Dysthymia often co-severe adolescent depression with other mental disorders. A “double depression” is the occurrence of episodes of major depression in addition to dysthymia. In the DSM-5, dysthymia is replaced by persistent depressive disorder. This new condition includes both chronic major depressive disorder and the previous dysthymic disorder.
The reason for this change is that there was no evidence for meaningful differences between these two conditions. The term is from Ancient Greek δυσθυμία, meaning bad state of mind. Poor concentration or difficulty making decisions are treated as another possible symptom. There are no known biological causes that apply consistently to all cases of dysthymia, which suggests diverse origin of the disorder. However, there are some indications that there is a genetic predisposition to dysthymia: “The rate of depression in the families of people with dysthymia is as high as fifty percent for the early-onset form of the disorder”. In a study using identical and fraternal twins, results indicated that there is a stronger likelihood of identical twins both having depression than fraternal twins. This provides support for the idea that dysthymia is in part caused by heredity.
At least three-quarters of patients with dysthymia also have a chronic physical illness or another psychiatric disorder such as one of the anxiety disorders, cyclothymia, drug addiction, or alcoholism”. Double depression occurs when a person experiences a major depressive episode on top of the already-existing condition of dysthymia. It is difficult to treat, as sufferers accept these major depressive symptoms as a natural part of their personality or as a part of their life that is outside of their control. The fact that people with dysthymia may accept these worsening symptoms as inevitable can delay treatment. It has been suggested that the best way to prevent double depression is by treating the dysthymia.