred to as “MCI caused by Alzheimer’s disease (MCI-AD).” It is important to be aware of MCI, including symptoms represented by “MCI-AD” and the differences between MCI-AD and Alzheimer-type dementia.

What is MCI-AD?

What is MCI?

In recent years, “dementia” has been increasingly covered by media, such as television and journals, as the population ages. As a result, the term dementia is now well-recognized. However, many people do not seem to know “MCI” well enough.
MCI is the name given to the condition that prevails immediately prior to the onset of dementia. Patients with MCI have memory impairment, like forgetfulness in dementia, but the symptoms are still mild, and it can be said that MCI is an intermediate state between normal and dementia.
Therefore, MCI-AD can be said to be the stage immediately prior to Alzheimer-type dementia. Previous studies have revealed that the accumulation of amyloid-β in the brain, which is a characteristic finding of Alzheimer’s disease, is observed even at the stage of MCI prior to the onset of Alzheimer-type dementia. Namely, accumulation of amyloid-β in the brain is common to Alzheimer-type dementia and MCI-AD. In the context of evidence available up to the present in the medical world, MCI-AD is thought to eventually progress to Alzheimer-type dementia, if left untreated. Therefore, it is important to also have an understanding about MCI-AD, besides being aware of Alzheimer-type dementia.
Differences in symptoms between Alzheimer-type dementia and MCI-AD are described later. Both diseases cause “cognitive impairment,” and it is important to judge “whether or not the cognitive impairment is severe enough to affect people around the patient in daily life.”
MCI-AD is clinically defined as follows.

Clinical definition of MCI

  • The person or his/her family has memory complaints.
  • There is objective evidence of at least one or more cognitive functions (memory, orientation, etc.).
  • Normal activities of daily living
  • No dementia

Patients with a diagnosis of MCI have various underlying diseases causing cognitive impairment, such as Alzheimer’s disease, and this section covers MCI-AD, which is considered to be the most common cause of MCI.

Increasing number of elderly people with MCI

The number of patients with dementia and that of patients with MCI are increasing year after year.
The Ministry of Health, Labour and Welfare reported that among elderly aged 65 years or older, approximately 4.62 million have dementia and approximately 4 million have MCI (as of 2012). The total number of these elderly people is approximately 8.62 million, indicating that one in four (25%) elderly people have dementia or MCI. Thus, dementia is a familiar disease that could be called a national disease. Although Alzheimer-type dementia is said to account for approximately 50% to 70% of all cases of dementia, there are still no clear data on the number of patients with MCI-AD. However, considering that Alzheimer-type dementia accounts for a large proportion of cases of dementia, it is easy to imagine that among patients with MCI, the prevalence of MCI-AD is also relatively high.

Symptoms of MCI-AD

Major symptoms of MCI-AD

As introduced in the above definition, the cardinal symptom of MCI-AD is “memory impairment,” particularly memory impairment over time. While everyone develops forgetfulness with advancing age, MCI-AD is characterized by forgetfulness over time that is inappropriate for age. For example, the following behaviors are seen in daily life.

  • To forget what the patient heard a short time ago and to ask repeatedly
  • To have only a vague memory of recent sensational big news
  • To have only a vague memory of a special event that might have occurred just a few weeks ago (e.g., who got married, where the wedding was held, etc.)
  • To often forget recent events

Differences between MCI-AD and Alzheimer-type dementia

The major difference between MCI-AD and Alzheimer-type dementia is whether the patients can live an independent daily life or not.

People perform various activities in their daily lives, called activities of daily living (ADL), which are divided into “basic ADL (minimum necessary activities, such as feeding, bathing, toileting and dressing)” and “instrumental ADL (somewhat complex activities, such as shopping, housework and managing money).” In Alzheimer-type dementia, both are impaired, making it difficult not only to do housework and shopping, but also to take care of oneself. On the other hand, in MCI-AD, the ability for the basic ADL is normal, while memory impairment influences instrumental ADL, such as housework and shopping. However, patients with MCI-AD do not require care or assistance from family members or people around and their daily lives are not greatly impaired. Since these patients have “memory impairment” inappropriate for age, their daily lives are affected to some extent.

Another difference is the course after the onset. Current medicine has no cure for Alzheimer-type dementia. Although there are treatments to delay the progression of symptoms, Alzheimer-type dementia steadily progresses, albeit slowly. On the other hand, in MCI-AD, appropriate therapeutic intervention could lead to delay in the onset of dementia. Various studies have been conducted on the methods of treatment/improvement of MCI-AD, such as regular exercise, good diet, brain training, and drug therapy, and improvement has been observed in some cases, although improvement cannot be consistently expected.

Early detection of MCI-AD is important

Once MCI-AD occurs, it is said to progress to Alzheimer-type dementia within a few years. Amyloid-β, which causes Alzheimer’s disease, is thought to begin to accumulate approximately 20 years before the onset of Alzheimer-type dementia, and a significant amount of amyloid-β is thought to have accumulated in the brain by the stage a person begins to exhibit MCI-AD. However, the rate of progression to Alzheimer-type dementia varies even after the diagnosis of MCI-AD. Appropriate measures and treatments could delay the onset of dementia. Earlier adoption of measures/treatments for MCI-AD are considered to be more effective. Therefore, early detection of MCI is most important to prevent the future development of dementia. It is important not only for the elderly themselves, but also for people around, such as the family members, to have good knowledge about MCI and to be sensitive to the manifestations of MCI.

Posted jointly with “Dementia-Net.”