The path to a diagnosis of Alzheimer’s can be a long and uncertain one. Some people have multiple chronic conditions, making it difficult for doctors to identify whether dementia symptoms are caused by a disease or a medication.

A diagnosis of Alzheimer’s is considered conclusive only after death, when the brain can be examined for microscopic changes. In living people, Alzheimer’s diagnosis is usually said to be either probable or possible depending on how symptoms have progressed and whether any other condition could be causing them.

Alzheimer’s is usually diagnosed by a neurologist, psychiatrist, or psychologist. An experienced doctor can diagnose Alzheimer’s correctly about 90 percent of the time.

How Is Alzheimer’s Diagnosed?

Diagnosing dementia is the first step. Dementia is a collection of symptoms and signs characterized by loss of memory and cognitive (thinking and reasoning) function. Alzheimer’s is the most common cause of dementia, accounting for between 60 and 80 percent of cases. Dementia can be caused by other brain disorders, cardiovascular conditions, lead poisoning, and thyroid problems.

Dementia is diagnosed when at least two of the following mental functions are found to be significantly impaired:

• Memory
• Language or other aspect of communication
• Attention and ability to focus
• Reasoning
• Judgment
• Visual processing such as perception of motion, depth, or color

After dementia is diagnosed, the doctor will evaluate possible causes. Criteria for probable Alzheimer’s includes:

• Symptoms began gradually and have worsened over time.
• Work or other daily activities are impaired.
• Several aspects of cognitive ability have declined, as confirmed by someone who knows the person.
• The changes cannot be explained by any other condition.

Criteria for possible Alzheimer’s includes:

• Symptoms began suddenly, or it is difficult to be certain how they began.
• There is evidence of another condition that can cause the symptoms.

Based on all of the above criteria, the doctor will decide how probable a diagnosis of Alzheimer’s disease is. Since several diagnostic criteria may involve waiting to see whether and how certain symptoms progress, the process of diagnosis can take time.

Test and What They Show

Some tests can provide support for a diagnosis of Alzheimer’s, while others are performed to rule out other conditions.

Medical History

The doctor will take a thorough history, asking about symptoms over time, family medical history, previous head traumas, any medications, and possible exposures to toxins. A clear picture may emerge from the medical history that will help a doctor assess risk factors that may strengthen the suspicion of Alzheimer’s or rule out other conditions.

Neurological and Psychological Exams

The doctor will ask questions to determine mental status, cognitive function, and mood. They will carefully examine the eyes and reflexes for signs of nerve damage. The person will be asked to move their arms and legs in specific ways to test for weakness or lack of coordination. The doctor will test for loss of sensation by touching various parts of the body with a vibrating tuning fork, or sharp or dull items. The neurological exam provides an objective assessment of signs and symptoms that may suggest Alzheimer’s or another condition.

Imaging Scans

The neurologist will likely order brain imaging scans such as magnetic resonance imaging (MRI), functional MRI (fMRI), or positron emission tomography (PET). Neuroimaging scans may support the diagnosis of Alzheimer’s if they show certain patterns of atrophy (shrinking) of brain tissues. Brain scans can also rule out other possible causes of dementia such as hemorrhage (bleeding), hydrocephalus (excess brain fluid), or brain damage caused by past strokes. Newer PET scans under development can detect the beta-amyloid plaques that are characteristic of Alzheimer’s.

Blood Tests

Fewer than 5 percent of Alzheimer’s cases are thought to be directly inherited. If the person is younger than 60, the doctor may order a blood test to check for specific genetic markers that could indicate familial Alzheimer’s. Blood samples can also be tested for Huntington’s disease, thyroid dysfunction, and evidence that might indicate cardiovascular problems.

Ruling Out Other Conditions

The process of ruling out similar conditions is referred to as differential diagnosis. Alzheimer’s has symptoms in common with Parkinson’s disease, dementia with Lewy bodies, frontotemporal dementia, and Huntington’s disease.

The doctor may be able to quickly rule many of these conditions based on medical and family history or simple blood tests. Other disorders may require time and repeated tests before they can be confirmed or ruled out. The presence of other diseases in addition to Alzheimer’s may complicate the differential diagnosis and eventually result in multiple diagnoses.

Condition Guide

• Alzheimer’s Disease – An Overview
• Stages of Alzheimer’s Disease
• Symptoms of Alzheimer’s
• Treatments for Alzheimer’s
• Types of Alzheimer’s
• What Causes Alzheimer’s?

FAQ

Should I tell my loved one they have been diagnosed with Alzheimer’s?
A recent study found that only 45 percent of those with Alzheimer’s disease were told of their diagnosis by their doctor. Doctors and family members who do not communicate the diagnosis to their loved ones are likely trying to protect the person from distress. However, some advocates for people with Alzheimer’s believe that this decision deprives a person of planning for their future while they are still able. The decision is a deeply personal one.