The term "dementia" is often confusing to people outside the medical and psychological professions.  "Dementia" is a syndrome in which a person has impaired memory, plus at least one of the following: problems in executive functions (thinking abstractly, planning, monitoring behavior, appropriately starting or stopping behavior, switching focus, considering consequences); inability to recognize people or objects; inability to use language appropriately; or, inability to perform over learned tasks, such as brushing one's teeth.  Dementia is not a disease itself, but rather a group of symptoms which may accompany certain diseases or physical conditions.

The most common cause of dementia is Alzheimer's disease.  This progressive and insidious disease often starts with short-term memory impairment, and may also include impairment in the ability to recall faces, shapes and distances, and/or the sequence of events.  This disease is not curable, but early treatment may slow the progression of cognitive losses.

The second most common cause of dementia is vascular disease.  This is a condition in which blood flow in the brain is impaired because the blood vessels become "clogged" or damaged (example - a stroke).  This is not the same as Alzheimer's disease; however, here too, the afflicted person becomes progressively worse, and ultimately become incapable of caring for himself.  

Alzheimer's disease and vascular disease account for more than 85% of all dementias.  The remaining dementias may be caused by treatable conditions, such as depression, certain nutritional deficiencies, and some endocrine disorders.  In these cases, the cognitive problems may resolve when the underlying medical issue is addressed.