By Eirish Sison
When large numbers of nerve cells in the brain to stop functioning and lose connections with other neurons, thereby disconnecting parts of the brain that normally work together, dementia is the result. It's not a disease in itself, but rather a blanket term for a set of symptoms relating to loss of brain function. These symptoms may include:
Memory loss is a common early symptom, but having it does not necessarily mean one has or will develop dementia. Dementia is only diagnosed when two or more brain functions — like memory, language, perception or cognitive skills like reason and judgement — are severely impaired.
Dementia can be caused by a number of different diseases including Huntington's disease, Parkinson's disease, Multiple Sclerosis, Lyme disease and HIV/AIDS. Reactions to medications, nutritional deficiencies, infection, poisoning, hormone abnormalities and heart and lung problems have also been known to cause dementia, or dementia-like symptoms. However, the most common and well-known cause of dementia in people aged 65 and older is Alzheimer's disease.
Alzheimer's disease results in degenerative dementia, meaning symptoms get worse over time and are generally irreversible. As the disease progresses, patients' ability to perform basic motor functions gets inhibited. They may have difficulty swallowing and lose bladder and bowel control. Eventually, Alzheimer's sufferers may not be able to recognize relatives or speak, and will typically need total care. The usual life expectancy for those with Alzheimer's is 7-10 years after diagnosis.
The main physical marks of Alheimer's Disease in the brain are abnormal clumps of tissue called amyloid plaques and tangled bundles of fibers called neurofibrillary tangles. It is unknown whether these structures are harmful or if they're merely a by-product of the disease process that damages nerve cells. What is known is that more and more of the abnormalities appear as the disease gets worse. A diagnosis of Alzheimer's disease is made when certain dementia symptoms are present, and other causes of dementia are not found. However, the only way to know for certain that a person had Alzheimer's is to examine brain tissue for plaques and tangles after death.
Published April 12, 2011
Eirish Sison is a San Francisco-based health and science writer.