Alzheimer’s disease is a progressive brain disorder characterized by changes in the brain that lead to the formation of protein deposits. It is the most common cause of dementia, a condition marked by a gradual decline in memory, thinking, behavior, and social skills. As Alzheimer’s disease progresses, brain cells shrink and eventually die, leading to severe cognitive and functional impairment.

Approximately 6.5 million people aged 65 and older in the United States have Alzheimer’s disease, and worldwide, about 60% to 70% of the estimated 55 million people with dementia have Alzheimer’s.


The key symptom of Alzheimer’s disease is memory loss, which worsens over time. Early signs include difficulty remembering recent events or conversations. As the disease progresses, other symptoms develop, including:

Repeating statements and questions.
Forgetting conversations, appointments, or events.
Misplacing items in unusual places.
Getting lost in familiar locations.
Forgetting the names of family members and everyday objects.
Difficulty finding the right words or expressing thoughts in conversations.

Other cognitive and behavioral changes include difficulty concentrating and thinking, impaired judgment, trouble planning and performing familiar tasks, changes in personality, mood swings, social withdrawal, and delusions.

Despite the decline in memory and skills, some abilities may be preserved longer, such as reading, listening to music, and engaging in crafts.


The exact causes of Alzheimer’s disease are not fully understood, but it involves the failure of brain proteins, leading to damage and death of brain cells. The disease is likely caused by a combination of genetic, lifestyle, and environmental factors that affect the brain over time. In rare cases, specific genetic changes almost guarantee the development of Alzheimer’s.

Researchers are focused on studying the role of two proteins, beta-amyloid (forming amyloid plaques) and tau (forming neurofibrillary tangles), in Alzheimer’s disease.

Risk Factors

The primary risk factor for Alzheimer’s disease is increasing age, with the chances of developing the disease increasing as people grow older. Family history and genetics also play a role, with certain genes like APOE e4 increasing the risk. Down syndrome, being female, mild cognitive impairment, head trauma, air pollution exposure, excessive alcohol consumption, poor sleep patterns, and heart health-related factors like lack of exercise, obesity, smoking, high blood pressure, high cholesterol, and poorly controlled type 2 diabetes are other risk factors associated with Alzheimer’s.

Engaging in lifelong learning, social activities, and maintaining a heart-healthy lifestyle may help reduce the risk of Alzheimer’s disease.


Alzheimer’s symptoms can make it challenging to manage other health conditions and may lead to complications such as difficulty communicating pain, explaining symptoms of other illnesses, or following a treatment plan. As the disease progresses, physical functions may be affected, leading to difficulties with swallowing, balance, bowel, and bladder control, which can result in infections, falls, fractures, poor nutrition, and dehydration.


Alzheimer’s disease is not preventable, but some lifestyle risk factors can be modified. Following a heart-healthy lifestyle, exercising regularly, eating a healthy diet, managing high blood pressure, diabetes, and high cholesterol, and quitting smoking may reduce the risk of dementia. Engaging in mentally and socially stimulating activities is also associated with a lower risk of Alzheimer’s disease. While prevention strategies may not completely eliminate the risk, they can contribute to overall brain health.

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An important part of diagnosing Alzheimer’s disease includes being able to explain your symptoms. Input from a close family member or friend about your symptoms and their impact on your daily life helps. Tests of memory and thinking skills also help diagnose Alzheimer’s disease.

Blood and imaging tests can rule out other potential causes of the symptoms. Or they may help your health care provider better identify the disease causing dementia symptoms.

In the past, Alzheimer’s disease was diagnosed for certain only after death when looking at the brain with a microscope revealed plaques and tangles. Health care providers and researchers are now able to diagnose Alzheimer’s disease during life with more certainty. Biomarkers can detect the presence of plaques and tangles. Biomarker tests include specific types of PET scans and tests that measure amyloid and tau proteins in the fluid part of blood and cerebral spinal fluid.


Diagnosing Alzheimer’s disease would likely include the following tests:

  • Physical and neurological exam

    A health care provider will perform a physical exam. A neurological exam may include testing:

    • Reflexes.
    • Muscle tone and strength.
    • Ability to get up from a chair and walk across the room.
    • Sense of sight and hearing.
    • Coordination.
    • Balance.
  • Lab tests

    Blood tests may help rule out other potential causes of memory loss and confusion, such as a thyroid disorder or vitamin levels that are too low. Blood tests also can measure levels of beta-amyloid protein and tau protein, but these tests aren’t widely available and coverage may be limited.

  • Mental status and neuropsychological testing

    Your provider may give you a brief mental status test to assess memory and other thinking skills. Longer forms of this type of test may provide more details about mental function that can be compared with people of a similar age and education level. These tests can help establish a diagnosis and serve as a starting point to track symptoms in the future.

  • Brain imaging

    Images of the brain are typically used to pinpoint visible changes related to conditions other than Alzheimer’s disease that may cause similar symptoms, such as strokes, trauma, or tumors. New imaging techniques may help detect specific brain changes caused by Alzheimer’s, but they’re used mainly in major medical centers or in clinical trials.

    Imaging of brain structures include:

    • Magnetic resonance imaging (MRI). MRI uses radio waves and a strong magnetic field to produce detailed images of the brain. While they may show shrinkage of some brain regions associated with Alzheimer’s disease, MRI scans also rule out other conditions. An MRI is generally preferred to a CT scan to evaluate dementia.
    • Computerized tomography (CT). A CT scan, a specialized X-ray technology, produces cross-sectional images of your brain. It’s usually used to rule out tumors, strokes, and head injuries.

    Positron emission tomography (PET) can capture images of the disease process. During a PET scan, a low-level radioactive tracer is injected into the blood to reveal a particular feature in the brain. PET imaging may include:

    • Fluorodeoxyglucose (FDG) PET imaging scans show areas of the brain in which nutrients are poorly metabolized. Finding patterns in the areas of low metabolism can help distinguish between Alzheimer’s disease and other types of dementia.
    • Amyloid PET imaging can measure the burden of amyloid deposits in the brain. This test is mainly used in research but may be used if a person has unusual or very early onset of dementia symptoms.
    • Tau PET imaging, which measures the tangles in the brain, is generally used in the research setting.

    In special circumstances, other tests may be used to measure amyloid and tau in the cerebrospinal fluid. This may be done if symptoms are quickly getting worse or if dementia is affecting someone at a younger age than what’s typical.

Future diagnostic tests

Researchers are working to develop tests that can measure biological signs of disease processes in the brain.

These tests, including blood tests, may improve accuracy when making a diagnosis. They also may allow the disease to be diagnosed before symptoms begin. A blood test to measure beta-amyloid levels is currently available.

Genetic testing isn’t recommended for most people being evaluated for Alzheimer’s disease. But people with a family history of early-onset Alzheimer’s disease may consider it. Meet with a genetic counselor to discuss the risks and benefits before getting a genetic test.

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