Alzheimer's disease (AD), also known simply as Alzheimer's, is a neurodegenerative disease that, in its most common form, is found in people over age 65. Approximately 24 million people worldwide have dementia of which the majority (~60%) is due to Alzheimer's.

Clinical signs of Alzheimer's disease are characterized by progressive cognitive deterioration, together with declining activities of daily living and by neuropsychiatric symptoms or behavioral changes. It is the most common type of dementia. Plaques which contain misfolded peptides called amyloid beta (Aβ) are formed in the brain many years before the clinical signs of Alzheimer's are observed. Together, these plaques and neurofibrillary tangles form the pathological hallmarks of the disease. These features can only be discovered at autopsy and help to confirm the clinical diagnosis. Medications can help reduce the symptoms of the disease, but they cannot change the course of the underlying pathology.

The ultimate cause of Alzheimer's is unknown. Genetic factors are clearly indicated as dominant mutations in three different genes that account for the small number of cases of familial, early-onset AD have been identified. For the more common form of late onset AD, ApoE is the only clearly established susceptibility gene. All four genes can contain mutations or variants that confer increased risk for AD, but account for only 30% of the genetic picture of AD. These four genes have in common the fact that mutations in each lead to the excessive accumulation in the brain of Aβ, the main component of the senile plaques that litter the brains of AD patients.

Clinical features

Since family members are often the first to notice changes that might indicate the onset of Alzheimer's they should learn the early warning signs and serve as informants during initial evaluation of patients clinically. The first readily identified symptoms of Alzheimer's disease are usually short-term memory loss and visual-spatial confusion. In the early stage of the disease, patients have a tendency to become less energetic or spontaneous, though changes in their behavior often go unnoticed even by the patients' immediate family. Other behavioral changes are outbursts of violence in people who have no previous history of such behavior. This stage of the disease has also been termed mild cognitive impairment when the patient does not meet the criteria for a diagnosis of dementia.

These initial symptoms progress from seemingly simple and often fluctuating forgetfulness and difficulty orienting oneself in space such as in a traffic lane while driving, to a more pervasive loss of short-term memory and difficulty navigating through familiar areas such as one's neighborhood. As the disease progresses to the middle stage, patients might still be able to perform tasks independently (such as using the bathroom), but may need assistance with more complicated activities (such as paying bills). As the disease advances there is a loss of well-known skills as well as recognition of objects and persons.

In the advanced stage of the disease, deterioration of musculature and mobility, leading to bedfastness, inability to feed oneself, and incontinence, will be seen if death from some external cause (e.g. heart attack or pneumonia) does not intervene. Language becomes severely disorganized, and then is lost altogether. Patients will not be able to perform even simple tasks independently and will require constant supervision.

Once identified, the average lifespan of patients living with Alzheimer's disease is approximately 7-10 years, although cases are known where reaching the final stage occurs within 4-5 years or at the other extreme they may survive up to 21 years.

Diagnosis

No medical tests are available to diagnose Alzheimer's disease conclusively pre-mortem. A definitive diagnosis of Alzheimer's disease must await microscopic examination of brain tissue which generally occurs at autopsy; therefore Alzheimer's disease (AD) is primarily a clinically diagnosed condition based on the presence of characteristic neurological and neuropsychological features and the absence of alternative diagnoses. Determination of neurological characteristics is made utilizing patient history and clinical observation, while neuropsychological evaluation includes memory testing and assessment of intellectual functioning. Neuropsychological screening tests as the Mini mental state examination are widely used but more comprenhensive batteries are recommended. Supplemental testing, including blood tests, neuroimaging, or psychological tests for depression is utilized to rule out other diagnoses or to get extra information on some features of the disease.

Interviews with family members and/or caregivers are also utilized in the initial assessment of the disease, as a patient with Alzheimer's may tend to minimize his or her symptoms, or may undergo evaluation at a time when his or her symptoms are less apparent, as quotidian fluctuations ("good days and bad days") are a common feature of the disease. Observations noting that a patient's memory function decreases over time plays a critical role in the diagnosis of Alzheimer's.

Prevention

Aging itself cannot be prevented, but the senescence of it can be mitigated. However, the evidence relating certain behaviors, dietary intakes, environmental exposures, and diseases to the likelihood of developing Alzheimer's varies in quality and its acceptance by the medical community. It is important to understand that interventions that reduce the risk of developing the disease in the first place may not alter its progression after symptoms become apparent.[citation needed] Due to their observational design, studies examining disease risk factors are often at risk from confounding variables. Several recent large randomized controlled trials—in particular the Women's Health Initiative—have called into question preventive measures based on cross-sectional studies.

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