The Stages of Alzheimer's Disease
Alzheimer's disease is a primary neurodegenerative dementia, as opposed to dementia that results from deficiencies in brain perfusion and nutrition. It develops insidiously; the key changes in the brain progress for a long time - years and even decades - before any change in memory, cognition, and behavior is apparent. Today researchers view Alzheimer's as a continuous process that can be divided into three major stages.
Stage 1: Preclinical Alzheimer’s disease
The affected person does not yet exhibit what psychiatrists call cognitve impairment -- symptoms such as memory deficits and confusion about time or place.
However, changes in some telltale parameters (so-called biomarkers) are already measurable. Many such biomarkers for earliest stages of Alzheimer's disease are currently under investigation, but two classes are undisputed:
a) Beta-amyloid (Abeta) and hyperphosphorylated tau, two pathologically changed proteins in the brain and the cerebrospinal fluid in which it is embedded.
b) Shrinking of the hippocampus (a deep brain region that is responsible for memory formation and spatial orientation.
Stage 2: Mild cognitive impairment (MCI) due to Alzheimer’s disease
Mild changes in memory and thinking abilities are noticeable to the person and to family members, but do not affect one’s ability to carry out everyday activities.
There are many causes of MCI that are not related to incipient Alzheimer's disease. The current guidelines define four levels of certainty for arriving at a diagnosis of MCI due to Alzheimer’s disease.
Stage 3: Dementia due to Alzheimer’s Disease
Memory, intellect, navigation in time and space, and behavioral symptoms that impair a person’s ability to function in daily life occur with increasing intensity.