The essential feature of persistent depressive disorder (dysthymia) is a depressed mood that occurs for most of the day, for more days than not, for at least 2 years, or at least 1 year for children and adolescents (Criterion A). This disorder represents a consolidation of
DSM-IV-defined chronic major depressive disorder and dysthymic disorder. Major de- pression may precede persistent depressive disorder, and major depressive episodes may occur during persistent depressive disorder. Individuals whose symptoms meet major de- pressive disorder criteria for 2 years should be given a diagnosis of persistent depressive disorder as well as major depressive disorder.
Individuals with persistent depressive disorder describe their mood as sad or "down in the dumps.” During periods of depressed mood, at least two of the six symptoms from
Criterion B are present. Because these symptoms have become a part of the individual’s day-to-day experience, particularly in the case of early onset (e.g., "I’ve always been this way”), they may not be reported unless the individual is directly prompted. During the 2-year period (1 year for children or adolescents), any symptom-free intervals last no longer than 2 months (Criterion C).
Persistent depressive disorder is effectively an amalgam of DSM-IV dysthymic disorder and chronic major depressive episode. The 12—month prevalence in the United States is approxi- mately 0.5% for persistent depressive disorder and 1.5% for chronic major depressive disorder.
Persistent depressive disorder often has an early and insidious onset (i.e., in childhood, adolescence, or early adult life) and, by definition, a chronic course. Among individuals with both persistent depressive disorder and borderline personality disorder, the covari- ance of the corresponding features over time suggests the operation of a common mecha- nism. Early onset (i.e., before age 21 years) is associated with a higher likelihood of comorbid personality disorders and substance use disorders.
When symptoms rise to the level of a major depressive episode, they are likely to sub- sequently revert to a lower level. However, depressive symptoms are much less likely to resolve in a given period of time in the context of persistent depressive disorder than they are in a major depressive episode.
Temperamental. Factors predictive of poorer long—term outcome include higher levels of neuroticism (negative affectivity), greater symptom severity, poorer global functioning, and presence of anxiety disorders or conduct disorder.
Environmental. Childhood risk factors include parental loss or separation.
Genetic and physiological. There are no clear differences in illness development, course, order. Earlier findings pertaining to either disorder are therefore likely to apply to per- sistent depressive disorder. It is thus likely that individuals with persistent depressive disorder will have a higher proportion of first-degree relatives with persistent depressive disorder than do individuals with major depressive disorder, and more depressive disor- ders in general.
A number of brain regions (e.g., prefrontal cortex, anterior cingulate, amygdala, hip- pocampus) have been implicated in persistent depressive disorder. Possible polysomno— graphic abnormalities exist as well.
The degree to which persistent depressive disorder impacts social and occupational func- tioning is likely to vary widely, but effects can be as great as or greater than those of major depressive disorder.