The word chronic is used in medicine to refer to any disease or condition which persists over time or is frequently recurring.
This term is often used in contrast to the word acute, which refers to a disease or condition that comes on rapidly and may have a short, severe course.
The U.S. National Center for Health Statistics considers any condition lasting three months or more to be chronic.
Dysthymia is a type of chronic depression in which a person may have symptoms that are less severe than major depressive disorder but linger for at least two years (or one year in children and adolescents).
Although dysthymia is less severe than major depression, its long-lasting nature can make it difficult for an affected person to function in his or her daily life. It may also put the person at an increased risk for suicide.
About half of those with dysthymia will have an episode of major depression at some point in their lives. When an episode of major depression is layered on top of dysthymia this is referred to as double depression.
Treatment for dysthymia usually includes antidepressant medication and/or psychotherapy.