Compiled from Subject Matter Experts at Johns Hopkins University School of Medicine
Alzheimer’s disease is the most common type of dementia. Worldwide, it accounts for 60-80% of all reported cases of dementia. Dementia refers to a significant intellectual decline that persists over time and affects several areas of cognition or thinking. The condition is often not diagnosed until months or even years after its onset. Memory loss is a universal feature of dementia, but other functions are impaired, such as abstract thinking and language.
Following Alzheimer’s disease, the most common cause of significant memory loss is Vascular Dementia—a disorder often resulting from a series of tiny strokes that destroy brain cells. Other types of dementia include Dementia with Lewy Bodies, Frontotemporal Dementia and Huntington’s Disease.
2) Alzheimer’s Disease
A person in the United States develops Alzheimer’s disease every 68 seconds. The progressive brain disorder is characterized by a gradual deterioration of mental faculties caused by a loss of nerve cells and the connections between them. Alzheimer’s is often accompanied by changes in behavior and personality. People who are 65 and older survive an average of four to eight years after the initial diagnosis.
The human brain is extremely complex with more than 85 billion nerve cells, and there is no certainty that scientists will fully understand how it works anytime soon—even though the brain is responsible for such significant actions as memory, behavior and consciousness. Science has not yet pinpointed the true cause of Alzheimer’s. Traditional theories are based on two factors: 1) neurofibrillary tangles and 2) amyloid plaques.
- Tangles are composed mostly of a protein called tau. These hairlike threads are what remain after a neuron’s internal support structure collapses. In healthy nerve cells, these threads function like train tracks to carry nutrients from one destination to another. In Alzheimer’s, the protein threads becomes hopelessly twisted and useless.
- Plaques are a mixture of abnormal proteins and cell fragments that form in the tissue between nerve cells. Amyloid plaques are gooey and become toxic in areas of the brain responsible for memory, learning and planning. As nerve cell destruction spreads, more of the brain is impacted, especially in the cerebral cortex, which is responsible for reasoning and language. As Alzheimer’s disease progresses, large areas of nerve cells die, brain sections atrophy and the whole brain shrinks in size.
Delirium and dementia are not the same thing and can coexist in one patient. Dementia comes on gradually and is a permanent condition. Delirium is an abrupt change that comes on suddenly and is short-lived, lasting anywhere from hours to days. When a person becomes delirious, it means he or she is confused or disoriented and has difficulty thinking clearly and focusing. People with delirium may not remember events and often misperceive and misinterpret their surroundings—or may not be aware of them. Delirium affects nearly one-third of patients over the age of 65 admitted to hospitals and is most common with patients in the intensive care unit (ICU).
Karin J. Neufeld, M.D., M.P.H. “Recognizing and Treating Delirium.” Memory Disorders Bulletin, Fall 2014, Johns Hopkins Medicine, 28-40.
Peter V. Rabins, M.D., M.P.H. “introductory article to Memory Disorders Bulletin.” Memory Disorders Bulletin, Winter 2014, Johns Hopkins Medicine, 1-14.
Peter V. Rabins, M.D., M.P.H. “Looking Ahead.” Memory Disorders Bulletin, Spring 2014, Johns Hopkins Medicine, 3-24.
Peter V. Rabins, M.D., M.P.H. “The Biology of Memory.” Memory White Paper, 2014, John Hopkins Medicine, 1-4.
Peter V. Rabins, M.D., M.P.H. “Irreversible Dementias” and “Alzheimer’s Disease.” Memory White Paper, 2014, John Hopkins Medicine, 33-65.