Mild cognitive impairment (MCI) and dementia are not specific diseases, but rather, each represents a "stage" along the continuum of cognitive impairment and both are generally caused by some underlying disease or condition. The dementia stage is further divided into mild, moderate and severe stages.

There are many diseases and disorders that can lead to MCI then to dementia, including Alzheimer's disease (AD), stroke, Parkinson's disease, Frontal lobe disease, head trauma, certain vitamin deficiencies, hormone deficiencies, metabolic and organ diseases, and depression. Although different diseases may cause decline at different rates, in the case of AD, it generally takes about 7 years for an individual to progress through the MCI stage and then another 7 years to progress from mild dementia through the severe dementia stage.

Mild Cognitive Impairment

When cognitive function is impaired by a medical condition, the earliest and subtlest stages of impairment are called Mild Cognitive Impairment (MCI). If the cause of MCI is not treated, the condition often progresses until the individual is demented. According to widely accepted definitions, persons with MCI have impairments limited to one category of cognitive function (e.g. memory, judgment, reasoning, executive function) and this impairment does not interfere with performing activities of daily living.

Dementia

The definition of dementia has two elements. The first element requires that one has developed difficulties in two or more areas of complex brain function (cognition) such as the ability to:

• Remember what was recently learned
• Recognize and name objects, such as people or other familiar things
• Speak sentences that are understandable to others
• Make decisions or judgments about things that are personally important
• Plan, organize and execute simple and complex tasks

The second part of the definition requires that these "cognitive difficulties" affect one's ability to perform the usual routines of daily life.