Diagnostic Tests

Diagnostic evaluation for people having memory difficulties or other cognitive complaints may differ from person to person. A careful history and thorough neurologic evaluation are the fundamental starting point for all patients with cognitive complaints. Our diagnostic testing adheres to American Academy of Neurology guidelines for the evaluation of individuals who may be suffering from memory disorders.

Laboratory investigations

The evaluation of cognitive complaints includes a routine screening for vitamin B12 deficiency and thyroid dysfunction. Additional laboratory tests, which are frequently ordered, are tailored to an individual’s personal medical history, examination findings, occupational or environmental exposures, and other factors. These tests are used to determine whether a medical condition is having a detrimental effect on thinking and memory.

Neuroimaging

The evaluation of cognitive complaints includes either a brain MRI or CT scan. This imaging can determine whether a medical condition is having a detrimental effect on thinking and memory. A brain scan can reveal a history of stroke or the presence of a brain tumor or structural damage to the brain. This structural neuroimaging is carefully reviewed for patterns of atrophy (shrinking) that may suggest a neurodegenerative process. Neuroimaging may also provide clues to diagnoses such as normal pressure hydrocephalus or demyelinating disease.

Neuropsychological testing

Neuropsychological assessment can be an important ancillary test that measures cognitive function and may detect subtle abnormalities in cognitive function. This type of testing typically involves a paper-and-pencil test and verbal tests. Computer-based assessments may also be used. Testing protocols vary, depending upon clinical circumstances, but generally measure memory, language, visuospatial skills, logical reasoning, attention span and general intellectual functioning. Additional measures may include scales that probe symptoms of depression, anxiety or sleep quality. Neuropsychological assessment may provide a useful baseline when following patients with mild cognitive impairment.

Electroencephalogram

In patients whose clinical presentation suggests seizure or encephalopathy, electroencephalogram (EEG) may be helpful to further investigate these possibilities. EEG is a very sensitive test that measures the electrical currents associated with the brain’s cognitive and attention function. It is performed in our office by trained technicians, and the tracing is then interpreted by physicians at UCNI’s Epilepsy Center, who provide an expert review of the EEG.

Cerebrospinal fluid analysis

When an inflammatory or infectious condition is suspected, an analysis of cerebrospinal fluid (CSF) may be necessary to establish the diagnosis. A lumbar puncture and CSF removal may also be performed if a diagnosis of normal pressure hydrocephalus is suspected on the basis of clinical and neuroimaging findings. Ongoing research is providing insights into abnormalities of CSF protein levels that may be associated with Alzheimer’s disease or frontotemporal dementia. However, these tests are not recommended for widespread clinical use at this time. This is due in part to their providing marginal additional benefit in all but the most complex cases. Although CSF analysis may be useful in specific clinical circumstances where a diagnosis is uncertain, most patients do not require lumbar puncture as part of their routine evaluation.

Functional imaging

Functional imaging studies of the brain, such as FDG-PET, may be helpful in differentiating Alzheimer’s disease from frontotemporal dementia. FDG-PET imaging is a nuclear medicine study that images glucose utilization in different regions of the brain. In neurodegenerative diseases such as Alzheimer’s or frontotemporal dementia, specific regions of the brain may demonstrate decreased glucose utilization. The images produced by FDG-PET are registered (lined up) with a CT scan of the head (a picture of the structure of the brain). Thus, the pattern of decreased glucose utilization may aid in determining whether a person has Alzheimer’s disease or frontotemporal dementia.

This type of diagnostic study is not often required, and is generally performed only when a diagnosis remains unclear following neurologic examination and the other types of testing. Brain FDG-PET does require the injection of a radioactive tracer in order to perform the study. Although this involves a small radiation exposure, the test is generally safe. However, brain FDG-PET is expensive, and insurance companies often deny coverage.

Ligand-bound PET

In the future, nuclear medicine studies that utilize a protein that binds amyloid may be helpful in further stratifying the risk that individuals with mild cognitive impairment may see their symptoms progress to Alzheimer’s disease. These tests may also have a role in the evaluation of Alzheimer’s disease or cerebral amyloidosis. In 2011 the Food and Drug Administration (FDA) reviewed an application for a marker that would bind to amyloid. The review panel acknowledged the potential role such a compound could play in clinical practice, but found that the data supporting the application were not strong enough to recommend approval. Specifically, the agreement between different physicians who interpreted the same brain scan was poor. In other words a “positive” scan might be interpreted as “negative” (or vice versa) by a different rater. Only a small number of people having had this type of study were studied at autopsy, and therefore serious questions remain about the validity of finding a “positive” scan. The FDA requested that a better rater training program be developed and that more data about the predictive value of the test be collected. Thus, although this technique holds promise for applications in a memory disorders center, the FDA has not approved a ligand-bound marker for clinical use at this time.

Sleep Center consultation

Unrecognized or untreated sleep disorders decrease a person’s quality of life and may contribute to symptoms of cognitive impairment. As part of a thorough history, our Memory Disorders Center physicians routinely asked questions pertaining to sleep. Some uncommon conditions, such as REM sleep behavior disorder, may result in sleepiness that contributes to cognitive deficits during the day and may be helpful in establishing a clinical diagnosis. Untreated obstructive sleep apnea, which may contribute to cognitive impairments, is associated with an increased risk of heart attack or stroke.