Brain changes linking to Alzheimer’s disease (AD) can occur decades before people develop any symptoms. The term for these brain changes is preclinical AD.

Changes in the brain, such as the buildup of abnormal proteins, can signal AD and may occur long before cognitive symptoms develop.

This article looks at preclinical AD, signs and diagnosis, treatment, and outlook.

It also discusses the other stages of AD.

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Changes in the brain that link to AD can occur long before any symptoms of AD appear. The term for these changes is preclinical AD.

Preclinical AD may or may not develop into AD. In preclinical AD, the disease is latent but has the potential to progress to dementia.

Changes such as the formation of plaques and tangles — a buildup of proteins in the brain — may begin a decade or more before any noticeable symptoms relating to memory or thinking occur.

Preclinical AD occurs before any symptoms are present, so the signs of brain changes are only visible through medical tests.

Signs of preclinical AD include the presence of amyloid plaques and tau tangles in the brain.

With AD, abnormal levels of beta-amyloid protein collect and form plaques between nerve cells in the brain, disrupting how they work.

Tau tangles are an abnormal accumulation of tau protein in the brain’s nerve cells, affecting how the cells communicate with each other.

Biomarkers may also show signs of neurodegeneration, which is the gradual loss of nerve cells in certain brain areas and is a key feature of AD.

Preclinical AD can start several years or may last for decades before any symptoms first appear, if they develop at all.

The early changes to the brain in preclinical AD can be very subtle. As medical professionals do not screen for preclinical AD, they usually only notice these changes in experimental research or when a person has diagnostic tests for another reason.

It is also important to know that many people who eventually develop AD or another type of dementia do not show the signs of preclinical AD.

The tests examine certain areas of the brain that may show changes at this early stage.

To diagnose preclinical AD, doctors may use a sample of cerebrospinal fluid to measure for certain proteins that are biomarkers of AD. They may also use brain scans with imaging tests, such as PET or MRI scans, to assess levels of amyloid and tau proteins.

Doctors can use these test results to identify whether or not biomarkers are positive for preclinical AD.

According to a 2020 article, there are no approved drugs for the treatment of preclinical AD, but trials are currently looking at the development of treatments for nonsymptomatic dementia.

Research into medications for preclinical AD is still ongoing. Other potential interventions for preclinical AD that researchers are investigating include:

Some animal studies suggest gingko biloba extract may benefit early stage AD, but this requires further research.

Experts are still researching preclinical AD. They are not yet able to predict whether or not people with preclinical AD will develop AD, nor any potential risk factors for preclinical AD progressing.

Treatment during the preclinical AD stage may help prevent or slow disease progression, although research is still in the developmental stages.

AD usually progresses through mild, moderate, and severe symptoms of dementia depending on the stage of the disease:

Mild cognitive impairment (MCI)

MCI is a change in cognitive abilities that other people may notice but does not significantly affect how the person can carry out daily tasks.

Symptoms of MCI include:

  • forgetting familiar words
  • misplacing items
  • increased difficulty with planning, organizing, or carrying out tasks at home or work

People may still be able to function independently at this stage and may be able to continue their regular activities, such as driving and working.

In some people, MCI may remain unchanging and may not progress. In other cases, it may be an early stage of AD.

Mild dementia

Symptoms of mild dementia include:

  • forgetting information, such as appointments or recent events and conversations
  • decreased judgment or decision-making ability
  • losing the ability to assess time or the steps required in a task
  • change in visual perception

Moderate dementia

Symptoms of moderate dementia include:

  • forgetting important events or personal details, such as their address
  • changes in personality and mood, such as becoming withdrawn or moody in certain situations
  • confusion over time and place
  • wandering and becoming lost
  • physical changes, such as bowel and bladder control, and changes to sleeping patterns

People may remain with moderate symptoms for many years. They may still be able to carry out everyday tasks but may require more assistance.

Severe dementia

Symptoms of severe dementia include:

  • difficulty communicating
  • difficulty walking, sitting, and swallowing
  • increased risk of infections, such as pneumonia

A person may require around-the-clock care at this stage of AD. Over time, symptoms will continue to worsen, and the person may lose the ability to control movement and respond to their surroundings.

Care services can help make a person more comfortable and at ease during this stage.

Rate of progression through Alzheimer’s disease stages

AD usually progresses gradually through mild, moderate, and severe stages, but the rate of progression will differ with each person.

A person may live 4–8 years after diagnosis on average, but this can be as long as 20 years in some people.

Preclinical AD is the term for brain changes linking to AD that occur before any symptoms are present. Preclinical AD may or may not progress to dementia.

Experts are still researching preclinical AD, but treatment of AD in its preclinical and early stages may help prevent or slow down the progression of the disease.