Alzheimer’s disease (AD), named after Alois Alzheimer, the German psychiatrist who first described it, is the most common cause of dementia and is an irreversible, progressive neurological disorder. Dementia can vary widely in severity, characterized by a loss of cognitive function and changes in behavior, and it is common for more than one form of dementia to manifest in a single patient. For example, AD will commonly occur alongside vascular dementia.

AD usually develops in people older than 65 years; that is termed “late-onset AD.” However, in rarer cases, the disease also can develop in people younger than 65, which is called “early-onset AD.”

Alzheimer’s disease versus dementia

While many use the terms AD and dementia interchangeably, they are different diseases. Dementia is a general term used to describe a group of common symptoms (such as memory loss), usually as a result of damage to brain cells. This can be due to a variety of causes, leading to multiple types of dementia. AD is just one of these causes, and it is associated with a slightly different set of symptoms, treatments, and prognosis compared to other forms.

What happens in Alzheimer’s disease?

AD is a progressive disorder, which means that the number and severity of symptoms will increase gradually over time. In general, the progression is split into three broad stages: early (mild), middle (moderate) and late (severe).

The symptoms experienced by a patient with AD and how quickly they progress will vary from one person to another. The main symptom is memory loss, which can be accompanied by symptoms such as impulsive behavior, mood and personality changes, hallucinations, and confusion.

How is the brain affected by Alzheimer’s disease?

AD results in the damage and death of brain cells, which can lead to significant brain shrinkage as the disease progresses. The root cause of cell death is unknown; however, there are theories based on the common features shared by AD patients. Two of the main features of AD are the formation of “amyloid plaques” and “tau tangles” in the brain.

Amyloid plaques are clumps of protein fragments called beta-amyloid. It is possible that this interferes with the communication between brain cells and eventually leads to nerve cell death.

Tau is a protein that normally forms structures in the brain to transport essential nutrients and molecules into the brain cells. In AD patients, the tau proteins twist and form abnormal tangles inside the cells leading to the collapse of connecting structures. This disrupts the transport system and also is believed to cause the death of brain cells.

Alzheimer’s disease prognosis

There is no cure for AD and the disease is usually fatal. However, there are treatment options available to help manage symptoms and extend life expectancy. Research is ongoing to identify the cause of AD and to develop treatments that can more successfully control the progression of the symptoms.


Alzheimer’s News Today is strictly a news and information website about the disease. It does not provide medical advice, diagnosis or treatment. This content is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition. Never disregard professional medical advice or delay in seeking it because of something you have read on this website.