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Pathology => Human Diseases => Alzheimer's Disease
Alzheimer's Disease
INTRODUCTION
Alzheimer's Disease, progressive brain disorder that causes a gradual and irreversible decline in memory, language skills, perception of time and space, and, eventually, the ability to care for oneself. First described by German psychiatrist Alois Alzheimer in 1906, Alzheimer's disease was initially thought to be a rare condition affecting only young people, and was referred to as presenile dementia. Today late-onset Alzheimer's disease is recognized as the most common cause of the loss of mental function in those aged 65 and over. Alzheimer's in people in their 30s, 40s, and 50s, called early-onset Alzheimer's disease, occurs much less frequently, accounting for only 10 percent of the estimated 4 million Alzheimer's cases in the United States.
Although Alzheimer's disease is not a normal part of the aging process, the risk of developing the disease increases as people grow older. About 10 percent of the United States population over the age of 65 is affected by Alzheimer's disease, and up to 45 percent of those over age 85 may have the disease.
Alzheimer's disease takes a devastating toll, not only on the patients, but also on those who love and care for them. Patients experience immense fear and frustration as they struggle with once commonplace tasks and slowly lose their independence. Family, friends, and especially those who provide daily care suffer immeasurable pain and stress as they witness Alzheimer's disease slowly take their loved one from them.
SYMPTOMS
The onset of Alzheimer's disease is usually very gradual. In the early stages, Alzheimer's patients have relatively mild problems learning new information and remembering to perform routine mechanical tasks, such as locking the front door or turning off the oven. In time, they begin to have trouble recollecting recent events and finding the right words to express themselves. As the disease progresses, patients may have difficulty remembering what day or month it is, or finding their way around familiar surroundings. They may develop a tendency to wander off and then be unable to find their way back. Patients often become irritable or withdrawn as they struggle with fear and frustration when once commonplace tasks become unfamiliar and intimidating. Behavioral changes may become more pronounced as patients become paranoid or delusional and unable to engage in normal conversation.
Eventually Alzheimer's patients become completely incapacitated and unable to take care of their most basic life functions, such as eating and using the bathroom. Alzheimer's patients may live many years with the disease, usually dying from other disorders, such as pneumonia. Typically the time from initial diagnosis until death is seven to ten years, but this is quite variable and can range from three to twenty years, depending on the age of onset, other medical conditions present, and the care patients receive.
BRAIN ABNORMALITIES
The brains of patients with Alzheimer's have distinctive formations that are recognized as the hallmark of the disease. Under a microscope, these formations are visible as abnormally shaped proteins called tangles and plaques. Tangles are long, silklike tendrils found inside nerve cells, or neurons. Plaques, clumps of silklike fibers, form outside the neurons in the adjacent brain tissue. Not all brain regions show these characteristic tangle and plaque formations-the areas most prominently affected are those related to memory.
In the 1980s scientists found that a type of protein in plaques, called amyloid protein, may actually be toxic to neurons. More recently scientists learned that a protein called tau may be responsible for the characteristic tangles in the brain of an Alzheimer's patient. In healthy brains, tau provides neurons with structural support, but in Alzheimer's patients, this structural support collapses and becomes twisted and tangled.
Scientists have found that neurons in the brains of Alzheimer's patients shrink and eventually die, first in the memory and language centers and finally throughout the brain. This widespread neuron degeneration leaves gaps in the brain's messaging network that may interfere with communication between cells, causing some of the symptoms of Alzheimer's disease.
Alzheimer's patients have lower levels of neurotransmitters, chemicals that carry complex messages back and forth between the nerve cells. For instance, Alzheimer's disease seems to decrease the level of the neurotransmitter acetylcholine, which is known to influence memory. A deficiency in other neurotransmitters, including somatostatin and corticotropin-releasing factor, and, particularly in younger patients, serotonin and norepinephrine, also interferes with normal communication between brain cells.
CAUSES
The causes of Alzheimer's disease remain a mystery, but researchers have found that particular groups of people have risk factors that make them more likely to develop the disease than the general population. For example, people with a family history of Alzheimer's are more likely to develop Alzheimer's disease.
Some of the most promising Alzheimer's research is being conducted in the field of genetics to learn the role a family history of the disease has in its development. Scientists have learned that people who are carriers of a specific version of the apolipoprotein E gene (apoE gene) are several times more likely to develop Alzheimer's than carriers of other versions of the apoE gene. The most common version of this gene in the general population is apoE3. Nearly half of all late-onset Alzheimer's patients have the much less common apoE4 version, however, and research has shown that this gene plays a role in Alzheimer's disease.
Researchers have made similar strides in the investigation of early-onset Alzheimer's disease. A genetic mutation in patients with early-onset Alzheimer's has been linked to the production of amyloid, the protein in plaques that may be implicated in the destruction of neurons. This mutation is particularly interesting to geneticists because it occurs on a gene involved in the genetic disorder Down syndrome. People with Down syndrome usually develop plaques and tangles in their brains as they get older, and researchers believe that learning more about the similarities between Down syndrome and Alzheimer's may further our understanding of the genetic elements of the disease.
Early studies suggested that environmental agents may be a possible cause of Alzheimer's disease; for example, one study suggested that high levels of aluminum in the brain may be a risk factor. Several scientists initiated research projects to further investigate this connection, with mixed results-some studies detected high levels of aluminum in Alzheimer's patients, while in other studies, aluminum concentrations were found to be relatively low. Similarly, investigations into other potential environmental causes, such as zinc exposure, viral agents, and foodborne poisons, while initially promising, have generally turned up inconclusive results.
DIAGNOSIS
Alzheimer's disease is only positively diagnosed by examining brain tissue under a microscope to see the hallmark plaques and tangles, and this is only possible after a patient dies. As a result, physicians rely on a series of other techniques to diagnose probable Alzheimer's disease in living patients. Diagnosis begins by ruling out other problems that cause memory loss, such as stroke, depression, alcoholism, and the use of certain prescription drugs. The patient undergoes a thorough examination, including specialized brain scans, to eliminate other disorders. The patient may be given a detailed evaluation called a neuropsychological examination, which is designed to evaluate a patient's ability to perform specific mental tasks. This helps the physician determine whether the patient is showing the characteristic symptoms of Alzheimer's disease-progressively worsening memory problems, language difficulties, and trouble with spatial direction and time. The physician also asks about the patient's family medical history to learn about any past serious illnesses, which may give a hint about the patient's current symptoms.
VITREATMENT There is no known cure for Alzheimer's disease and treatment focuses on lessening symptoms and attempting to slow the course of the disease. Drugs that increase or improve the function of brain acetylcholine, the neurotransmitter that affects memory, have been approved by the Food and Drug Administration (FDA) for the treatment of Alzheimer's disease.
Evidence shows that there is inflammation in the brains of Alzheimer's patients, which may be associated with the production of amyloid, the abnormal protein in plaques. Preliminary studies suggest that anti-inflammatory drugs may prevent this inflammation, slowing or even stopping the progress of Alzheimer's disease. There is also evidence that the female hormone estrogen may prevent or slow the course of the disease. There is still much to be learned, but as scientists better understand the genetic components of Alzheimer's, the roles of the proteins amyloid and tau in the disease, and the mechanisms of nerve cell degeneration, the possibility that a treatment will be developed is more likely.
VIICARING FOR THE ALZHEIMER'S PATIENT The responsibility for caring for Alzheimer's patients generally falls on their spouses and children. Caregivers must constantly be on guard for the possibility of an Alzheimer's patient wandering away or becoming agitated or confused in a manner that jeopardizes the patient or others. Coping with a loved one's decline and inability to recognize familiar faces causes enormous pain.
The increased burden faced by families is intense and the life of the Alzheimer's caregiver is often called a "36-hour day." Not surprisingly, caregivers often develop health and psychological problems of their own as a result of this stress. The Alzheimer's Association, a national organization with local chapters throughout the United States, was formed in 1980 in large measure to provide support for Alzheimer's caregivers. Today, national and local chapters are a valuable source for information, referral, and advice.
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