Symptoms and causes

Symptoms

Your brain, like the rest of your body, changes as you grow older. Many people notice gradually increasing forgetfulness as they age. It may take longer to think of a word or to recall a person's name.

But consistent or increasing concern about your mental performance may suggest mild cognitive impairment (MCI). Cognitive issues may go beyond what's expected and indicate possible MCI if you experience any or all of the following:

  • You forget things more often.
  • You forget important events such as appointments or social engagements.
  • You lose your train of thought or the thread of conversations, books or movies.
  • You feel increasingly overwhelmed by making decisions, planning steps to accomplish a task or interpreting instructions.
  • You start to have trouble finding your way around familiar environments.
  • You become more impulsive or show increasingly poor judgment.
  • Your family and friends notice any of these changes.

If you have MCI, you may also experience:

  • Depression
  • Irritability and aggression
  • Anxiety
  • Apathy

Causes

There's no single cause of mild cognitive impairment (MCI), just as there's no single outcome for the disorder. Symptoms of MCI may remain stable for years, progress to Alzheimer's disease or another type of dementia, or improve over time.

Current evidence indicates that MCI often, but not always, arises from a lesser degree of the same types of brain changes seen in Alzheimer's disease or other forms of dementia. Some of these changes have been identified in autopsy studies of people with MCI. These changes include:

  • Abnormal clumps of beta-amyloid protein (plaques) and microscopic protein clumps of tau characteristic of Alzheimer's disease (tangles)
  • Lewy bodies, which are microscopic clumps of another protein associated with Parkinson's disease, dementia with Lewy bodies and some cases of Alzheimer's disease
  • Small strokes or reduced blood flow through brain blood vessels

Brain-imaging studies show that the following changes may be associated with MCI:

  • Shrinkage of the hippocampus, a brain region important for memory
  • Enlargement of the brain's fluid-filled spaces (ventricles)
  • Reduced use of glucose, the sugar that's the primary source of energy for cells, in key brain regions

Risk factors

The strongest risk factors for MCI are:

  • Increasing age
  • Having a specific form of a gene known as APOE-e4, also linked to Alzheimer's disease — though having the gene doesn't guarantee that you'll experience cognitive decline

Other medical conditions and lifestyle factors have been linked to an increased risk of cognitive change, including:

  • Diabetes
  • Smoking
  • High blood pressure
  • Elevated cholesterol
  • Depression
  • Lack of physical exercise
  • Infrequent participation in mentally or socially stimulating activities

Complications

People with MCI have a significantly increased risk — but not a certainty — of developing dementia. Overall, about 1 to 2 percent of older adults develop dementia every year. Among older adults with MCI, studies suggest that around 10 to 15 percent develop dementia every year.