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, develops 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