And two other, very important, symptoms:
- low energy or fatigue
- lack of interest and enjoyment
Sound familiar? "The essential feature is a very long-standing depression of mood which is never, or only very rarely, severe enough to fulfil the criteria for recurrent depressive disorder, mild or moderate severity." (ICD-10). The DSM-IV requires only one year for diagnosis in children. Patients may describe themselves as feeling fine for days or weeks at a stretch between depressive episodes of up to many months duration. As with mild depression, the demands of life can usually be met, albeit with difficulty and at a reduced competency and capacity. This disorder has been estimated to afflict up to 5% of the US population (2-3:1, adult female:male).
Little is known about the origins of dysthymia. In children, it tends to afflict those who have low self-esteem, poor social skills and are pessimistic. Incidence in (all stages of) adulthood tends to be triggered by a major life transition or source of stress; onset may be preceded by a discrete mild depressive episode.
Duration may be indefinite, the disorder may be punctuated by bouts of mild to moderate depression, and regression to recurrent depressive disorder may occur. Ain't life the bastard son of an inbred whore?
As for mild to moderate depression, treatment with antidepressants and/or psychotherapy such as interpersonal therapy (IPT) is decidely effective. Unfortunately, the percentage of dysthymics seeking help is even less than with most depressives; because of the low level of the disorder, many come to view their malaise as normal.
One last thing: as with all depressive disorders, 'mild' and 'moderate' have very different meanings when referring to mental water torture than they do when referring to bean dip. Bear that in mind.
www.mentalhealth.com : ICD-10 (European) and DSM-IV (American) diagnostic criteria
depression.about.com : excellent collection of well-maintained resources and links + a guide with a hairstyle to make the angels weep for joy | 
