Health Topics A-to-Z
Dementia
What Is It? Dementia is a pattern of mental decline caused by different diseases or conditions. Most commonly, dementia occurs when brain nerve cells (neurons) die, and connections between neurons are interrupted. These disruptions have a variety of causes and usually cannot be reversed. Alzheimer's disease causes over 60% of all dementias. Vascular disease, such as stroke, is the second most common cause. Lewy body disease, which causes neurons in…