Alzheimer’s disease (AD) is a progressive, fatal brain disease. According to the 2011 Alzheimer’s Disease Facts and Figures report from the Alzheimer’s Association, 5.4 million people in the U.S. have Alzheimer’s disease. With the aging of the population, and without successful treatment, there will be 16 million Americans and 106 million people worldwide with AD by 2050.

Increasing age is the primary risk factor for developing AD, but severe memory loss is not a normal part of aging. AD is the most common form of dementia among older people.

What are the symptoms of Alzheimer’s disease?

Alzheimer’s disease affects the areas of the brain that are essential for thinking, memory and behavior. Symptoms of the disease include:

  • Memory loss
  • Tendency to misplace things
  • Trouble performing familiar tasks
  • Changes in personality and behavior
  • Poor judgment
  • Problems with language
  • Impaired visuospatial skills (trouble understanding spatial relationships of objects)

What causes Alzheimer’s disease?

Alzheimer’s disease is caused by the abnormal build-up of proteins in the brain. The build-up of the proteins — amyloid protein and tau protein — leads to cell death.

What are some risk factors for Alzheimer’s disease?

Risk factors for AD include:

Protective factors include:

  • Mental activity
  • Education
  • Physical activity
  • The Mediterranean diet or another healthy diet that includes antioxidants

How common is Alzheimer’s disease?

One in 10 people older than 65 and nearly half of people older than 85 have Alzheimer’s disease. AD can affect people in their 40s. The percentage of people who have AD rises every decade beyond the age of 60.

While AD is the most common cause of dementia (accounting for 62 percent to 70 percent of cases), there are other causes. These include:

How is Alzheimer’s disease diagnosed?

These tests are used to diagnose AD or to rule out other medical conditions:

  • Mental status testing — measures how great a decline in mental functioning (orientation, memory, language skills) exists
  • Neuropsychological testing — assesses mood, thinking and personality
  • Magnetic resonance (MR) scan of the brain
  • Blood tests — blood counts, vitamin levels, liver and kidney function, mineral balance and thyroid gland function tests
  • Positron emission tomography (PET) metabolic or amyloid scanning in some patients

Brain imaging helps to diagnose and understand Alzheimer’s disease. For instance:

  • Magnetic resonance imaging (MRI) can show brain shrinkage (atrophy).
  • FDG PET scans can show lower brain metabolism. (FDG is the tracer molecule used to show how well your tissues and organs are working.)
  • Amyloid PET scans show higher levels of amyloid protein in the brain.

How does Alzheimer’s disease progress (get worse)?

The progression of Alzheimer’s disease can be broken down into stages:

  • No symptoms with Alzheimer’s present in the brain
  • Mild symptoms, with Alzheimer’s changes in the brain. This is called prodromal AD and is the phase before Alzheimer’s dementia.
  • Alzheimer’s dementia
  • Alzheimer’s dementia (mild), in which daily function is beginning to be impaired
  • Alzheimer’s dementia (moderate), in which thinking and memory skills are getting worse. Changes in behavior are common in this stage.
  • Alzheimer’s dementia (severe) is linked to very serious impairment. People in this stage often have trouble walking and experience incontinence.

How do changes in the brain happen because of Alzheimer’s disease?

Key changes in the brain in AD include:

  • Brain shrinkage. This is called atrophy.
  • The loss of nerve cells
  • The presence of neuritic amyloid plaques (protein deposits that collect between nerve cells, or neurons)
  • The presence of neurofibrillary tangles (twisted fibers in the nerve cells, thought to contribute to cell breakdown)
  • Brain inflammation (swelling)

Which medicines are used to treat Alzheimer’s disease?

The medicines used to treat AD include the cholinesterase inhibitors (donepezil, rivastigmine and galantamine), and the NMDA antagonist memantine.

Cholinesterase inhibitors

These drugs work by slowing the breakdown of acetylcholine, the chemical that helps nerves communicate. The medications do not cure AD or stop the progression of the disease. They do help relieve some memory problems and reduce some behavioral symptoms. The most common side effects of these drugs are nausea, vomiting and diarrhea. Some people may have loss of appetite, insomnia or bad dreams.


Memantine blocks a brain receptor that is thought to add to the cellular harm associated with AD. Side effects include drowsiness, headache and dizziness.

Patients can help develop new and better treatments for AD by participating in clinical trials. Cleveland Clinic Lou Ruvo Center for Brain Health is conducting several trials of promising drugs.

What is the outlook for people with Alzheimer’s disease?

Alzheimer’s disease gets worse over time and is ultimately fatal. The course of the disease varies from person to person.

What research is being done on Alzheimer’s disease?

Researchers continue to study medications to treat AD. Carefully designed and conducted studies are needed to give a clear picture of safety and effectiveness before any approval might be considered.


© Copyright 1995-2017 The Cleveland Clinic Foundation. All rights reserved.

This information is provided by Cleveland Clinic and is not intended to replace the medical advice of your doctor or health care provider. Please consult your health care provider for advice about a specific medical condition. This document was last reviewed on: 4/25/2011…#9164