Alzheimer disease
Meaning of Alzheimer disease: Two abnormal proteins, amyloid and tau, accumulate in the brain for years before any memory problem becomes obvious enough to notice.
Definition of Alzheimer disease
Alzheimer disease is a progressive brain disorder that gradually erodes memory, thinking, and behavior, usually beginning in later adulthood. Nerve cells and the connections between them are lost, starting in the regions that handle memory and spreading outward from there. It is the most common cause of dementia, the broader term for cognitive decline severe enough to disrupt daily life.
What happens inside the brain?
Two abnormal protein deposits define the disease. Plaques made of a fragment called amyloid beta collect in the spaces between nerve cells. Tangles of a protein called tau build up inside the cells themselves. Alongside these deposits, nerve cells and their connections are lost and the affected regions shrink. The process begins in and around the hippocampus, a structure central to laying down new memories, which is why recent events fade while distant ones remain. From there it spreads to regions handling language, judgment, orientation and eventually movement. The deposits accumulate for years before any symptom appears, so the biology of the disease starts well before the clinical picture does.
How is it different from dementia in general?
| Term | What it names |
|---|---|
| Dementia | A syndrome: cognitive decline severe enough to interfere with daily life, from any cause |
| Alzheimer disease | One specific disease process, and the most common cause of that syndrome |
| Vascular dementia | Decline caused by damage to the brain's blood supply, often stepwise rather than smooth |
| Lewy body dementia | Decline with prominent visual hallucinations, fluctuating alertness and movement changes |
More than one process can be present at once, and mixed changes are common in older brains. That is part of why the phrase Alzheimer dementia is used when the syndrome is attributed to this disease in particular rather than to dementia in the abstract.
How is it recognized?
Assessment combines a history from the person and from someone who knows them well, cognitive testing, physical and neurological examination, blood tests and brain imaging. Much of that work exists to find other explanations for a decline, since thyroid disease, vitamin deficiency, depression, medication effects, sleep disorders and structural lesions in the brain can all imitate it. Markers of amyloid and tau in spinal fluid, blood or on specialized scans can now support the diagnosis during life, where once confirmation came only from examining brain tissue after death. Inherited forms that run strongly in families and begin unusually early are rare, and genetic testing plays no routine role in the far more common late-onset form.
Also known as
Used in a sentence
The neurologist reviewed cognitive testing results as part of the evaluation for suspected Alzheimer disease.
Good to know
Alzheimer disease is a specific cause of dementia rather than a synonym for the term, since dementia can also result from vascular disease, other neurodegenerative conditions, or a combination of causes.