Based on my research, medical professionals generally do two things before suggesting brain scans (which “identify strokes, tumors, and other problems that can cause dementia” – Diagnosing Dementia. National Institute on Aging, Bethesda. US.)
- Ask about medical/family history (dementia symptoms, other physical/mental illnesses, medications/supplements, family dementia et. cetera)
- Conduct cognitive assessments and blood tests (The National Institute on Aging also referred to tests on sensory response, reflexes, balance et. cetera)
Brain scans are often used for diagnosing dementia once the simpler tests have ruled out other problems. Like memory tests, on their own brain scans can’t diagnose dementia, but are used as part of the wider assessment. Not everyone will need a brain scan, particularly if the tests and assessments show that dementia is a likely diagnosis.
In recent years, one more avenue for detection has been proposed — Amyloid PET (Positron Emission Tomography) brain scan (in other words, nuclear medicine neuroimaging). Amyloid refers to a type of protein which tends to indicate dementia. The scan was mentioned in Battling dementia before it strikes with new tests that gauge chances of getting condition (20 Sep 2018. Straits Times. Singapore).
According to the same article, the error rate in diagnosis through interview and memory tests by dementia specialists is 30%.
With reference to its usage, I found three articles. [Note that all refer to AD that is Alzheimer’s disease, a common type of dementia. Thus, what about other types?]
Assessment is appropriate for patients with persistent, unexplained mild cognitive impairment, those who meet core clinical requirements for Alzheimer’s disease, or those with progressive dementia and early onset.
Amyloid PET Scan for Alzheimer’s Disease Assessment. (accessed 14 Oct 2018). https://radiology.ucsf.edu/patient-care/services/specialty-imaging/alzheimer. Department of Radiology and Biomedical Imaging at the University of California, San Francisco.
On the other hand, the consensus group discouraged use of amyloid imaging for patients whose management would not be likely to benefit, including:
- Patients with typical AD symptoms, age of onset, and course
- Patients without symptoms or whose symptoms are not confirmed by clinical examination
- Patients seeking to know their risk for AD because of various concerns including family history of dementia or presence of a particular version of the ApoE gene, or patients with a strong family history of early-onset AD seeking an alternative to gene testing.
- Individuals being screened for insurance coverage, employment, or other nonmedical purposes
James M. Ellison. (updated 2 Oct 2018). Amyloid PET Scans: Are They a Game-Changer? https://www.brightfocus.org/alzheimers/article/amyloid-pet-scans-are-they-game-changer. BrightFocus Foundation. Clarksburg, US.
According to the AIT, appropriate candidates for amyloid PET imaging include:
- Those who complain of persistent or progressive unexplained memory problems or confusion and who demonstrate impairments using standard tests of cognition and memory.
- Individuals meeting tests for possible Alzheimer’s, but who are unusual in their clinical presentation.
- Individuals with progressive dementia and atypically early age of onset (before age 65).
Inappropriate candidates for amyloid PET imaging include:
- Those who are age 65 or older and meet standard definitions and tests for Alzheimer’s, since a positive PET scan would provide little added value.
- Asymptomatic people or those with a cognitive complaint but no clinical confirmation of impairment.
Amyloid PET imaging is also inappropriate:
- As a means of determining the severity of dementia.
- When requested solely based on a family history of dementia or presence of other risk factors for Alzheimer’s, such as the ApoE-e4 gene.
- As a substitute for genetic testing for mutations that cause Alzheimer’s.
- For non-medical reasons, such as insurance, legal or employment decisions.
[AIT = Amyloid Imaging Taskforce (AIT)] First guidelines published for brain amyloid imaging in Alzheimer’s. (27 Jan 2013). https://www.alz.org/news/2013/first-guidelines-published-for-brain-amyloid-imagi.