Laboratory tests can be performed to rule out other conditions that may cause cognitive impairment. Current recommendations from the American Academy of Neurology (AAN) include measurement of the cobalamin (vitamin B12) level and thyroid function testing. AAN guidelines also state that structural neuroimaging (ie, CT scan or MRI of the brain) is appropriate to detect lesions which may result in cognitive impairment. Additional investigations are performed at the discretion of the physician and are tailored to the individual patient.
Initial test results that require further workup include the following:
Abnormalities in complete blood cell count and cobalamin (vitamin B12) levels, to rule out hematologic disease
Abnormalities in liver enzyme levels, to rule out hepatic disease
Abnormalities in thyroid-stimulating hormone levels, to rule out thyroid disease
Abnormalities in the rapid plasma reagin test, to rule out syphilis
Abnormalities in HIV serology and/or polymerase chain reaction assay, to rule out HIV/AIDS
Abnormalities in paraneoplastic antibodies, to rule out autoimmune encephalitis
Abnormalities in cerebrospinal fluid proteins tau, P-tau, and 14-3-3, to rule out Creutzfeldt-Jakob disease
CSF measurement of tau and beta-amyloid is rarely part of the diagnostic workup for Alzheimer's disease, except in the research setting; however, this may change in the future with the development of therapies to slow the rate of progression of Alzheimer's disease.
In clinical research studies, atrophy of the hippocampi (structures important in mediating memory processes) on coronal MRI is considered a valid biomarker of Alzheimer's disease neuropathology. Nonetheless, measurement of hippocampal volume is not used in routine clinical care in the diagnosis of Alzheimer's disease.
Brain scanning with SPECT or PET is not recommended for the routine workup of patients with typical presentations of Alzheimer's disease. These modalities may be useful in atypical cases or when a form of frontotemporal dementia is a more likely diagnosis.
Learn more about the workup of Alzheimer's disease.
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