What is mild cognitive impairment or early dementia?

They aren't the same: Mci involves impairment in one area of brain functioning more than one would expect for your age and previous level of functioning. The impairment can be in memory, judgement, ability to reason or language. Some people who have mci will later develop dementia so it is thought of as a predementia state. Not everyone with mci will develop dementia.

MCI:memory loss only: In dementia, not only memory, but also judgment, language, and other aspects are impaired. Mild cognitive impairment (mci) is a mild worsening of memory without those other changes. Mci may or may not progress to dementia. With my patients, i look for reversible causes, do baseline memory testing and repeat a year later. Slow eeg or prolonged cognitive evoked potential may signal pre-dementia.

MCI: The most important point is that mci does not always progress to alzheimer's. On exam, a good psychiatrist or psychologist can pick up subtle changes in cognition. But does not rise to the level of dementia.