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Full list of author information is available at the end of the articleBackground Approximately 20 % of all patients who experience a major depressive episode develop a chronic course [1] and approxi-mately 47 % of patients who are treated in mental health care facility suffer from some form of chronic depression [2]. Four subtypes of chronic depression are usually distinguished: (1) dysthymia, (2) chronic major depression, (3) recurrent major depression with incomplete remission between episodes, and (4) double depression [3]. Dysthymic disorder is defined as a mild condition that is chronic and persistent for at least 2 years. Major depressive episode, chronic type, refers to a more severe condition that meets full criteria for major de-pression continuously for a minimum of 2 years. Patients who have recovered to the point where they no longer meet full criteria for a major depressive episode but continue to experience significant symptoms for a total duration of illness greater than 2 years are referred to as recurrent major de-pression with incomplete remission during episodes. The superimposition of a major depressive episode on antecedent dysthymia is referred to as double depression [3]. Chronic depression is associated with increased func