How Alzheimer’s disease is diagnosed
Question: Do I need a brain scan to diagnose Alzheimer’s disease?
Answer: Yes, No, Maybe…..
Alzheimer’s disease and dementia are diagnosed by physicians by taking a careful medical history from the patient and a family member, doing a number of brief memory and cognitive tests, and performing a physical exam. Whether your doctor will also order a brain scan might depend on where you live!
In the U.S., it is recommended that everyone being investigated for dementia have a CT scan (Computed Tomography) or MRI (Magnetic Resonance Imaging). In Canada, we suggest that brain scans are only essential in cases where the history and physical exam suggest that the dementia is caused by something other than Alzheimer’s disease (the most common cause of dementia). Even in Canada, however, if you are seen by a dementia specialist, you will likely have a brain scan ordered, because of the extra information the scans can provide. Besides helping with the diagnosis for rarer forms of dementia, they can also help determine the presence of cerebrovascular disease. Cerebrovascular disease (e.g. small and large strokes) can be a primary cause of dementia, but can also frequently be mixed with other pathology like Alzheimer’s disease.
Whether your doctor orders a CT scan or MRI can also depend on a number of factors. CT scans are brief (about 5 minutes), painless, readily available scans, that do expose you to radiation like all X-ray exams. MRI avoids exposure to radiation and provides a much clearer picture of brain structures and more accurate evidence of stroke. Unfortunately, the availability of MRI is much more limited compared to CT, and the procedure can be uncomfortable for many older adults. The scans usually take over half an hour, during which the patient is laying immobile in a long covered tube, which can be difficult for some people with claustrophobia. The machines also produce a lot of noisy banging and clicking, necessitating the need for wearing ear plugs.
Neither CT nor MRI provide direct evidence of Alzheimer’s disease. However, coming soon to a radiology department near you, is another type of brain imaging technique called a PET scan. These scans, available only for research purposes at the moment, actually allow doctors to “see” the typical pathology of Alzheimer’s disease, which begins to accumulate years before the patient will experience any memory or cognitive problems.
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