Alzheimer’s disease is a brain disorder that cannot be stopped or reversed. The disease severely affects memory, thinking, learning and organizing skills and eventually affects a person’s ability to carry out simple daily activities. Alzheimer’s disease is not a normal part of the aging process.
Alzheimer’s is a disease whose symptoms worsen over time. In fact, scientists believe the disease process may go on for 10 years or longer before the first symptoms of Alzheimer’s disease appear.
When memory problems do begin to be noticeable, they are often identified as mild cognitive impairment (MCI). At this stage, intellectual function is affected but the ability to function and live independently remain intact as the brain compensates for disease-related changes.
In some people, MCI can hold steady at this stage. However, people with MCI are at high risk for progressing to dementia. Alzheimer’s disease is the most common form of dementia. (Dementia can also be due to a variety of reasons such as Parkinson’s disease, dementia with Lewy bodies, vascular dementia, frontotemporal dementia and more.) With dementia, in contrast to MCI, daily function is affected.
As dementia due to Alzheimer’s disease progresses to late stages, affected individuals cannot carry on a conversation, recognize family and friends, or care for themselves.
Alzheimer’s disease is the most common cause of dementia (accounting for 60 percent to 80 percent of cases). Alzheimer’s disease is the sixth leading cause of death in the United States.
One in 10 people older than 65 and nearly half of people older than 85 have Alzheimer’s disease. Alzheimer’s disease can also affect people in their 40s. The percentage of people who have Alzheimer’s disease rises every decade beyond the age of 60. According to the Alzheimer's Association, with the aging of the population and without successful treatment, there will be 14 million Americans and 106 million people worldwide with Alzheimer’s disease by 2050.
Alzheimer’s disease is caused by the abnormal build-up of proteins in the brain. The build-up of these proteins — called amyloid protein and tau protein — leads to cell death.
The human brain contains over 100 billion nerve cells as well as other cells. The nerve cells work together to fulfill all the communications needed to perform such functions as thinking, learning, remembering, and planning. Scientists believe that amyloid protein builds up in the brain cells, forming larger masses called plaques. Twisted fibers of another protein called tau form into tangles. These plaques and tangles block the communication between nerve cells, which prevents them from carrying out their processes. The slow and ongoing death of the nerve cells, starting in one area of the brain (usually in the area of the brain that controls memory) then spreading to other areas, results in the symptoms seen in patients with Alzheimer’s disease.
Symptoms of Alzheimer’s disease vary from person to person and worsen over time. Symptoms of the disease include:
For more information on the stage of disease, click here.
These tests are used to diagnose Alzheimer’s disease or to rule out other medical conditions that cause symptoms similar to Alzheimer’s disease:
There is no cure for Alzheimer’s disease, but available medications temporarily slow the worsening of dementia symptoms and help with behavioral problems that may appear during the course of the disease.
Four medications representing two drug classes are currently approved by the Food and Drug Administration (FDA) to treat the symptoms of Alzheimer’s disease. These drugs are the cholinesterase inhibitors and a NMDA antagonist.
Cholinesterase inhibitors. The cholinesterase inhibitors are all approved to treat the symptoms of mild to moderate Alzheimer's disease (AD). Cholinesterase inhibitors include:
These drugs work by blocking the action of acetylcholinesterase, the enzyme responsible for destroying acetylcholine. Acetylcholine is one of the chemicals that helps nerve cells communicate. Researchers believe that reduced levels of acetylcholine cause some of the symptoms of Alzheimer's disease. By blocking the enzyme, these medications increase the concentration of acetylcholine in the brain. This increase is believed to help improve some memory problems and reduce some of the behavioral symptoms seen in patients with Alzheimer’s disease.
These medications do not cure Alzheimer’s disease or stop the progression of the disease. The most common side effects of these drugs are nausea, diarrhea, and vomiting. Some people may have loss of appetite, insomnia or bad dreams.
NMDA antagonist. Memantine (Namenda®) is approved by the FDA for treatment of moderate to severe Alzheimer's disease. It blocks the neurotransmitter glutamate from activating NMDA receptors on nerve cells, keeping the cells healthier. This medication works differently than the cholinesterase inhibitors. Memantine can be taken alone or taken together with a cholinesterase inhibitor.
Patients with moderate to severe Alzheimer's who were treated with memantine performed better in studies measuring the common activities of daily living such as eating, walking, toileting, bathing, and dressing compared with patients taking placebo. Patient with lower functioning may benefit the most.
Managing behavior changes. Medications are available to treat some of the common behavioral symptoms of Alzheimer’s disease. For example, antidepressant drugs can be used to treat anxiety, restlessness, aggression and depression. Anti-anxiety drugs can be used to treat agitation. Anticonvulsants are sometimes used to treat aggression. Antipsychotics can be used to treat paranoia, hallucinations, and agitation. Some of the side effects of these drugs include confusion and dizziness, which can increase the risk of falls. Therefore these drugs are typically used either for short periods of time, only when behavioral problems are severe, and only after safer and/or other non-drug therapies have been tried first.
All currently approved medications target Alzheimer’s disease after it develops. Scientists are currently researching ways to stop or slow the progress of Alzheimer’s disease before it starts.
Some of the drugs in late-stage investigation are called monoclonal antibodies. These drugs target the amyloid protein that builds up in brain cells. They work by attaching to the amyloid proteins as they float in the brain and remove them, before they form into the plaques and tangles that interfere with the brain’s ability to properly function.
These drugs are still in clinical trials and are several years away from Food and Drug Administration approval in the United States. Early results have been mixed, with some trials showing no improvement in brain function; others showing a slight improvement (less brain function decline). Despite the mixed results, researchers are excited about this new potential method to modify the disease process.
Risk factors for the development of Alzheimer’s disease include:
Researchers believe the presence of the last five risk factors mentioned above might reduce the clearance of amyloid protein from the brain, which then increases the risk of developing Alzheimer’s disease. In particular, the presence of a number of these risk factors at the same time and while the person is in his or her 50s is associated with a higher risk of Alzheimer’s disease.
There may be some ways to reduce the risk of mental decline. In general, living a healthy lifestyle protects the body from strokes and heart attacks and is believed to also protect the brain from cognitive decline. Scientists can’t absolutely prove the cause and effect of the following factors, but studies have shown a “positive association.”
Alzheimer’s disease gets worse over time and is ultimately fatal. Persons with Alzheimer’s disease live, on average, four to eight years after diagnosis. Some patients can live as long as 20 years after diagnosis. The course of the disease varies from person to person.
© Copyright 1995-2020 The Cleveland Clinic Foundation. All rights reserved.
This information is provided by the Cleveland Clinic and is not intended to replace the medical advice of your doctor or healthcare provider. Please consult your healthcare provider for advice about a specific medical condition. This document was last reviewed on: 03/18/2019