HOW TO PROCEED WHEN YOU SUSPECT AD
Step 1: Screening instrument. The first step in the diagnostic evaluation of a patient with suspected AD is to determine if, in fact, cognitive impairment is present. This can be assessed with in-office screening instruments, such as the Mini-Cog (http://bit.ly/1FwQAkG) or Mini-Mental State Examination (MMSE; http://bit.ly/18Djin5), among others.8
Step 2: Clinical evaluation. If observation and test results suggest cognitive impairment, the next step is to determine whether clinical findings are consistent with the diagnostic criteria for AD (see Table 1)9 developed by workgroups from the National Institute on Aging (NIA) and the AA in 2011. A work-up is necessary to identify conditions that can mimic dementia (eg, depression) and behaviors that suggest another type of dementia, such as frontotemporal or Lewy body dementia.10 Lab testing should be included to rule out potentially reversible causes of cognitive dysfunction (eg, hypothyroidism, vitamin D deficiency).
Step 3: Neuropsychologic evaluation. The NIA/AA recommends neuropsychologic testing when the brief cognitive tests, history, and clinical work-up are not sufficient for a definitive diagnosis of dementia.9 This generally involves a referral to a neuropsychologist, who conducts a battery of standardized tests to evaluate attention, memory, language, visual-spatial abilities, and executive functions, among others. Neuropsychologic testing can confirm the presence of cognitive impairment and aid in the differential diagnosis by comparing the patient’s performance in these domains with characteristic features of different dementia syndromes.
Step 4: Brain imaging with either CT or MRI can be included in the work-up for patients with suspected AD to rule out abnormalities (eg, metastatic cancer, hydrocephalus, or occult chronic subdural hematoma) that could be causing cognitive impairment.9,10 Clinical features that generally warrant brain imaging include onset of cognitive impairment before age 60; unexplained focal neurologic signs or symptoms; abrupt onset or rapid decline; and/or predisposing conditions (eg, cancer or anticoagulant treatment).10
The role of biomarkers and advanced brain imaging
Biomarkers that might provide confirmation of AD in patients who exhibit early symptoms of dementia have been studied extensively.11 The NIA/AA identified two categories of AD biomarkers
• Tests for β-amyloid deposition in the brain, including spinal fluid assays for β-amyloid (Aβ42) and positron emission tomography (PET) scans after IV injection of florbetapir or flutemetamol, which bind to amyloid in the brain; and
• Tests for neuronal degeneration, which would include spinal fluid assays for tau protein and PET scans after injection of fluorodeoxyglucose (FDG), which shows decreased uptake in patients with AD.9
Research reveals the promise of these biomarkers as diagnostic tools, particularly in patients with an atypical presentation of dementia or mild cognitive impairment (MCI) that may be associated with early AD.12 (More on MCI in a moment.) However, the NIA/AA concluded that additional research is needed to validate these tests for routine diagnostic purposes. Medicare covers PET scans with FDG only for the differential diagnosis of AD versus frontotemporal dementia.13
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