Most commonly family members initiate the diagnostic process by bringing the affected person to the attention of the family doctor. The progressive loss of memory for current or recent events is highlighted, with examples of missed appointments, bills paid late, and repeating stories on the phone. A decreased initiative and planning ability is often quite striking, with reduced participation in conversation. The diagnosis of AD is done primarily by a structured history with the patient and a knowledgeable informant. In addition to memory decline, the diagnosis of dementia requires a change in one other intellectual domain (such as language, recognizing objects and people, using tools, planning and adjusting to circumstances) that interferes with daily life and represents a decline from a previous level of functioning. The typical progression of AD as described in the previous section and a normal neurologic examination strongly support the diagnosis of probable AD (90 percent probability if a microscopic examination of the brain is made from a biopsy or autopsy, in which case the diagnosis can be definite). Other features can be found through history and physical examination that suggest alternative diagnosis: history of strokes or high blood pressure with asymmetric reflexes (vascular dementia or mixed AD and vascular dementia), visual hallucinations and gait instability early in the course (dementia with Lewy bodies), social disinhibition and loss of speech early in the course (fronto-temporal dementia). A concomitant disorder, such as depression, malnutrition, or hypothyroidism, would change the diagnosis of AD to "possible."
A mental status assessment is required when AD is suspected, and can range from the simple but short and reliable Mini Mental State Examination of Martial, Folstein, et al. to a structured and complete neuropsychological examination performed by a psychometrician. This may be required in highly educated individuals suspected of early stage AD, for whom the diagnosis is of some urgency because of occupational or social responsibility. Most often these tests need to be repeated within six to twelve months in order to conclusively demonstrate a decline in two cognitive domains.
The laboratory assessment of AD is currently done to support the clinical impression based on a careful history and physical examination. A minimum workup includes blood count of red and white cells; markers of thyroid, liver, and renal function; and blood sugar levels. In some countries routine additional tests include markers of nutritional deficiencies (B12, folic acid) and of previous infection with syphilis. Brain imaging using computer tomography or magnetic resonance imaging without infusion is most often performed in order to demonstrate brain atrophy and rule out tumors, blood clots, and strokes large or small. It is unusual for a brain scan to change the clinical diagnosis or management.
A number of putative biological markers of AD are under study as adjuncts to the clinical diagnosis. The best known are the blood apolipoprotein E genotype and spinal fluid levels of beta-amyloid fragments and tau. None of these markers has the specificity and sensitivity required for routine use, but this research is important for the day when individuals at risk of AD who are in presymptomatic stages will seek advice for preventive therapy.
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