alzheimers disease

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alzheimers disease

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Alzheimer's Disease or AD

Alzheimer's Disease Diagnosois and Prevention

Alzheimer's disease (also known as AD) is a neurodegenerative disease characterized by progressive cognitive deterioration together with declining activities of daily living and neuropsychiatric symptoms or behavioral changes. It is the most common cause of dementia. The most striking early symptom is short term memory loss (amnesia), which usually manifests as minor forgetfulness that becomes steadily more pronounced with illness progression, with relative preservation of older memories.


As the Alzheimer's disorder progresses, cognitive (intellectual) impairment extends to the domains of language (aphasia), skilled movements (apraxia), recognition (agnosia), and those functions (such as decision-making and planning) closely related to the frontal and temporal lobes of the brain as they become disconnected from the limbic system, reflecting extension of the underlying pathological process. This consists principally of neuronal loss or atrophy, together with an inflammatory response to the deposition of amyloid plaques and neurofibrillary tangles.

Genetic factors are known to be important, and autosomal dominant mutations in three different genes (presenilin 1, presenilin 2, and amyloid precursor protein) have been identified that account for a small number of cases of familial, early-onset AD. For late onset AD (LOAD), only one susceptibility gene has so far been identified: the epsilon 4 allele of the apolipoprotein E gene. Age of onset itself has a heritability of around 50%.

Diagnosis
The diagnosis of Alzheimer's disease is made primarily on the basis of history, clinical observation and tests of memory and intellectual functioning over a series of weeks or months, with various physical tests (blood tests and neuroimaging) being performed to rule out alternative diagnoses. Functional neuroimaging studies such as PET or SPECT scans can provide additional supportive evidence for the diagnosis.

No medical tests other than brain biopsy are available to diagnose Alzheimer's disease conclusively pre-mortem, although meta analysis suggests that SPECT neuroimaging is presently nearly comparable in sensitivity to the clinical exam, and probably better than exam at differentiating types of dementia (Alzheimer's disease vs. vascular dementia) PMID 15545324.


Thus, Alzheimer's disease is primarily a clinical diagnosis based on the presence of characteristic neurological features and the absence of alternative diagnoses, with neuroimaging providing a supporting role where dementia is clearly present, but the type of dementia is questioned. While expert clinicians who specialize in memory disorders can now diagnose AD with an accuracy of 85-90%, a definitive diagnosis of Alzheimer's disease must await microscopic examination of brain tissue, generally at autopsy.

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