Neuropsychological Testing or Brain Scans: Which to Choose to Diagnose Dementia? – Dr. Maryanne Edmundson

Sometimes clients ask me, “Why can’t I just get a brain scan to see whether I have dementia?” The answer is that neuroimaging techniques, such as CT scans or MRIs, can be helpful but may not show all the information necessary to determine the presence or absence of dementia. For the greatest certainty, a person concerned about dementia should obtain a neuropsychological evaluation.

What is Neuroimaging?

Neuroimaging is essentially taking a specialized picture of the brain or spinal cord. It shows structure, so it is useful to determine if there are visible changes to the brain, like the development of a tumor or a stroke, that can affect brain functioning. Such scans are especially helpful when a person has a sudden change in functioning (such as difficulty speaking or walking) to evaluate whether quick treatment is needed (such as whether a person should be given medications like TPA to reduce the effects of a stroke). Neuroimaging may also be used to rule out structural brain changes if a person is unable to give meaningful responses to Q&A type testing. However, when it comes to some dementia conditions, such as Alzheimer’s disease, neuroimaging may only show structural changes once the condition is sufficiently advanced to cause visible atrophy in certain brain areas, like the inner temporal lobes. Some studies suggest that MRIs are more likely to show false negatives (i.e., to say a person does not have the disease when they actually do) early in the disease progression (Richard et al., 2013).

What Information Does Neuroimaging Not Provide?

To determine whether a person has dementia, you need to know how they are functioning day to day. Most widely available neuroimaging techniques (CT and MRI) do not show how well the brain is working – they will not tell you if the brain tissue you see on the scan that looks healthy is actually doing what it is supposed to do. Although some brain scans can evaluate narrow functional processes (e.g., EEG shows electrical activity on the brain’s surface, FDG-PET shows how the brain is using glucose) and may relate to daily abilities, they do not necessarily tell specifically how this translates into daily functional performance. Even if there is visible atrophy or functional imaging findings to suggest a particular brain area is not functioning correctly, such scans may not always help your doctor distinguish whether you may have one of several similar conditions. For example, people with Parkinson’s disease may have similar functional testing of dopamine use (a chemical used for brain cell communication) and atrophy patterns to some people with dementia with Lewy bodies and more evaluation is required to determine which they have.

What Is a Neuropsychological Evaluation?

The gold standard for determining whether someone has dementia is a neuropsychological evaluation. This is a comprehensive assessment of a person’s specific symptoms, functional abilities, and medical and emotional history gathered through interviewing, paired with active testing of how a person’s brain is functioning through paper and pencil tasks. Here, a clinician can see that a person is having memory difficulties (e.g., by having them attempt to learn and remember new information) and can put that into the context of their life, including determining whether there has been a change from a person’s previous functioning (even if it is not yet frankly impaired), whether reversible causes of cognitive changes are present (such as medication effects or depression, which cannot be determined by imaging alone), what brain areas are struggling (because certain cognitive tests utilize different brain areas), whether there is a pattern of functional difficulty that fits one dementia vs. another, and what resources or other evaluations may be helpful. Because so much information about the whole person is gathered, a neuropsychologist is able to tailor treatment recommendations to each individual person.

If you have questions about getting a neurocognitive evaluation, consult with your primary medical provider for referral to a local neuropsychologist.