Alzheimer’s disease (AD), a neurodegenerative disorder, is the most common cause of dementia and characterized clinically by progressive intellectual deterioration together with declining activities of daily living and neuropsychiatric symptoms or behavioral changes. The most striking early symptom is memory loss (amnesia), usually manifest as minor forgetfulness that becomes steadily more dense with illness progression, with relative preservation of older memories. As the disorder progresses, cognitive (intellectual) impairment extends to the domains of language (aphasia), coordinated movement (apraxia), recognition (agnosia) and those functions (such as decision-making and planning) closely related to the frontal lobe of the brain, reflecting extension of the underlying pathological process. This consists principally of neuronal (cell) loss (or atrophy), together with deposition of amyloid plaques and neurofibrillary tangles. Genetic factors are known to be important, and polymorphisms (variations) in three different autosomal dominant genes – Presenilin 1, Presenilin 2, and A-Beta – 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 identitified – the epsilon 4 allele of the APOE gene. Age of onset itself has a heritability of around 50%.
The diagnosis is made primarily by clinical observation and tests of memory and intellectual functioning over a series of weeks or months, with various physical tests (blood tests and brain imaging) being performed to rule out alternative diagnoses. No medical tests are available to conclusively diagnose Alzheimer’s disease pre-mortem, however.
Interviews with family members and/or caregivers can be extremely important in the early phases as well, as the sufferer him/herself may tend to minimize his symptomatology or may be being observed on a day when his/her symptoms are in temporary dormancy.
Initial suspicion of dementia may be strengthened by performing the mini mental state examination, after excluding clinical depression. Psychological testing generally focuses on memory, attention, abstract thinking, the ability to name objects, and other cognitive functions. Results of psychological tests do not easily distinguish between Alzheimer’s disease and other types of dementia but can be helpful in establishing the presence of and severity of dementia. They can also be useful in distinguishing true dementia from temporary (and more treatable) cognitive impairment due to depression or psychosis, which has sometimes been termed “pseudodementia”.
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 the autopsy.
There is no cure, although there are drugs which temporarily reduce neurotransmitter degradation and alleviate some of the symptoms of the disease.