Biomarker test in the spinal fluid. A biomarker is something that can be measured to indicate the presence of a disease. Two proteins, beta-amyloid and tau, are found in the brains of people with Alzheimer’s. These proteins can be measured in the fluid that surrounds the brain and spinal cord (cerebrospinal fluid).
The fluid is drawn from the space surrounding the spinal cord during a procedure called a lumbar puncture or spinal tap. It’s checked for signs of beta-amyloid proteins, which form plaques, and tau proteins, which form tangles. Both plaques and tangles contribute to the development of Alzheimer’s disease.
These proteins can distinguish Alzheimer’s disease from other causes of dementia and may help identify people with the disease process before they have significant mental decline. The proteins can support a diagnosis of Alzheimer’s but are not yet used routinely for diagnosis.
Brain imaging (neuroimaging). Researchers are studying imaging techniques, such as MRI and positron emission tomography (PET) scans, used with radioactive tracers. Single-photon emission computerized tomography (SPECT) uses molecular imaging and radioactive tracers. These tests may be able to detect very subtle changes in the brain to identify Alzheimer’s disease even before symptoms start.
Radioactive tracers are charged particles that “light up” Alzheimer’s-affected areas in images of the brain — for example, by attaching to the beta-amyloid and tau proteins associated with Alzheimer’s disease. However, having beta-amyloid in the brain doesn’t mean you have Alzheimer’s disease. More study is needed.
Functional imaging, including fluorodeoxyglucose PET scans, provides detailed images of cells in the brain as they function. The pattern of signal change can determine the cause of dementia.