One question I am frequently asked is "What is the difference between dementia and Alzheimer's disease?" On one level, the answer to this question is relatively easy and straightforward. Compare the definitions of dementia and Alzheimer's.

Dementia:

Dementia is an impairment of thinking and memory that interferes with a person's ability to do things which he or she previously was able to do. 

Alzheimer's:

Alzheimer's disease is the common cause of dementia, and is particularly common in older people.  Because it is the most common cause of dementia, Alzheimer's disease is commonly equated with the general term dementia.  However, there are many other causes of dementia. 

Distinguishing Alzheimer's disease from other causes of dementia is not always as easy and straightforward as defining these terms.  In practice, people and their disorders of behavior are far more complex than simple definitions sometimes commonly imply.

Alzheimer's: Microscopic Brain Abnormalities
 

Alzheimer's disease is a specific form of dementia having very specific microscopic brain abnormalities.  However, in typical medical practice, we do not have the ability to see microscopic brain abnormalities.

History and Examination for Alzheimer's

Therefore, distinguishing Alzheimer's disease from other forms of dementia requires a doctor to establish certain background information (the history) and define a patient's abilities (the examination), and then perhaps obtain results from certain tests. 

The last step is guided by the results from the first two. Alzheimer's disease is typically a slowly progressive disorder that involves memory for recent information (short-term memory) and one or more other abilities, such as speech and language, personality, decision-making and judgment or awareness and ability to interact with the environment. 

A doctor attempting to distinguish Alzheimer's disease from another form of dementia asks questions about these abilities and examines them as well.  Additionally, the doctor also asks questions about and examines abilities that are typically not impaired in a patient with Alzheimer's disease.  These abilities include, among others, memory for information of long ago (long-term memory), vision, ability to feel things and muscle strength.  In doing these things, the doctor is attempting to determine if the pattern of impairments that the patient has are typical or not typical for Alzheimer's disease. 

CT Scan or MRI for Alzheimer's

After the history and examination are completed, the doctor will commonly obtain a scan of the brain, using either a CT scan or MRI scan.  The scans look at brain large-scale (macroscopic rather than microscopic) structure.  (Newer scan types are being developed to begin to examine brain function and microscopic structure.  In the future, these are likely to help better diagnose Alzheimer's disease.)  Also, the doctor, after the history and physical examination are completed, will commonly obtain certain blood tests.  Which blood tests are obtained will depend on the background history and physical examination.