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Core clinical criteria proposed by the National Institute on Aging (NIA) and the Alzheimer’s Association (AA) are intended to facilitate research and the diagnosis of mild cognitive impairment (MCI) by health care providers who do not have access to advanced medical imaging or testing.

In summary, presence of the following are highly suspicious of AD:

 2 or more areas of cognitive defects

 Progressively worsening memory and other cognitive functions

 No disturbance of consciousness

 Onset after age 60

 Absence of other systemic or neurological disorders associated with progressive cognitive defects

Lab studies are performed only to rule out other possible causes for dementia (e.g., cerebrovascular disease, cobalamin deficiency, syphilis, thyroid disease). There is a possible link between vitamin D deficiency and cognitive impairment. However, vitamin D deficiency has not been identified as a reversible cause of dementia.

The American Academy of Neurology (AAN) recommendations suggest that structural neuroimaging with either a noncontrast computed tomography (CT) scan or magnetic resonance image (MRI) is appropriate in the initial evaluation of patients with dementia. In patients with AD, brain MRIs or CT scans can show diffuse cortical and/or cerebral atrophy, but these findings are not diagnostic. Atrophy of the hippocampi (structures important in mediating memory processes) on coronal MRI is considered a valid biomarker of AD neuropathology but some studies suggest that resting-state functional MRI can help better classify AD, mild cognitive impairment, and healthy brains. Another study suggests that MRI can effectively replace invasive studies on CSF biomarkers. Electroencephalography (EEG) is valuable when prion-related diseases are suspected on differential diagnoses. For example, a common finding in Creutzfeldt-Jakob disease is periodic high-amplitude sharp waves. EEG is also useful to distinguish pseudodementia, wherein a normal EEG is found in a patient who appears profoundly demented.

Cerebrospinal fluid (CSF) biomarkers are determined after performing a lumbar puncture. CSF levels of tau and phosphorylated tau are often found to be elevated, whereas amyloid levels are usually found to be low. A reasonable explanation for these low levels is the evidence of amyloid deposition in the brain rather than CSF. The CSF biomarkers provide a statistical sensitivity of 80% and a specificity of approximately 90%. However, routine CSF testing is not a recommendation outside of research settings. Genotyping for ApoE alleles is another research tool to screen populations at risk, but until recently has been considered of little relevance in diagnosis and management of AD.

Before undergoing testing, patients should receive appropriate counseling on the predictive value of genetic testing for AD. Afterward, patients should receive counseling on the implications of the results. Recommendations on pre- and post-test counseling are detailed in the guidelines from the American College of Medical Genetics and the National Society of Genetic Counselors.