Dementia is not a specific disease. It’s an overall term that describes a group of symptoms associated with a decline in memory or other thinking skills severe enough to reduce a person’s ability to perform everyday activities. Alzheimer’s disease accounts for 60 to 80 percent of cases. Vascular , which occurs after a stroke, is the second most common type. But there are many other conditions that can cause symptoms, including some that are reversible, such as thyroid problems and vitamin deficiencies.
It is often incorrectly referred to as “senility” or “senile dementia,” which reflects the formerly widespread but incorrect belief that serious mental decline is a normal part of aging.