Early Diagnostic Tests for Alzheimer’s DiseaseEarly Diagnostic Tests for Alzheimer’s Disease
1. After neurological and psychiatric evaluation, neuropsychological testing is essential.
2. Reduced ability to discriminate among smells (odors).
3. Hippocampal and parahippocampal atrophy on MRI scan.
4. Temporoparietal blood flow and metabolism deficits on SPECT or PET.
5. Decreased A-Beta protein amyloid and increased tau protein levels in the cerebrospinal fluid.
6. Presence of apolipoprotein E e4 genotype.
I will cover each of these in more detail.
Neuropsychological (Cognitive) Testing
Neuropsychological testing typically reveals that loss of recent memory is the only deficit in the disease’s earliest clinical stages, which progresses over time to widespread memory loss, great difficulty in naming objects, poor fluency in reciting verbal material, and defects in constructional (drawing a cube, for example) and visuospatial abilities (finding the way to the neighborhood store). However, age and education strongly influence test scores, and these patterns of deficits can occur in conditions other than Alzheimer’s disease. (Mary O’Brien, the steady alcohol user, was wrongly diagnosed with Alzheimer’s disease based on neuropsychological testing.) The great strength of
neuropsychological testing is its ability to pick up subtle, very early memory deficits.
Difficulty Identifying Smells
It sounds a bit strange: difficulty in identifying smells occurs early in the course of Alzheimer’s disease. But there is a sound physiologic explanation: neurofibrillary tangles, a neuropathologic hallmark of Alzheimer’s disease, infiltrate the “olfactory” or smell tract of nerve cells that goes from above the nose to a brain region just below the hippocampus. There are reliable standard tests of smell or olfaction that involve scratching a card and identifying the smell using a multiple-choice format. Our research group recently showed that the inability in people with mild memory loss to accurately identify smells strongly predicts who will later be diagnosed with Alzheimer’s disease. Although the findings were strong, a number of factors can distort he results of the smell test: natural smelling ability varies markedly among people, smell discrimination skills diminish gradually with age, and smoking worsens smelling ability. So this test can provide a guideline but is by no means foolproof.
Brain Imaging in Early Diagnosis
In an earlier chapter, I discussed how an MRI scan can detect reduced size of the hippocampus and how SPECT and PET can detect reduced blood flow or metabolism in the parietal and temporal lobes. These features distinguish Alzheimer’s patients from normal elderly people, but may not be as good in predicting who will get Alzheimer’s in a group of people with mild memory loss. There are a few situations where these imaging procedures may be helpful— for example, a fifty year-old man with mild memory loss who shows the typical MRI and SPECT/PET abnormalities is likely to be developing Alzheimer’s disease.
Taken From: The Memory Program How to Prevent Memory Loss
and Enhance Memory Power
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