There are many causes of memory loss. In addition to the mild decline in memory function that occurs naturally with aging, dementia, which is a pathological decline in memory and other cognitive abilities, has several possible causes. Diagnosing Alzheimer’s disease involves first determining that the symptoms are severe enough to be considered dementia, and then ruling out other causes of dementia besides Alzheimer’s disease.

The damage in Alzheimer’s disease occurs in the brain and there is no way to see inside the brain clearly while a person is still alive. Actually, it is impossible to be certain about an Alzheimer’s disease diagnosis unless a sample of brain tissue (a biopsy) or a postmortem examination of the brain reveals the presence the plaques tangles that are the hallmarks of the disease. Because a biopsy requires brain surgery, this procedure is almost never done to diagnose Alzheimer’s unless there is some other very compelling reason to open up the skull and remove brain tissue (such as a brain tumor). Doctors can almost always determine when a person has dementia, but the cause is not always clear. However, with current testing methods, a skilled doctor can correctly diagnose Alzheimer’s disease in about 90% of cases without performing a biopsy.

There are many causes of dementia besides Alzheimer’s disease. For example, small, undetected strokes can cause dementia by temporarily interrupting blood flow to the brain and killing a small number of brain cells in the area. Parkinson’s disease, another type of neurodegenerative disorder, also can cause dementia. Depression, a common condition in the elderly, may cause memory impairment that may be mistaken for dementia. Several common medications can also impair a person’s ability to think clearly and so can mimic dementia. Several tests may be done in order to rule out these and other possible causes of dementia symptoms before a diagnosis of Alzheimer’s disease can be made.

Diagnosing Alzheimer’s disease

If you suspect you may have Alzheimer’s disease or if a loved one is exhibiting some of the early signs of the disease, make an appointment with a doctor. You may want to make this initial appointment with your (or your loved one’s) regular doctor because talking about such issues can be easier with someone you know. Alternatively, you can seek out a doctor that is well-informed about Alzheimer’s disease for an initial appointment; many nonprofit Alzheimer’s disease organizations have lists of doctors in your area who are knowledgeable about Alzheimer’s disease.

After an initial evaluation, the patient may be referred to a specialist who can help diagnose the cause of their symptoms and prescribe appropriate treatment. Specialists in the diagnosis and treatment of Alzheimer’s disease include neurologists, who specialize in diseases of the nervous system; psychiatrists, who specialize in mental disorders; and psychologists, who may have specialized training in the evaluation of memory ability and other mental functions.

Medical history

Doctors will usually ask about a patient’s medical history and about the medical history of their close family members. For Alzheimer’s disease screening, the doctor will be mostly concerned with the patient’s recent symptoms and if they have worsened over time, as well as if any of the patient’s relatives had Alzheimer’s disease or another type of dementia. They may want to know about any problems the patient has had carrying out daily activities or any changes in personality. If possible, doctors like to speak with a person’s close friends or family members to get more information about their recent behavior. The doctor may also ask about the patient’s diet, nutrition, and alcohol use.

Physical exam

The physical exam for Alzheimer’s disease will likely include the usual vital signs taken at any doctor visit (blood pressure, temperature, and pulse) as well as other general measures of heath. The doctor may listen to the patient’s heart and lungs and take samples of blood and urine for further testing. These tests can be used to determine measures of heart health, like cholesterol, and can also diagnose other conditions that might cause memory loss or other symptoms similar to dementia. Some examples of things that can cause dementia-like symptoms include: anemia, malnutrition, certain vitamin deficiencies, excessive alcohol use, side effects of some medications, infections, uncontrolled diabetes, kidney or liver disease, hyperthyroidism or hypothyroidism, strokes, and circulatory problems in the heart, lung, or blood vessels

Neurological exam

The neurological examination is an additional physical examination to assess the function of the brain and nervous system. It cannot diagnose Alzheimer’s disease but the results can help identify symptoms of brain disorders other than Alzheimer’s such as stroke, Parkinson’s disease, and multiple sclerosis. During a neurological exam, the physician may test:

• reflexes of the knees, feet, elbows, and abdomen
• coordination, balance, and gait
• muscle tone and strength, especially in the arms and legs on both sides of the body
• eye movements
• speech
• ability to perceive different sensations

Mental status tests

If the patient’s medical history and symptoms suggest they may have dementia, and other possible causes for dementia-like symptoms have been ruled out, the doctor will likely order one or more mental status evaluations that measure the patient’s cognitive abilities. These tests examine the patient’s memory, problem-solving abilities, attention span, language skills, and numerical abilities. The tests are designed to determine: 1) if the patient is having cognitive difficulties, 2) what specific cognitive problems the patient is having, and 3) is the patient aware of his or her difficulties. Figuring out which mental processes the patient is having difficulty with and whether or not he or she is aware of the problem can help doctors diagnose the patient and determine what stage the patient is at in the course of the disease.

One example of mental status test is the mini-mental state examination (MMSE), which is commonly used to assess mental function. The test involves asking a patient a series of questions designed to test a range of everyday mental skills. Examples of questions include:

• Remember and repeat a few minutes later the names of three common objects (for instance: horse, flower, penny).
• Count backward from 100 by 7s.
• Spell “world” backwards.
• Name two familiar objects present in the office (as the doctor points to them).
• State what year it is, the season, the day of the week, and the date.
• Give the address of the examiner’s office or of the patients own house including state, city, street, and number.
• Repeat a common phrase.
• Copy a picture of two interlocking shapes.
• Follow a three-part instructional task, such as: untie your left shoe, remove it from your foot, and place it on the table.

The maximum possible score on the MMSE is 30 points and a score of 25 or above is normal. A score between 20 and 24 suggests mild dementia, between 13 and 20 suggests moderate dementia, and less than 12 indicates severe dementia. Researchers estimate that a person with Alzheimer’s disease loses between 2 and 4 points each year from their MMSE score.

Another test for diagnosing dementia is called the Mini-Cog test. The test takes only about three minutes and is a very simple, so it is often used in emergency departments to identify people who may have cognitive difficulties. The test consists of three parts:

• The patient is asked to repeat three common objects (the same as in the MMSE).
• The patient is asked to draw the face of a clock showing all twelve numbers in the right places and displaying a specified time.
• After drawing the clock, the patient is then asked to recall the three words from the first part of the test.

If the patient is unable to recall any of the three words then they are categorized as “probably demented,” while if they are able to recall all three words they are categorized as “probably not demented.” If they can recall one or two words the results of the clock drawing test are used to categorize them: if the patient draws a clock that is in any way abnormal they are considered “probably demented,” while if their clock is normal they are considered “probably not demented.” At best, the results of the Mini-Cog are suggestive. Further testing is necessary to conclude that a person has dementia.

In addition to assessing mental status, the doctor will also evaluate the patient’s overall mental health and well-being to determine if they are depressed.

Neuropsychological tests

Sometimes doctors may suggest more extensive psychological testing to examine the patient’s cognitive deficits in more detail. These tests assess different aspects of memory (including short-term, long-term, memory for facts, and memory for life events), problem-solving abilities for several types of problems (logic, math), attention span, counting ability, and language skills. More extensive testing is helpful in trying to detect dementia at an early stage and in discriminating between possible causes of dementia, including Alzheimer’s disease.

Brain imaging

Brain imaging involves using sophisticated medical equipment to take pictures of the brain though the skull. Recent improvements in imaging technologies now allow medical technicians to produce high resolution structural and functional images of the living brain. Structural imaging provides information about the shape, size, and architecture of a person’s brain, while functional imaging reveals how well cells in different brain regions are working by displaying their use of sugar or oxygen.

Structural techniques include magnetic resonance imaging (MRI) and computed tomography (CT). Both of these techniques can detect changes in the size of the brain and its general structure. MRI has better resolution and so it is the preferred method for examining the brain of someone suspected of having Alzheimer’s disease. While the images cannot show whether a person has the plaques of tangles characteristic of Alzheimer’s disease, they can be used to detect tumors, evidence of pervious strokes, fluid buildup, or damage from head trauma, all of which can cause dementia-like symptoms similar to Alzheimer’s disease.

Functional imaging techniques include positron emission tomography (PET) and functional MRI (fMRI). A PET scan can help distinguish between Alzheimer’s disease and frontotemporal dementia, a rare, related disorder that causes reduced function in the frontal (front) and temporal (side) regions of the brain. Both functional imaging techniques are also being studied to see if they can help predict or diagnose dementia and Alzheimer’s disease based on changes in brain activity. Some research in this area suggests that people with Alzheimer’s typically have reduced brain activity in certain regions, while other studies indicate that people with very early Alzheimer’s may have increases in brain activity in certain regions. However, there is not yet enough information to allow functional imaging to be used to diagnose or predict Alzheimer’s.