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Alzheimer disease is one of the diseases that cause dementia. Memory impairment alone is not sufficient for a diagnosis of Alzheimer's. According to the Diagnostic and Statistical Manual of Mental Disorders, 4th edition (DSM-IV), dementia is defined as memory impairment plus one or more of the following: 

  • aphasia - difficulty with language 
  • apraxia - problems with complex movements 
  • agnosia - difficulty with identifying objects 
  • impaired executive functioning - making everyday decisions

Recent studies indicate that individuals diagnosed with mild cognitive impairment (MCI) may in fact be showing very early symptoms of Alzheimer's (Petersen, 2000). Because Alzheimer's has been viewed as untreatable in the past, some physicians, patients and family members are reluctant to push for a diagnosis, or delay doing so until the patient is significantly impaired. However, an early diagnosis is strongly recommended for several reasons:

  • to rule out treatable causes of dementia
  • initiate appropriate therapies
  • develop disease management and caregiving plans
  • make legal decisions while the patient is competent

It is often said that a diagnosis of Alzheimer's can be made definitively only at autopsy, by examing brain tissue for amyloid plaques and neurofibrillary tangles. While this is true, an experienced clinician (such as one working in a university hospital with a major Alzheimer center) can diagnose a living patient with an accuracy of around 90 percent. However, the accuracy of diagnosis may be significantly less - around 50 percent - in community hospitals (see Pearl, G.S., 1997).