Chronic illness dating
According to the fourth edition of the Diagnostic and Statistical Manual of Mental Disorders, published in 1994 (DSM-IV), dysthymia is a serious state of chronic depression, which persists for at least two years (one year for children and adolescents).
Dysthymia is less acute and severe than major depressive disorder..
Patients with double depression tend to report significantly higher levels of hopelessness than is normal.
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".
This study found several areas of the brain that function differently.
The amygdala (associated with processing negative emotions such as fear) was more activated in dysthymia patients.
The fact that people with dysthymia may accept these worsening symptoms as inevitable can delay treatment.
When and if such people seek out treatment, the treatment may not be very effective if only the symptoms of the major depression are addressed, but not the dysthymic symptoms.
This may indicate that there is a developmental difference between these two groups.