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Mild cognitive impairment (MCI) is a transition stage between the cognitive changes of normal aging and the more serious problems caused by Alzheimer's disease. While mild cognitive impairment can affect many areas of cognition — such as language, attention, reasoning, judgment, reading and writing — most research has focused on its effects on memory.

The disorder can be divided into two broad subtypes. Amnestic MCI significantly affects memory, while nonamnestic MCI does not. Other functions, such as language and attention span, may be impaired in either subtype.

Amnestic MCI has been linked to Alzheimer's disease, while nonamnestic MCI may progress to other types of syndromes — such as frontotemporal dementia, primary progressive aphasia or dementia with Lewy bodies. But some people with MCI don't go on to develop any type of dementia. Some remain stable, while others even revert to normal.

Preliminary reports from a recent Mayo Clinic study suggest that about 12 percent of those over the age of 70 have mild cognitive impairment. People with MCI are three to four times more likely to develop Alzheimer's than those without such impairment.

The forgetfulness of normal aging is minor. You misplace your car keys or lose your car in the parking garage. Perhaps you can't remember the name of a former co-worker when you meet unexpectedly at the grocery store. This is nothing to worry about.

But red flags should go up if you start forgetting things you typically remember, such as doctor's appointments or your weekly pinochle game. This happens to everyone now and then, but if a pattern develops, it could be a symptom of memory-related (amnestic) MCI.

Commonly used criteria for a diagnosis of amnestic MCI are:

• Deficient memory, preferably corroborated by another person
• Essentially normal judgment, perception and reasoning skills
• Largely normal activities of daily living
• Reduced performance on memory tests, compared with other people of similar age and educational background
• Absence of dementia

For either subtype of mild cognitive impairment, there may be more than one underlying cause. The various causes generally are grouped into one of the following categories:

• Neurodegenerative. A disorder that gradually destroys brain cells (for example, Alzheimer's disease, dementia with Lewy bodies or frontotemporal dementia)
• Vascular. A disorder that affects the blood vessels of the brain and the supply of oxygen and nutrients vital to brain cells, causing cell damage and death (vascular cognitive impairment)
• Psychiatric. Certain psychiatric conditions that affect memory, concentration and mood (for example, depression)
• Trauma. Physical injury to the brain that also may lead to cognitive difficulties — the potential cause, such as a history of severe head trauma, is usually obvious

Mild cognitive impairment shares many of the same risk factors as Alzheimer's, including:

• A specific change in a gene, called apoplipoprotein E (APOE) e4, which has been linked to Alzheimer's disease
• Abnormal blood pressure, either too high or too low
• Low levels of physical, social and mental activity
• Fewer years of education
• History of depression

If you're consistently having trouble remembering dates, appointments and other important occasions, you should see your doctor. You may be referred to a memory specialist — who may be a neurologist or a psychiatrist.

Your memory specialist will probably perform an extensive interview. You and your spouse, partner or someone else who knows you well may be asked to describe any changes in your memory, personality and behavior. You may also be asked about your medical history, including medications you're taking and any history of stroke, depression, alcohol abuse, head trauma or other neurological disorders. Blood tests can rule out physical problems that can affect memory, such as vitamin B-12 deficiency or an underactive thyroid gland.

Neuropsychological testing can help assess your memory, language, attention and problem-solving abilities and compare your results with those of people from a similar age and education level. The results help distinguish normal from abnormal cognitive aging, and may help identify patterns in cognitive functions that provide clues to the underlying condition.

People who have mild cognitive impairment are much more likely to eventually develop dementia, particularly Alzheimer's disease. People with amnestic MCI develop dementia at a rate of about 10 percent to 15 percent a year. Older adults who don't have MCI typically develop dementia at a rate of 1 percent to 2 percent a year.

As MCI progresses to dementia, cognitive problems other than forgetfulness become apparent. Although someone with worsening MCI still appears to function normally, he or she is likely to have increasing difficulty concentrating, completing tasks and making decisions.

But about half the people who have MCI don't go on to develop any type of dementia. Advances in brain imaging have allowed scientists to gather data that may help predict whether a person with MCI will develop Alzheimer's in the future.

For example, the hippocampus — a structure in the brain important in memory — is typically smaller in people who progress from mild cognitive impairment to Alzheimer's than in those with MCI who don't go on to develop dementia.

There's still no Food and Drug Administration-approved treatment for mild cognitive impairment.

However, researchers have discovered that donepezil (Aricept) may delay the onset of Alzheimer's disease in people diagnosed with memory-related (amnestic) MCI. Donepezil (Aricept) is commonly used to treat the symptoms of mild to moderate Alzheimer's disease.

During the first year of the three-year study, the rate of progression from MCI to Alzheimer's was much lower in the people who took donepezil (Aricept). However, that difference disappeared by the end of the study.

Other potential therapies being considered for MCI are similar to others being explored for Alzheimer's, including:

• Antioxidants. Substances such as vitamin E and ginkgo biloba may protect brain cells from the oxidative stress that appears to play a role in Alzheimer's, but there's little evidence that either is effective in preventing MCI from progressing to dementia.
• Anti-inflammatory agents. Medications such as nonsteroidal anti-inflammatory drugs (NSAIDs) may reduce inflammation in the brain.
• Drugs that alter brain chemical levels. Medications more commonly used to reduce the symptoms of Parkinson's disease may help normalize the effects of mild cognitive impairment.

Abnormal blood pressure readings, either too high or too low, have been associated with an increased risk of mild cognitive impairment and dementia. Treatment of high blood pressure has been found to reduce the incidence of dementia in the general population.

Lifestyle changes also may reduce your risk. People who have higher levels of social, mental and physical activity seem to have less risk of MCI and dementia.

It's easy to become irritable as you deal with the frustrating symptoms of mild cognitive impairment. Depression also is common in people with MCI. Treatment for the depression may make it easier to deal with the changes you're experiencing in your life.